Download 1 Ministry of Health of Ukraine Higher State Educational Establishment

Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Electrodynamics. It medical use. Bases of medical
equipment.
Bases of an electrodynamics. The medical equipment. The
analysis of work of Wheatstone bridge (electric balance).
Measurement of an electrical resistance.
1
medical, stomatological
Poltava – 2016
1
The topic significance:
The measurement of electrical resistance is the widely widespread procedure in
engineering and scientific researches, including biophysics. The methods of
measurement of resistance, which are used in the given time, are very various, but one
of most widespread and exact is the method of Wheatstone bridge (electric balance).
Electric balances are used for measurement of impedance and capacitance too.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
To form the professional experience by reviewing, training and authorizing it;
To be able to carry out laboratory and experimental work.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing disciplines): To know concepts: electric field, potential, potential
physics, mathematics,
difference,
gradient. Ohm’s
law,
electrolytic
chemistry, biology
dissociation, diffusion potential
(electrochemical
potential)
To describe them.
To describe electrokinetic appearances, membrane’s
pumps work, membrane’s permeability
Subsequent disciplines:
To know role of electric processes in cell, tissues and
Normal physiology
whole organism functioning.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Bridge
Measuring devices for measurement of impedance,
resistance, capacitance and inductance also. Use
balancing of currents in electric circuit.
Impedance
Integral electrical resistance of objects.
Dispersion of
impedance
Graduated changes of impedance on change of alternating
electric field frequency
Polarisation
Charges in substance have an opportunity to move from
one electrode to another under activity of electric field in
restricted volumes, forming inner electric field opposite in
relation to the outer electric field calling polarisation.
Relaxation time
Time of originating of dipole polarization.
Bias current
Current of bound charges under activity of a field have an
opportunity to move, forming a current of conduction,
limited in time.
Theoretical questions to class:
1. Ohm's law.
2. Bridges theory.
3. The Wheatstone bridge.
2
4. Impedance.
5. Electical properties of biological tissues.
6. Polarisation in electrostatic field.
7. Alternationg current in biological tissues.
Practice work executed at class:
Task. Measure of unknown resistance with Wheatstone bridge help.
Recommendations.
– to assemble the bridge according to circuit;
– to balance the bridge (galvanometer G – fig.1 – reads zero);
– to calculate value of every of both unknown resistances Rx1 and Rx2 by
formula:
R  R
Rx  
.
R
If R1=R2 then Rx=R3.
– To measure total resistance of parallel connection of resistances Rx1 and Rx2;
– To calculate total resistance of parallel connection of resistances Rx1 and Rx2
and compare with measured value; to draw a conclusion;
– To measure total resistance of series connection of resistances Rx1 and Rx2;
– To calculate total resistance of series connection of resistances Rx1 and Rx2
and compare with measured value; to draw a conclusion;
To draw the conclusion.
Contens of the topic.
Bridges are among the most accurate types of measuring devices used in the
measurement of impedance. Bridges are used for precision measurements of
resistance, capacitance and inductance also.
Fig.1. The circuit diagram of the Wheatstone bridge for resistance measurement.
Fig.2. The circuit diagram of the Wheatstone bridge for impedance measurement.
3
Resistors R1 and R2 are precision and constant resistors, R3 is variable resistor
(or resistor bank). Resistor bank is set of resistors, that can be arranged for reaching of
any value between lead terminals of bank. The value of Rx is an unknown; it is
resistance that must be determined. The galvanometer (an instrument that measures
small amounts of current) is inserted across terminals C and D to indicate the condition
of balance. When the bridge has been balanced perfectly, no difference in potential
exists across terminals C and D, the galvanometer G reads zero. In this case the
unknown resistance value is equal to R3.
When the battery on, electron stream flows from the negative terminal of the
battery to point A. It corresponds to the current direction from + to –. In point A the
current divides between two parallel circuit. Part of it passes through R1 and R2, other
passes through Rx and R3. The two currents I1 and I2 unite at point B and return to the
positive terminal of the battery.
According to Ohm's law, the current is inversely proportional to the resistance. In
case of breakage bwtween points C and D the value of I2 depends on the sum of
resistance R2 and R3, and the value of I1 depends on the sum of resistances R1 and Rx.
At presence of galvanometer G if Rx ≠ R3, currents I3 and I4 are not equal, current
flows through galvanometers G. If R1 = R2 and Rx = R3, currents I3 and I4 are equal, no
current flows through galvanometers G.
If resistors R1, R2, and R3 are different, when no current through galvanometers
R  R
G, next expression is valid: R x  
.
R
When exemined object has resistive and capacitor properties, used balance
scheme corresponding to scheme represented on fig.2.
The Wheatstone bridge illustrates the concept of a difference measurement,
which can be extremely accurate. Variations on the Wheatstone bridge can be used to
measure capacitance, inductance, impedance and other quantities, such as the amount
of combustible gases in a sample, with an explosimeter. The Kelvin bridge was
specially adapted from the Wheatstone bridge for measuring very low resistances. In
many cases, the significance of measuring the unknown resistance is related to
measuring the impact of some physical phenomenon – such as force, temperature,
pressure, etc. – which thereby allows the use of Wheatstone bridge in measuring those
elements indirectly.
The Wheatstone bridge is the fundamental bridge, but there are other
modifications that can be made to measure various kinds of resistances when the
fundamental Wheatstone bridge is not suitable.
Electrical measurements in biology and medicine.
Electric conductivity of cells and tissues
Passive electrical properties are inherent in biological objects: resistance and
capacity (condensance). Studying of passive electrical properties of biological objects is
of great importance for comprehension of frame and the physicochemical state of
biological substance.
Biological objects have properties as conductors, and dielectrics. Presence of
free (loose) ions in cells and tissues causes conduction of these objects.
In the circuits keeping capacitors or inductances, resistance to alternating current
depends on frequency of current, there introduces concept of an impedance - efficient
resistance to alternating current.
At current passage through a living tissue it experimentally established, that this
circuit has properties both the active resistance, and capacity. It is proved by a
4
calorification and decrease of the complete resistance of a tissue with ascending
frequency.
Properties of inductance practically it is not found out in a living tissue. Thus, the
living tissue represents the composite, but not the complete electric network.
The impedance for RC-circuits can be considered both for serial, and for parallel
connection of their elements. In more complex circuits impedance can be calculated by
consecutive, sequential calculations of impedance for small simple parts of circuit, with
following using of received results to the following calculations.
Resistance and capacitance in series: Z   X c  R  .
Resistance and capacitance in parallel:



.
R
Electric conductivity of cells and tissues. Equivalent circuitry of the living
Z

X c

tissue
The equivalent circuitry of a living tissue is the conditional model approximately
describing a living tissue, as a conductor of alternating current.
If as model of a living tissue to take multicellular medium, than at drawing up of
the equivalent circuit it is necessary to take into account pathes of electric current.
Their two: around of a cell, in extracellular medium and through a cell. The path
around of a cell is submitted only by environmental resistance Renv.
A path through a cell resistance of contents of cell Rc, and also resistance and in
capacity of membrane Rм, Cm.
The circuit allows considering: what electrical elements the tissue as these
elements as properties of a tissue will vary at change of current frequency.
In a circuit basis three positions lay: the extracellular medium and cell contents
are ionic conductors with the active environmental resistance Renv and cells Rc, the
cellular membrane is a dielectric, but not ideal, and with a small ion conductance, and,
hence, and membrane resistance Rм, the extracellular medium and the cell contents
separate by a membrane, are condensers of Cm of fixed capacity (0,1 - 3,0 mkF/sm2).
Electric conductivity of cells and tissues for the direct current
At direct current transmission through living tissues it established, that the current
intensity does not remain to constant in time though the put voltage does not variate.
The current intensity after superposition of potential difference starts to be
decreased continuously and after a while is positioned
on a fixed level.
Thus it decreases in hundreds and even
thousand times in comparison with a reference value.
Change of a current (J) in time (t)at
superposition on a tissue of a stationary value of
potential difference. a - value of a current at absence of
polarization; b - value of a current at presence of
polarization.
5
At transit of a direct current through biological system in it arises electromotive
force of an opposite direction increasing up to some limen (polarizations electromotive
force), which reduces enclosed to object efficient electromotive force, as results in
decrease of a current. Electromotive force of polarizations P(t) is function of time. Then
the Ohm's law for biological object should be written down:
I = (U–P(t))/R.
Originating of electromotive force of polarization is connected to ability of living
cells to accumulate charges at current transit through them, i.e. with the capacitive,
dielectric properties of biological objects caused by phenomenon of polarization.
More the complete information on biological object can be received at measuring
its electric conductivity on an alternating current, therefore now studying of electrical
properties of biological systems is routinely effected on an alternating current.
As biological systems are capable to accumulate electric charges at transit
through them of a current their electrical properties need to be featured with the help of
ohmic resistance. It is necessary to use also concept of electric capacity.
The capacity is quotient of proportionality between a charge and potential and is
defined as the attitude of change of charge Δq of a conductor to change of its potential
Δφ: C = ΔQ/ Δφ.
For a parallel-plate capacitor it is defined under the formula: C = εS/4πd,
where S - the area of plates; d - distance between them.
The measured capacity of biological object is defined by polarization capacity
which arises at the moment of transit of a current. The polarization capacity reflects the
attitude of change of a charge of object to change of its potential at transit alternatingcurrent.
The considerable on quantity a direct membranes capacitance joins to
polarization capacity of biological object. Quantity of polarization capacity depends on
time of activity of a field and can exceed on low frequencies quantity of a direct
capacitance.
On higher frequencies (about 10 kHz) the direct capacitance on some orders is
higher polarization. And as these capacities paired serially, on high frequencies general
quantity of capacity is determined smaller on quantity in polarization capacity.
Electric model of biological object can be submitted as various combinations of
capacities and resistances – as various equivalent circuits. The most prime are
equivalent circuits with serial and a connection in parallel C and R.
As biological objects have both conduction, and capacity they will be
characterized as the active resistance, and reactance. Reactive capacitive reactance Rx
is determined under the formula: R = 1/ ωC,
where ω - circular frequency of a current.
Integral resistance of objects is termed as impedance. For a series connection of
C and R the impedance is determined under the formula:
Z = R – i/ωC.
For parallel - under the formula: 1/Z = 1/R – iωC, where Z - impedance; i imaginary unity, i.e. √(-1).
Frequency-dependent character of a capacitive reactance is one of the causes of
dependence of an impedance of biological objects from current frequency, i.e. a
dispersion of impedance.
Dielectric properties of biological objects and quantity of inductivity are defined by
structural builders and phenomenon of polarization.
Dispersion of impedance
If time, during which the electric field is guided to one side, is more than
relaxation time of any type of polarization, that polarization achieves the maximal value,
and the substance will be characterized to certain constant values by efficient inductivity
6
and conduction values. Until the half-period of alternating-current is more than
relaxation time, efficient inductivity and conduction of object will not variate with change
of frequency.
If at frequency augmentation the half-period alternating-current becomes less
relaxation time, that polarization has not time to achieve maximal value. After that
inductivity starts to be decreased with frequency, and conduction - to grow.
Fig. A dielectric dispersion of a muscle tissue.
α-Dispersion occupies range of low frequencies of a sound diapason,
approximately up to 1 kHz. In the given range decrease of biological systems inductivity
is caused only by decrease of polarization effect of a cells surface as the electric current
with frequency up to 1 kHz runs practically only on intercellular interspaces as cells
resistance for currents of low frequency is great. Both homogeneous, and the particles
surrounded with membranes find out identical properties on the given frequencies. αDispersion has been obtained for glass particles, polystyrene spheres and fatty
particles, suspended in electrolyte and having by a double electrical layer. It
convincingly shows, that the apparent dispersion is caused by properties of all particle
surface.
β-Dispersion occupies wider range of frequencies: 103-107 Hz. In past for an
explanation of a dielectric dispersion and resistance in the given range of frequencies
there frequently reverted to the theory of dipole polarization. According to this theory,
large moleculas of organic substances (proteins, nucleic acids, etc.) have electrical
dipole moments of major quantity. Orientation of dipole molecules under activity of an
electric field causes major values of inductivity in the given range of frequencies. At
augmentation of frequency of a current dipoles have not time to turn after a field that
results in decrease of ε. At high frequency dipole polarization will not be observed
absolutely and inductivity again becomes stable.
γ-Dispersion of tissues inductivity (dielectric permittivity) is observed on
frequencies above 1000 MHz. Decrease of inductivity in the given gamut is caused by
weakening of effect of polarization, which produced by water dipoles.
Quantity of γ-dispersions will depend on free water content in explored tissues. In
range of 400 MHz (between β- and γ-dispersion) ε quantity for tissues (except for futty,
osteal and cerebral) lays in limens 40-60 in dependence on the free water content.
In range of superhigh frequencies (it is more than 1010 Hz) effect of polarization
caused by dipoles of water, will miss. Inductivity will have small values determined by
ionic and electron polarization, having smallest relaxation time.
POLARIZATION
Substances have free and bound charges. Free charges (electrons and ions)
under activity of electric field have an opportunity to move from one electrode to
another, forming a current of conduction. It is necessary to note, that in cells free ions
can move under activity of a field in restricted volumes - from one membrane up to
another. Bound charges under activity of a field have an opportunity to move only in the
some, frequently very restricted limits. At the movement they form bias current (offset
current, currents of shift).
7
Process of travel of bound charges under activity of an electric field and
formation thereof electromotive force, directional against an external field, is termed as
polarization. Time of originating of dipole polarization is termed relaxation time.
Polarization by the nature is divided into some types.
Electron polarization is a result of electron shells shift in relation to position of
nucleus: electron shells by electric field lines, nucleus – in opposite direction. It make
neutral atom dipole.
As a result of such shift the atom or an ion turns in induced electrical dipole with
a direction, counter to an external field.
Time of originating of electron polarization after instantaneous (momentary)
superposition of the field, termed as a relaxation time, is equaled 10-16-10-14 s.
Incipient electrical dipole moment has small quantity.
Ionic polarization - shift of an ion concerning a crystal lattice. Thereof there is
an electrical dipole moment with a direction, counter to an external field. A relaxation
time of ionic polarization 10-14-10-12 s.
Dipole (orientation) polarization. If the substance contains polar moleculas and
these moleculas are free, under activity of an external field they are oriented according
to this field.
Dipole polarization has great importance in substances which moleculas have
major electrical dipole moment (in water, spirits). Moleculas of proteins and also other
high-molecular compounds owing to a dissociation of ionizable group, and also owing to
adsorption of ions have the considerable electrical dipole moments. The relaxation time
variates in limens from 10-13 s up to 10-7 s.
Time of originating of dipole polarization (relaxation time) coincides in due course
rotational displacement a molecules. The relaxation time of polar moleculas τ depends
on viscosity of medium η, temperature Т, radius of moleculas r and is calculated
approximately on a Stokes formula:
ηr 
kT
where k – is Boltzmann's constant.
Macrostructural polarization arises under action of electric field owing to a
heterogeneity of electrical properties of substances For its originating presence of layers
with various an electrical conduction is necessary.
Under activity of a field loose ions and electrons, keeping in conductive
substances, move in limits of each incorporation up to border of conducting layer. The
further travel of free charges is impossible owing to low conduction with adjacent layers.
As a result of this process conductive incorporation gets electrical dipole moment
and behaves similarly to huge polarized molecule.
The relaxation time of macrostructural polarization lays in limens 10-8-10-3 s.
Biological objects represent geterogenic structures. Heterogeneity of tissues in a
major degree is caused by presence of membranes. To them carry cellular surface
membranes and membranes, surrounding cellular organoids and forming a cytoplasmic
reticulum. If proper cell cytoplasm has small resistance because of presence in it of a
plenty of loose ions membranes have very major resistance (1000 Оm/sm2) as a result
of their small permeability for ions. Macrostructural polarization occurs in all volume of
cells, and not just on a cellular membrane as considered earlier as structure
heterogeneity is present in all volume of cells. Due to macrostructural polarization which
plays the basic role in biological objects, inductivity of tissues, measured in a constant
electric field, achieves very major quantities - up to several millions.
The surface polarization occurs on surface, having a double electrical layer.
τ  π
8
Double electrical layer is a result of heterogeneous system tendency to
diminution of a surface energy that produces an orientation of polar molecules and ions
in the surface layers therefore adjoining phases get quantity equal charges with
opposite signs.
In case of the surface polarization at superimposed an external field there is a
redistribution of ions of a diffusive part of a double electrical layer: particles of a
dispersed phase are displaced in one side, and ions of a diffusion layer - in another. As
result of it particles of a dispersed phase with counterions of a diffusion layer turn in
induced dipoles. A relaxation time of the surface polarization places in limens from 103
s up to 1 s.
Electrolytic polarization arises between the electrodes putted in electrolyte
solution, at electric current transmission through them. The relaxation time of electrolytic
polarization is measured by quantities about 10-4-102 s.
All described phenomenon of polarization to some extent are inherent in
biological objects.
At superposition of choronomic potential difference in tissues there is counterly
directional electric field which considerably reduces an external field and causes high
resistivity of tissues to a direct current (about 106-107 Оm·sm).
Thus in the beginning there are those types of polarization which have a smaller
relaxation time.
All phenomenon of polarization can be described with the help of inductivity of
substances. Inductivity ε characterizes decrease of quantity of an electric field in
substances in comparison with quantity of an electric field in empty space.
Self-control material:
B. Questions (α=ІІ)
1. Ohm's law.
2. Bridges theory.
3. The Wheatstone bridge.
4. Impedance.
5. Electical properties of biological tissues.
6. Polarisation in electrostatic field.
7. Alternationg current in biological tissues.
The subiect of the research work.
To prepare a report on the subject “Bridges theory; other bridges”.
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. –Vol.2. Basis of thermodynamics. Biomembranes.
Electricity and magnetism. – Poltava, 2014.
Additional textbook, journals and references:
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
9
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Electrodynamics. It medical use. Bases of medical
equipment.
Biophysical bases of electrocardiography.
1
medical, stomatological
Poltava – 2016
10
The topic significance:
This topic is very important, as registration of heart electric signals is one of base
diagnostic methods given to the doctors extremely valuable information.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
To form the professional experience by reviewing, training and authorizing it;
To be able to carry out laboratory and experimental work.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing disciplines):
To know concepts: electric field, potential,
physics, mathematics,
potential difference, gradient.
chemistry, biology
To describe them.
To describe membrane’s pumps work,
membrane’s permeability, rest and action
potentials
The subsequent disciplines:
To know role of electric processes in cell, tissues
Normal physiology
and whole organism functioning; generation of
electric signals of heart, them spreading in heart
and in hole body.
Materials for the before-class self-preparation work:
Theoretical questions to class:
1. Action potentials of typical and atypical heart cells.
2. Conducting system of heart; spreading of excitation.
3. Heart as a current dipole.
4. Einthoven theory
5. Standard leads, amplified leads
6. Chest leads
7. Explain shape of ECG sygnals
№
1
2
Practice work executed at class:
1. To seize habits of work with model of electrocardiographic signals generation.
2. To analyse ECG curve main waves.
3. To analyse changes of ECG curve in different leads.
Professional algorithms (instructions, reference cards) concerning
mastering habits and skills:
Task
Sequence of performance
Get familiar with the cardiograph
To study controls of represented
design, and method of using.
device, set of electrods, marks on
electrods and recording mechanism
features.
Get familiar with the model of ECGThin layer of water is filled into wide
signal formation (fig.1).
plate basin that is homogenous
electroconducting medium – model of
human body. Direct voltage source 5
supply
potential
drop
between
electrodes 1 and 2. In the position 1
stable active electrode is allocated.
Active electrode 2 can be moved to
any place in basin.
11
Electric field spreads in basin and
creates electromotive force between
electrodes 3 and 4.
Trajectory marked of three loops (P, R,
T) corresponds to oscillations of heart
electrical vector.
Electrodes 3 and 4 are stationary and
correspond to right hand and left foot
corresponds to left foot. Line between
them corresponds to axis of II lead.
Registering apparatus 6 draws curve
which corresponds to projection of
potential difference between active
electrodes 1 and 2 onto the 3–4 axis.
Value of created electromotive force
depends on visual angle and length of
1–2 electrodes distance.
3
Fig.1. Model of ECG-signal formation.
1, 2 – active electrodes; 3, 4 –
measuring electrodes; 5 – direct voltage
source; 6 – registering apparatus “КСП4”.
Use model of ECG-signal formation for
obtaining of model of ECG curve.
Contens of the topic.
12
1. Put free moved electrode 2 on the
remote (from electrode 1) position at
the QRS loop.
2. To energize device (fig.5, switcher
8).
Pointer of the “КСП-4” must move to
left, but not to the boundary of working
area. If its displacement extremely
small or pointer rest on stop, regulate
amplification of signal by the handle on
upper part of “КСП-4” (fig.5, switcher
7).
3. Switch on motor of registering
apparatus “КСП-4” (fig.5, switcher 9).
4. Move free electrod 2 along loops P,
QRS, T by direction marked by arrow
whith short (1–2 s) pauses between
outlines of loops.
Switch off motor of registering
apparatus “КСП-4” (switcher 9).
Deenergize device (switcher 8).
Analyze obtained graph.
Current dipole (dipole electrical generator)
In real condition electric dipole can not live long time: in electric field charges
begin move and dipole or will neutralized or will screened.
As current dipole can be a system, in which electric potential difference is
remained, for example, part of electric circuit, in which direct current present. On fig.2
(a)
– voltage source, r – equivalent of internal resistance of voltage source. Between
points KK current dipole is present. On fig.2 (b) R is equivalent of resistance of
conducting medium. If R<<r, current in the circuit will be constant and will not depend on
medium properties. Such double-pole system consists of spring and gutter of current
placed on small distance l is named as current dipole.
Current moment is a vector directed from positive charged pole to negative
charged pole and equal to product of current strength and distance vector l: pc=Il.
Potential drop Δφ between two field points equidistant from current dipole is
equal to:
p cos α
Δφ = c
.
4πεε 0r 2
In other words, potential drop between two field points equidistant from current
dipole in electroconductive homogenous medium is proportional to projection of dipole
moment onto the straight line which connects these points.
Electrography
All live tissues are sources of electrical potential named as biopotentials.
Electrography is general name of all biopotential registering methods that used
with research and diagnostic purposes.
Electroencephalography (EEG) is examinations of electrical activity of brain.
Electromyography is examinations of electrical activity of muscles.
Electrogastrography (EGG) – examinations of electrical activity of digestive
tract, first of all, stomach.
Electrooculography is examinations of electrical activity of eyes, where
oculomotor muscles are main search of signals.
Most used method in everyday doctor’s work is electrocardiography. The ECG
records (indirectly) the electrical activity of the heart. This activity reflects the action of
the cardiac muscle as it depolarizes and repolarizes during the cardiac cycle.
The ECG represents the temporal and spatial summation of the action potentials
of the myocardial fibers typically measured with body-surface electrodes.
ECG's are used to diagnose
arrhythmias, abnormal electrolyte (potassium,
calcium) levels, and conduction abnormalities.
They are also used for screening and therapy
guidance for heart disease as well as cardiac
gating for imaging.
In order to get an electrical signal from
the body, suitable electrodes, amplification and
A
B
appropriate display are required. Some cardiac
Fig.2. Current dipole.
cells generate action potentials (pacemakers).
Once generated, and under physiological
conditions, the action potential propagates through the cardiac muscle. The temporal
and spatial summation of the monophasic action potentials of the myocardial fibers
produces an electrical signal known as the ECG.
13
ELECTROCARDIOGRAPHY
Electrical activity of the heart
Cells within the sinoatrial (SA) node are the primary pacemaker site within the
heart. These cells are characterized as having no true resting potential, but instead
generate regular, spontaneous action potentials. Unlike non-pacemaker action
potentials in the heart, and most other cells that elicit action potentials (e.g., muscle
cells, nerve cells), the depolarizing current is carried primarily by relatively slow, inward
Ca++ currents instead of by fast Na+ currents (fig.3). There are, in fact, no fast Na+
channels operating in SA nodal cells. Na+ enter node cells through opened Ca++
channels. This results in slower action potentials in terms of how rapid they depolarize.
Therefore, these pacemaker action potentials are sometimes referred to as "slow
response" action potentials.
A
B
Fig.3. Ion currents in various periods of action potential of
pacemaker (A) and working myocardiocyte (B).
Phases: 1 – depolarization, 2 – initial fast repolarization,
3 – slow repolarization, 4 – ended repolarization, 5 – rest.
If – Na+ “funny” current, IСa – Ca++ currents, IK – K+ current. INa – fast Na+ current.
SA nodal action potentials are divided into three phases. Phase 5 is the spontaneous
depolarization (pacemaker potential) that triggers the action potential once the
membrane potential reaches threshold between -40 and -30 mV). Phase 1 is the
depolarization phase of the action potential. This is followed by phase 4 repolarization.
Once the cell is completely repolarized at about -60 mV, the cycle is spontaneously
repeated.
The changes in membrane potential during the different phases are brought about by
changes in the movement of ions (principally Ca++ and K+, and to a lesser extent Na+)
across the membrane through ion channels that open and close at different times during
the action potential. When a channel is opened, there is increased electrical
conductance (g) of specific ions through that ion channel. Closure of ion channels
causes ion conductance to decrease. As ions flow through open channels, they
generate electrical currents that change the membrane potential.
In the SA node, three types of ions are particularly important in generating the
pacemaker action potential. The role of these ions in the different action potential
phases are illustrated in the fig.3 and described below:
– At the end of repolarization, when the membrane potential is very negative
(about -60 mV), ion channels open that conduct slow, inward (depolarizing) Na+
currents. These currents are called "funny" currents and abbreviated as "If". These
14
depolarizing currents cause the membrane potential to begin to spontaneously
depolarize, thereby initiating Phase 5. As the membrane potential reaches
about -50mV, opening of Ca++ channels support continuing depolarization up to
threshold level just as a fall in K+ conductance.
– Phase 1 depolarization is primarily caused by increased Ca++ conductance (gCa++).
Because the movement of Ca++ through these channels into the cell is not rapid, the
rate of depolarization (slope of Phase 1) is much slower than found in other cardiac
cells (e.g., Purkinje cells).
– Repolarization occurs (Phase 5) as K+ channels open (increased gK+) thereby
increasing the outward directed, hyperpolarizing K+ currents. At the same time, Ca++
channels close, gCa++ decreases, and the inward depolarizing Ca++ currents
diminish.
During depolarization, the membrane potential (Em) moves toward the equilibrium
potential for Ca++, which is about +134 mV. During repolarization, gCa++ (relative Ca++
conductance) decreases and gK+ (relative K+ conductance) increases, which brings Em
closer toward the equilibrium potential for K+, which is about -96 mV).
Although pacemaker activity is spontaneously generated by SA nodal cells, the rate of
this activity can be modified significantly by external factors such as by autonomic
nerves, hormones, drugs, ions, and ischemia/hypoxia.
It is important to note that action potentials described for SA nodal cells are very similar
Fig.4. Ion currents in various periods of action potential of pacemaker
at various heart contraction frequencies.
a – maximal frequency, c – minimal frequency.
to those found in the atrioventricular (AV) node. Therefore, action potentials in the AV
node, like the SA node, are determined primarily by changes in slow inward Ca++ and K+
currents, and do not involve fast Na+ currents. AV node action potentials also have
intrinsic pacemaker activity produced by the same ion currents as described above for
SA nodal cells. Spontaneous frequency of AV nodal cells is lower than SA node
frequency.
Changing of heart work frequency is realized due to changing of rate of initial slow
depolarization (fig.4).
Transformation of non-pacemaker into pacemaker cells
It is important to note that non-pacemaker action potentials can change into pacemaker
cells under certain conditions. For example, if a cell becomes hypoxic, the membrane
depolarizes, which closes fast Na+ channels.
At a membrane potential of about –50 mV, all the fast Na+ channels are inactivated.
When this occurs, action potentials can still be elicited; however, the inward current are
carried by Ca++ (slow inward channels) exclusively. These action potentials resemble
those found in pacemaker cells located in the SA node, and can sometimes display
spontaneous depolarization and automaticity. This mechanism may serve as the
15
electrophysiological mechanism behind certain types of ectopic beats and arrhythmias,
particularly in ischemic heart disease and following myocardial infarction.
Conducting system of heart.
Cardiac cycle
The sinoatrial (SA) node, is the
pacemaker of the heart. These special
autorhythmic cells initiate the action
potentials that cause contraction. They
start the action potential spreading
through the atria.
Particular cells (similar to SA node cells
by some properties) form conduction
tracts in atria.
Excitation of working myocardiocyte
begins after arrival of electric excitation
wave (ionic currents which call change
of electric potential and opening of ionic
– Na+ – channels) from adjacent
conductions or working cells.
The atrioventricular (AV) node, at the
base of the septum, allows the signal
started by the SA to spread to the
ventricles after delay, which is
necessary for atria full contraction and
filling ventricles by blood.
The bundle of His (atrioventricular
Fig.5. Heart conducting system.
bundle, atrioventricular fascicle) starts at
the AV, divides into left and right
peduncles which follow the septum and curve around to the outer walls. Left peduncle
slightly below divides into anterior and posterior peduncular branches. Purkinje fibers
extend from the bundle of His. These help spread the action potential rapidly through
the ventricle. Velocity of excitation spreading by His bundle and its branches is maximal
in heart and near to 5 m/s.
All these elements (SA node, AV node, conduction tracts) are conducting system of a
heart which supports correct, high effective alternation of hearth chambers contractions.
As result of coherent work it is observed coherent blood flows and maximal possible
effectiveness of heart work On fig.7 you can see generation and spreading of excitation
over conducting system and myocardium, change of heart chambers shape and filling.
16
Excitated areas are shown by more bright color. 1 – period of slow filling (heart rest); 2 –
appearance of excitation in SA-node; 3 – blood during contraction is pumped from both
atria’s into ventricles, excitation is delayed in AV-node;
4 – blood after contraction filled both ventricles; 5 – excitation streams along His bundle
and envelops adjacent areas of the septum, as result apex of heart drag upward; 6 –
excitation envelops apex of heart, blood begins arrive to aorta and pulmonary artery; 7 –
excitation envelops cardiac wall, full ventricles contraction develops, blood outflow
increases; 8 – excitation envelops base of ventricles too, blood outflow reduces, blood
begins to arrive into atriums from veins; 9–10 – excitation deceases – repolarization is,
blood outflow ends, blood entrance increases; 11–12 – new period of slow filling (heart
rest).
Cardiac Vector
The cardiac vector indicates the average direction of the depolarization in time (fig.8–
10). The ECG measured from any one pair of the bipolar leads is a time variant, single
dimensional projection of the cardiac vector and could be represented using the
Einthoven triangle. Willem Einthoven was a Dutch physiologist who pioneered the ECG
Fig.7. Heart contraction stages.
17
and won the Nobel prize in
Medicine in 1924 for this work.
Typically, the QRS segment is
represented in the triangle.
ECG Acquisition
The electrodes are traditionally
placed on arms and legs, making
it easy to position the electrodes.
These connections are called
leads.
Changes of a potential difference
on the body surfaces arising in a
work time of a heart are
registered with the help of various
systems of electrocardiogram
leads. Each lead registers the
potential difference existing
between two certain points of
Fig.8. Heart electric dipole in time moment, when
heart electric field in which
dipole moment is maximal;
electrodes are established. Thus,
it is correspond to maximal value of R wave.
various electrocardiographic
leads differ among themselves first of all body
sites from which the potential difference is
allocated.
The electrodes established in each chosen points
on a body surface, are connected to a
galvanometer of electrocardiograph. One of
electrodes attach to a positive pole of a
galvanometer (it is positive, or active, an electrode
of lead), the second electrode - to its negative pole
(a negative electrode of lead) (fig. 11).
Fig.9. Formation of average electric
dipole vector.
Now in clinical practice most
widely use 12 leads of an
electrocardiogram which
record is obligatory at
everyone
electrocardiographic
inspection of the patient: 3
standard leads, 3 amplified
(strengthened) unipolar
leads from finitenesses and
6 chest leads (fig. 12).
Fig.10. Formation of ECG main waves.
18
Fig.11. The standard II lead:
registration mode.
The standard bipolar leads offered in 1913.
Einthoven, fix a potential difference between two
points of an electric field removed from heart and
located in a frontal plane - on limbs. For record of
these leads electrodes impose on the right hand (red
marks), the left hand (yellow marks) and on the left
leg (green marks) (see fig.12). These electrodes are
in pairs connected to electrocardiograph for registration
of each of three standard leads. The fourth electrode
is placed on the right leg for connection grounded wires
(black marks).
Marks (+) and (–) here designate corresponding
connection of electrodes to positive or negative poles
of a galvanometer, i.e. are specified a
positive and negative pole of each
lead.
Apparently on fig. 13, three standard
leads the left hand and the left leg
with the electrodes established there
form an equipotential triangle
(Einthoven’s triangle) which tops are
the right hand. In the center of
equipotential Einthoven’s triangle the
electric center of heart, or the dot of
dotted sole heart dipole equidistant
from all three standard leads is
located.
The hypothetical line connecting two
Fig.12. Registration of 12-lead ECG.
Fig.13. Three-axial system of coordinates of standard leads. Thick lines
show axes of three standard leads from finitenesses in Einthoven’s triangle (а)
and in three-axial system of coordinates (b).
electrodes, participating in formation of electrocardiographic leads, refers to as an axis of
19
lead. Axes of standard leads are the sides of Einthoven’s triangle (see fig. 14). The
perpendiculars which have been draw from the center of heart, i.e. from the location of
sole heart dipole, to an axis of each standard lead, divide each axis into two equal
parts: positive, directed to the side of a positive (active) electrode leads (+), and
negative, directed to a negative electrode (–). If electromotive force of hearts during any
moment of heart cycle it is projected on a positive part of an axis of lead, on an
electrocardiogram the positive deviation (positive waves P, R, T) enters the name. If
Fig.15. The standard leads:
I Right arm (-), Left arm (+)
II Right arm (-), Left foot (+)
III Left arm (-), Left foot (+)
electromotive force of hearts it is projected on a negative part of an axis of lead, on an
electrocardiogram negative deviations (waves Q, S, sometimes negative waves T or
even Р) are registered.
For simplification of the analysis of the electrocardiograms registered in standard leads,
and acceleration of operation of decomposition of vector of heart electromotive force in
Fig.16. Forming of amplified leads with them axes.
electrocardiography it is accepted to displace some axes of these leads as it is shown
on fig. 1.3, and to carry out them through the electric center of heart. The three-axial
20
system of coordinates convenient for the further analysis in which the corner between
axes of each lead makes, as well as in traditional Einthoven’s triangle, 60 ° turns out.
Such small displacement of axes of standard leads is quite competent, as at moving
axes in parallel their initial arrangement the projection to them of a heart vector does not
change.
The standard leads are: I, II and III (fig.15).
Amplified leads and chest leads have a single positive electrode and uses
combination of other electrodes as a composite negative electrode; they have
conventional name unipolar leads.
Amplified (strengthened) leads from limbs
Amplified leads from limbs have been offered by Goldberger in 1942. They register a
potential difference between one of limbs on which the active positive electrode of the
given lead (the right hand is established, the left hand or the left leg), and average
potential of two other limbs (fig. 10.20). Thus, as a negative electrode in these leads
use so-called joint (incorporated) Goldberger’s electrode which is formed at connection
through additional resistance of two limbs.
Remember! Three amplified unipolar leads from limbs designate as follows: aVR amplified lead from the right hand; aVL - amplified lead from the left
hand; aVF - amplified lead
electromotive
from the left leg.
force
The designation of amplified leads from finitenesses occurs from the first letters of the
English words: "a" - augmented (amplified); "V" - voltage (potential); "R" - right; "L" –
left; "F" - foot.
Apparently on fig.16, axes of amplified unipolar leads from finitenesses receive,
connecting the electric center of heart with a place of imposing of an active electrode
of the given lead, т. е actually - from one of tops of Einthoven’s triangle.
Fig.17. All 6 frontal axes, them directions and angles.
The electric center of heart as though divides axes of these leads into two equal parts:
positive, inverted to an active electrode, and negative, inverted to incorporated
Goldberger’s electrode.
Electrical axis of heart is vector that coincides with heart electric dipole in time
moment, when dipole moment is maximal (see fig.8). Usually it manifests in maximal R
wave in corresponding axis. In other cases it position calculated as algebraic sum of two
largest neighboring R waves (need remember that aVR vector is used with opposite
direction in this action).
Electrical axis of heart lays in norm between +20°–+70° and is displayed in maximal R
wave in II standard lead. Levocardiogram is case when electrical axis lies at angle less
than +20°; usually R wave in I standard lead is greatly more than R wave in III standard
21
lead. It can be at horizontal position of the heart, left ventricular hypertrophy and so on.
Dextrogram – electrical axis lies at angle more than +70°. It causes can be vertical
position of the heart, right ventricular hypertrophy and so on.
Chest leads
The chest unipolar leads offered by Wilson in 1934, register a potential difference between
the active positive electrode located in certain points on a surface of a chest, and
Wilson negative unified electrode.
Last is formed at connection through additional resistance of three finitenesses (the
right hand, the left hand and the left leg), the incorporated which potential is close to
zero (about 0,2 mV).
Usually for record of an electrocardiogram use 6 standard positions of a chest
electrode on a forward and lateral surface of a chest which in a combination to Wilson
unified electrode form 6 chest leads (fig. 18, 19).
Wilson unified electrode is formed by 3 electrodes: on hands and left leg, connected
together. It allow to comparison potentials of chest surface to average potential of body
frontal plane. Chest leads are designated by header Latin letter V (potential, voltage)
with addition of number of a position of the active positive electrode designated in the
Arabian figures.
Lead V1 - the active
electrode is established in
the fourth intercostal place
by a right edge of a breast.
Lead V2 - the active
electrode is located in the
fourth intercostal place by a
left edge of a breast.
Lead V3 - an active electrode
is between the second and
fourth position,
approximately at a level of
the fourth edge on left
parasternal lines.
Lead V4 - the active
electrode is established in
the fifth intercostal place on
left median-clavicular lines.
Lead V5 - the active
Fig.18. An arrangement of 6 electrodes of chest leads on chest
electrode is located at the
surface (horizontal plane).
same horizontal level, as V4
on the left forward axillary line.
Lead V6 - an active electrode is on the left average axillary line at the same horizontal
level, as electrodes of leads V4 and V5.
Electrocardiographs are used in medicine for recording of biological potentials,
which are generated by myocardium. Einthowen offered a simple model for
exposition of these electrical appearances.
A complex sequence of depolarization and repolarization of hart cells membranes
can be described in a simplified way with a vector of dipole momentum (D). This
vector changes its length and orientation during the cardiac cycle.
According to Einthoven's theory, there is a relation between the dipole momentum
and electric potential differences on the body surface. These potential differences are
usually measured between the following points: the right arm (RA), the left arm (LA), and
22
the left leg (LL). The potential difference registered between two points on the body
surface is referred as "lead". Leads I ( LA -RA), II ( RA - LL ), III ( LL - LA ) are
"standard leads".
Now in clinical practice most widely use 12 leads of an electrocardiogram which
record is obligatory at everyone electrocardiographic inspection of the patient: 3
standard leads, 3 amplified (strengthened) unipolar leads from finitenesses and 6
chest leads.
For record of these leads electrodes impose on the right hand (red marks), the
left hand (yellow marks) and on the left leg (green marks). These electrodes are in
pairs connected to electrocardiograph for registration of each of three standard leads.
The fourth electrode is placed on the right leg for connection grounded wires (black
marks).
A curve of the potential differences in the leads against the time during a cardiac
cycle is named the electrocardiogram (ECG, in some American literature also EKG).
A normal ECG in the standard lead II looks like it is shown in Fig.19.
The wave P characterizes formation of
an action potential in the hart auricles. The
complex QRS is related to excitation of
ventricles of heart. The wave T
corresponds to repolarization of the
myocardium cells.
During a cardiac cycle the vector of
the dipole momentum makes three
Fig. 19. Model of electrocardiogram.
revolutions. The duration of the interval P-T
is equal to 0.3 s; the peak amplitude (wave R) is about a millivolt (potentials
generated inside the hart are about 100 times higher). A deviation of ECG
parameters from standard ones is an evidence for heart pathologies.
A deviation of ECG parameters from standard ones is an evidence for heart
pathologies.
E
IDC
FF
A
R
E
Fig. 20. Scheme of an electrocardiograph.
The device for recording ECG is an electrocardiograph. An elementary singlechannel electrocardiograph consists of four basic parts (see Fig. 20): electrodes (E),
input device communicator (IDC), frequency filter (FF) amplifier (A) and a recording
device (R). General scheme of electrocardiograph connection to patient look at fig.21.
Depending on accuracy of the signal recording, electrocardiographs are
classified into three classes. Devices of the 1st class are the most precise. They
ought to record signals in a frequency range up to 800-1000 Hz without distortion. The
devices of the 2nd class have one or two canals and the highest frequency of recorded
oscillations of 70-100 Hz. The devices of the 3rd class record oscillations till 60-70 Hz.
Electrocardiographs of the latter class have small size and mass.
Typical basic specifications of the electrocardiograph are the following:
Measurable voltage range: 0.1-4 mV,
Recorded voltage range: 0.03-5 mV,
Sensitivity: 5, 10, 20 mm/mV,
Effective width of record: not less than 40 mm,
Paper tape velocity: 25 and 50 mm/s,
23
Electrosafety: class II, type BF
Fig.21. Electrocardiographic device.
ECG Nominal Data
Nominal range of amplitudes of electrocardiographic waves (mV)
Wave amplitudes
Lead I
Lead II
Lead III
P
0.015 to 0.12
0.000 to 0.19
-0.073 to 0.13
Q
0.0 to 0.16
0.0 to 0.18
0.0 to 0.28
R
0.02 to 1.13
0.18 to 1.68
0.03 to 1.31
S
0.0 to 0.36
0.0 to 0.49
0.0 to 0.55
T
0.06 to 0.42
0.06 to 0.55
0.06 to 0.30
Nominal ECG interval durations
Average
Range
PR interval
0.18
0.12–0.20
QRS duration
0.08
0.07–0.10
QT interval
0.40
0.33–0.43
ST interval (QT minus QRS)
0.32
24
When it is necessary to trace heart rhythm of
patient, for example in case of state, when
periodically dangerous attacks of heart arrhythmia
happen. Other example is research of working
conditions of heart at different states and under
loadings. In this case monitoring of ECG must be
used. It is light device with electrodes fasted on
body (fig.22).
Fig.22. Monitoring of ECG.
Self-control material:
B. Test tasks (α=ІІ)
1. What types of biological potentials exist:
A) Oxidation-reduction potentials;
B) Potential of sedimentation;
C) membranous potentials;
D) Potential of current.
2. For what chest leads are used at
electrocardiography:
A) For amplification of a signal;
B) For correction of the standard leads data;
C) For grounding;
D) For registration of an electric vector behavior
in frontal plane.
3. To what process in heart there corresponds
QRS complex:
A) Excitation of auricles;
B) depolarization of ventricles;
C) repolarization of ventricles;
D) depolarization of auricles.
4. Electrogramme is a dependence on time of:
A) Potential differences which arises at passage
of an electric current through the certain site of a
living tissue;
B) Potential differences which arises at
functioning the certain органа;
C) a living tissue electrical conduction which
changes owing to blood supply changing;
D) Potential differences which arises at
functioning of certain tissue.
5. Where there is a pacemaker of heart
contractions?
A) Sinus node;
B) atrioventricular system;
C) His bundle;
D) The left auricle.
6. What are amplified leads?
A) leads use as negative electrode connection
with right hand;
B) leads use device with special amplifying
circuit;
C) leads use as negative electrode which is
formed at connection through additional
25
resistance of two limbs;
D) leads use as negative electrode connection
with chest.
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009. – 1–2 vol.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. –Vol.2. Basis of thermodynamics. Biomembranes.
Electricity and magnetism. – Poltava, 2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
26
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Electrodynamics. It medical use. Bases of medical
equipment.
Medical equipment. Devices for medical-biological
information pickup.
1
medical, stomatological
Poltava – 2016
27
The topic significance:
Sensor (measuring converter, transducer, data unit, sensing element, monitor,
sensing unit, transmitter) is part of measurement device that directly communicate with
object of examination and transform measurand [measured quantity] into form easy-touse of researcher; generally it is electric signal which is passed, processed,
represented, measured or registered next.
Most often measurand is physical quantity (pressure, displacement, temperature,
voltage and so on). Further only sensors with electrical output signal [pickup signal] will
be considered.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
To know electrodes classifications, general demands to electrodes, demands to
biomedical electrodes, methods of use in medicine.
To know sensores classifications, physical principles of different sensores.
To know general demands to sensores, demands to biomedical sensores,
methods of use in medicine.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Previous (providing
Obtainable skills
disciplines)
Physics
To define basic concepts of physical parameters: pressure,
sound intensity, resistance, conductivity, capacitance,
inductance, temperature, illuminance, optical spectrum and
them interrelations.
To know measurement units of physical quantities.
Materials for the before-class work self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Biomedical
Biosensors are sensors used for reception of information on
sensor
functioning alive organisms, their organs and systems.
Electrode
conductor of the special shape and construction with which help the
explored field of a body or an organ of an alive organism is connected
in an electric circuit of the measuring device
Sensibility
minimal change of measured parameter which can be steady detected
Dynamic
range of input quantities in which measurement is carried out without
range
significant errors
Accuracy
maximal difference between obtained and nominal output values
Response
minimal time range during that output value reach the level
time
corresponding to level of input parameter
Reproducibility difference between output signals on equal input influences in different
time moments must be absent
Requirements – reception of an steady informative signal (functionally reliable);
for biomedical – minimum of distortions of the useful signal;
sensors
– maximum noise immunity;
– convenience of use and arrangement;
– absence of the side influences on an organism (safety); construction
of the sensor contacting to a body (in vivo applications) must be
nontoxic and nonthrombogenic;
28
– opportunity of sterilization (for sensors of reusable use);
– low cost (for sensors of unitary use).
Theoretical questions to class:
1. Classifications of sensors (electrodes and transducers; in dependence on the
quantity to be measured; bio-controlled and energy; according to physical nature of
input signal).
2. Requirements for biomedical sensors.
3. Metrological characteristics of sensors.
4. Electrodes types.
5. Requirements to electrodes of medical and biologic purposes.
6. Electrodes classification.
7. Mechanical measurement sensors.
8. Magnetic measurement sensors.
9. Temperature measurement sensors.
10. Optical Biosensors.
11. Piezoelectric transducers.
Content of the topic.
Sensor (measuring converter, transducer, data unit, sensing element,
monitor, sensing unit, transmitter) is part of measurement device that directly
communicate with object of examination and transform measurand [measured quantity]
into form easy-to-use of researcher; generally it is electric signal which is passed,
processed, represented, measured or registered next.
Most often measurand is physical quantity (pressure, displacement, temperature,
voltage and so on). Further only sensors with electrical output signal [pickup signal] will
be considered.
Biosensors (biomedical sensors, biomedical transducers) are sensors used
for reception of information on functioning alive organisms, their organs and systems.
All measured biomedical parameters can be divided into two groups: directly
measured and mediately measured. Mediately measured parameters are that can’t be
measured or that can be measured hardly or with the risk to healthy or uncomfortable. If
they influence on other parameters more comfortable for measuring, and these other
parameters are measured, we tell about mediately measuring.
Examples of directly measured parameters are motions of extremities and chest,
body temperature, biopotentials, body pressure in blood vessel. Examples of mediately
measured parameters are blood pressure (by sounds in time of blood flow), oxygenation
of hemoglobin by spectral characteristics of blood by light transmission of tissues and
further.
Sensors designed for medicine (biosensors) use must to meet the next
requirements:
–
reception of an steady informative signal (functionally reliable);
–
minimum of distortions of the useful signal;
–
maximum noise immunity;
–
convenience of use and arrangement;
–
absence of the side influences on an organism (safety); construction of the
sensor contacting to a body (in vivo applications) must be nontoxic and
nonthrombogenic;
–
opportunity of sterilization (for sensors of reusable use);
–
low cost (for sensors of unitary use).
Additional issues are the long term biocompatibility of the sensor.
29
Output electrical signal of sensor can be: current, voltage, impedance, frequency
of phase of alternating current or pulse signals.
Classifications of sensors
1). Biomedical sensors are divided on two groups: electrodes and proper sensors
(transducers).
Biomedical sensors are classified in dependence on the quantity to be measured:
– electrical;
– mechanical (linear and angular displacement, pressure, velocity, acceleration,
frequency of oscillations,…);
– physical (temperature, illuminance, sound intensity, humidity,…);
– physiological (filling of tissue by blood);
– chemical (concentration of certain ions, activity of ions,…).
2). Biomedical sensors can be bio-controlled and energy.
Bio-controlled sensors can be generator (active) or parametric (passive).
Parametric sensors change own electrical parameters (resistance, capacitance
or inductance) under the influence of measured object.
Generator sensors directly transform energy of input signal into electrical output
signal that is they generate corresponding signal. Some types of such sensors are: a)
piezosensors or piezoelectric transducers, b) thermoelectric transducers, c) induction
sensors used electromagnetic induction, d) photoelectric sensors.
Energy sensors are complex: firstly, part that influence of the organs and tissues
and, secondly, proper sensor. Energy flux of influence has strict characteristics;
measured parameter changes these characteristics, modulate them. Examples of such
equipments are ultrasound and photoelectrical sensors.
Metrological performances of sensors:
1) sensibility (sensitivity resolution) – minimal change of measured parameter
which can be steady detected; it shown as z = Δy/Δx, where Δy – change of output
signal at change of input value Δx, and measured thereafter in Ω/mm (Ohm per
millimeter) or mV/K (millivolt per Kelvin) and the like;
2) dynamic range (operating range) – range of input quantities in which
measurement is carried out without significant errors;
3) accuracy – maximal difference between obtained and nominal output values;
4) response time (response speed) – minimal time range during that output
value reach the level corresponding to level of input parameter;
5) reproducibility – difference between output signals on equal input influences
in different time moments must be absent.
Next terms are used often:
transducer gage – measuring device with converter;
transducer-converter – sensor- converter;
transducing apparatus – converter, device for converting.
Artefact - process or the formation not peculiar to an object of interest and
incipient during examination. They distort obtained information and often are result of
mistakes at matching or fulfilling of investigation method or sensors. For example, when
substance of sensor interacts chemically with investigated object. Struggle against
undesirable influences and artefacts is important and obligatory side of investigations.
According to physical nature of input signal sensors are divided on: mechanical,
acoustical (sound), optical and so on.
Electrical measurement
(include biopotential measurements)
Electrodes are conductors of the special shape and construction with which help
the explored field of a body or an organ of an alive organism is connected in an electric
circuit of the measuring device. More often they use at electrocardiographies (ECG),
30
electroencephalography (EEG), electromyography (EMG), electro-oculography, electrogastrography (EGG), rheography (REG).
Electrodes use also for electrical action on an organism from the outside, for
example, at medicinal electrophoresis, at rheography, at physiotherapeutic treatment by
pulsing currents, at using the device "electrodream".
Separately it is necessary to view the microelectrodes used for pickup of
electrical signals or electrical action at a level of separate cells and cellular ensembles.
Requirements to electrodes of medical and biologic purpose:
– are promptly fixed and removed;
– high stability of electrical parameters, absence of artefacts and noises;
– low losses of an electrical signal, including small transition resistance in zone of
contact to object;
– mechanical strength;
– absence of irritant action;
– low price.
Particularly strict requirements are made to implanted electrode, which must work
long time (many years in case of heart control).
When a metal is placed in an electrolyte (ionizable solution), an uneven charge
distribution is created at the metal/electrolyte interface. The charge distribution causes
an electric potential across the interface between the metal and the electrolyte. In more
details these processes are described in the chapter "Electrokinetic phenomena". As
result of these processes chemical change of the material of electrodes and studied
object, irritation of tissue, errors of measured signals can be observed.
Hydrogen is the standard half-cell potential. Stronger oxidizing agent have more
potential (F2>Cl2>Ag>Cu>H2), weaker oxidizing agent have less potential
(Li<Mg<Zn<Pb<H). For example, standard reduction potential at 25ºC for H equal to
0 V, for Ag 0,8 V, for Zn –0,76 V. It’s mean that if used two electrodes – Ag and Zn – in
one vessel with electrolyte, electric potential arises between them equal to 1,56 V.
The transient resistance "electrode - skin" can achieve hundreds kiloohms at a
dry clean skin. It depends on properties of a skin, such as metal of which the electrode
is made, contacting areas and a conducting medium between a skin and an electrode.
For diminution of the transient resistance the napkins imbued by a normal (physiologic)
saline solution, or more effective special conductive electrode pastes (electroding ink)
are used.
The major contacting area provides diminution of resistance, however gives in
distortions of a registered signal.
To manufacturing electrodes apply gold, platinum, iridium, tungsten, argentum,
palladium, stainless steel of a special composition, alloys with iridium, etc. Frequently
use the argentum electrodes coated by very thin layer of chloride argentums (Ag/AgCl
electrodes). The exact selection of metal and structure of the surface stratum of an
electrode, use of special electrode pastes allows to lower transient resistance and
effects of polarization too.
Tungsten is the most versatile and widely used probe material because of ifs
stiffness, biocompatibility and cost. It is ideal for most recording and electro-stimulation
purposes.
Platinum/iridium are extremely inert and is much more resistant to corrosion than
either tungsten or stainless steel when used in long time stimulation examinations.
Stainless steel is widely used due to its stiffness and it can be easily
electrochemically coated with other metals used in certain type of studies.
Pure iridium has by far the lowest concomitant tip impedance of any of the noble
metals. It is extremely inert and very resistant to corrosion.
31
Construction and performances of electrodes depend on the purposes of
application. To destination electrodes part on 4 groups:
1) For disposable application (for the functional diagnostics).
2) For the long-lived continuous observation (reanimation, intensive therapy).
3) For dynamic application (sports medicine, the check of a patient state in time of
sports rehabilitation).
4) For emergency application.
Main shapes of electrodes:
1) electrode plate;
2) vacuum cup (sucker);
3) olive at the ending of rubber or plastic catheter (used for esophageal
registration of ECG);
4) piercing (needle-type, acicular, trocar) electrode;
5) multipoint electrode;
6) capacitive pickup electrode;
7) snare (electrode with loop shape – active electrode).
Microelectrodes
Biopotential electrodes with an ultra-fine tapered tip are used that can be inserted
into individual biological cells. Commonly used in neurophysiology studies.
The tip of these electrodes must be small with respect to the dimension of the
biological cell wall.
Kinds of microelectrodes:
1) glass micropipette;
2) metal microelectrode;
3) solid-state microprobes.
Intra-operative electrod microelectrodes es can be available in Tungsten and
Platinum/Iridium core conductors covered by polymer insulator. Length of free tip can be
equal from 5 mm (electrodes for work with neuronal pools) to 5 μm (electrodes for work
with separate cells), thickness of covered layer can reach 1 μm.
Mechanical measurement
Sensors which are used for measuring of displacement (stretching or contraction)
term as strain gages (strain indicator, strain sensor). Devices used strain gages term as
tensometers (extensometer, strainometer). These names are used for pressure sensors
too, since object of measuring in both cases the same: displacement of sensor parts.
Displacement transducers (position transducer)
Potentiometer transduces linear or angular displacement into a voltage. When a
moving contact of variable resistor move, resistance between it terminals change; taked
off voltage changes correspondingly.
Elastic resistive transducers
l
R
S , where ρ – resistivity constant
Resistance of electric conductor equal:
(specific resistance) of material, l – length of resistor, S – cross-section area of resistor.
If resistor is elastic (can stretch and restore after removing of stretching force),
during the elongation cross-section area decrease.
Such sensor used for measuring of amplitude and frequency of respiratory
movements and for plethysmography (research of blood supply changing).
For example, elastic transducer is wrapped around the chest. The chest diameter
during exhalation is 33 cm; corresponding circumference is near 104 cm. During
inspiration volume and circumference increase, length of transducer increase, and its
resistance increase too.
Strain gauges
Gauge insensitive to lateral forces
32
It’s used in blood pressure transducers. Change in resistance is quite small.
Inductive displacement transducers (variable-reductance transducer)
Inductive displacement transducer or LVDT sensor (linear variable displacement
transducer, linear voltage differential transformer).
When the core moves towards one coil the voltage induced in that coil increases
proportionally.
n2 S
Inductance of solenoid L   0
, where n – coil turns, μ – relative magnetic
l
permeability of the core material, μ0 – absolute magnetic permeability of vacuum, l –
solenoid length, S – cross-section area of solenoid.
Semiconductor strain gages are used for measuring of pressure.
Capacitors and capacitive transducers
The most common method to measure displacement is to change the plate
separation distance d.
This arrangement can be used to measure force, pressure or acceleration.
S
The capacitor capacitance is equal: C   0 , where S – the area of a plate
d
(armature) of the condenser; d – distance between plates; ε – an inductivity of medium
between plates; ε0 – absolute inductivity of vacuum.
If the distance between plates varies, the capacity varies inversely.
They are used to measure respiration or movement studies (when placed on a
mat). Capacitance sensors can measure ranges up to 300 nm with 0,1 nm resolution.
Piezoelectric transducers
Piezoelectricity – is originating of electrical charges displacement at strain of a
crystal (direct piezoelectric effect). If the crystal is mechanically strained, it generates a
small potential.
Inverse piezoelectric effect is a strain of a crystal under activity electric field in
case an electric field is applied across its plates.
Crystal contracts in direction perpendicular to direction of applied electric field and
turn, direction of originated electric field is perpendicular to direction of compression.
Piezoelectric sensors are active bio-controlled sensors.
Piezoelectric properties are observed at some kinds of monocrystal (native or
artificial), for example, quartz, and at artificial materials as piezoceramics and
piezopolymers. On the figure flexible polymer sensor is observed.
Piezoelectric sensor of simplest type is piezoelectric plate squeezed between two
metal facings.
Used widely in different – all – branches of science and techniques.
They are used in cardiology to listen to heart sounds (phonocardiography), to
automated measure of blood pressure, physiological forces and acceleration
measurements. Also they are employed as sources of sound and supersonic signals.
High frequency-sound waves greater than 20 KHz due to inverse piezoelectric effect.
Modern microphones used for studying of heard sounds are piezoelectric.
Sometimes used electrodynamic microphones in which inductance coil bound with
elastic membrane moved in static magnetic field under the influence of variable electric
current through coil that originates variable magnetic field in coil.
Using magnetic fields
Blood flow through an exposed vessel can be measured by means of an
electromagnetic flow transducer.
The probe contains coils that produce an electromagnetic field transverse to the
direction of blood flow.
33
The electric charges in blood (the anions and the cations) experience force
induced by the presence of the magnetic field. F = qvB, where F – induced force, q –
charge of particle, v – velocity of charge, B – inductance of magnetic field.
Charge of electron q = –1,602•10–19 C; it is equal to absolute value of positive
monovalent ion as Na+ or K+.
Oppositely charged particles move in opposite directions this movement causes
an opposing force: Fop = qE = qV/d, where V – voltage formed consequently, d –
diameter of vessel.
At equilibrium qV/d = qvB => V/d = vB, therefore v = V/dB. Here V – measured
value.
Temperature measurement
It is the most often controlled physiological values and one of the four basic vital
signs.
Distinguish temperature of nucleus (core) of a body and temperature of body
surfaces – skin.
Inner (core) temperature is remarkably constant (37±0,5ºС). Temperature of the
skin changes in more wide limits. If slightly dressed person is in room with normal
conditions – 20ºС, temperature is equal to 36,6ºС in armpit, rectal temperature – 37ºС,
and lower at other skin areas (in the center of footstep 27–28°C), particularly on open
sites of extremities. Temperature is measured routinely in contact with the skin or inside
a body cavity. At measuring the surface temperature it is important to estimate
symmetry of temperature allocation that corresponds to norm and reflects intensity of a
blood supply of a body fields, and also presence possible inflammatory or neoplastic
processes. Temperature of a skin influence also a state of a surrounding medium
(temperature, air humidity), tone of vegetative nervous system, a body hair
development, clothes.
Temperature sensors are:
–
wire-wound termoresistors;
–
semiconductor-resistance thermometers;
–
difference thermoelements.
Thermistors (termoresistors ) – require direct contact with skin or mucosal
tissues. They can be made of compressed, sintered metal oxides (Ni, Mg, Co) or
semiconductors that change their resistance with temperature. Sensitive element of
device is small to produce a rapid response. Shapes of sensor are difference from
needle to flat.
Non contact thermometers used for determination of body core temperature inside
the auditory canal as temperature of temperature of ear canal near the tympanic
membrane is known to track the core temperature.
Noncontact thermometer
Temperature of the ear canal near the tympanic membrane is known to track the
core temperature very accurately – by 0,5–1ºC. Infrared radiation from the membrane is
channeled to a thermopile detector through a metal waveguide. Thermopile converts
heat flow into current.
Next step of distant thermometry are thermovision or thermography. Sensors
convert the infrared radiation into electrical signals. For more details see chapter
“Thermal radiation”.
Optical Biosensors
Usually as optical sensor are used photoresistors (for more details see chapter
“Interaction between light and tissue“), which change resistance under the influence of
incident light.
34
Arterial blood gases
Blood changes its color depending on the amount of oxygen bound to the
hemoglobin in the erythrocytes. Oxygenated arterial blood is light red; vein blood is dark
red with shifted spectral maximum of optical transmission.
Normal physiological conditions 98% of the total amount of oxygen is contained in
the erythrocytes in a loose combination of hemoglobin Hb and oxyhemoglobin Hb02.
The remaining 2% of oxygen is dissolved in the blood plasma. Oxygen saturation (SO2)
is the relative amount of oxygen carried by the hemoglobin in the erythrocytes. During
oximetry SO2 is determined.
Oximetry is based on the light absorption properties of blood and on the relative
concentration of hemoglobin (dark-red) and oxyhemoglobin (red).
Measurement is based on Beer-Lambert's law that relates absorption of light to
the properties of the material through which the light is transmiting.
Electronic circuits turn on and off sequentially the LEDs (light-emitting diodes) and
synchronously measure the output when corresponding LED are turned on. Pulse
oxymetry relies on photoplethysmographic changes in the arterial blood volume
synchronous with periodic contractions of the heart. Amplitude of the signal depends on
the amount of blood ejected from the heart in the peripheral vascular bed with each
cycle, the optical absorptions of the blood, the composition and color of the skin and
underlying tissues and the LEDs used to illuminate the blood. This method allows obtain
information about heart work and oxygenation of peripheral blood simultaneously.
Other types of biosensors
Many sorts of sensor have specific functions. For example, biosensors can have
some sort of recognition element like an enzyme, antibody or receptor which provides
the selectivity to the object of interest that researcher wants to detect or to measure.
The transducer converts the biochemical reaction energy into the form of an optical,
electrical or physical signal proportional to the presence of a certain chemical
characteristics.
Optical fibers
In optical biosensors can used part included optical fibers (for more details see
chapter “Elements of wave optics“). They allow to illuminate, to observe and to measure
optical characteristics of inner cavities of a body. At the same time other procedures can
be provided in studied cavities, for example, surgical operation. In one bunch with
optical fibers (illuminant and observation) other systems for distant influence and
measuring can be used, including different sensors.
Endoscopic methods
Endometry is diagnostic technique at which measuring are carried out far off,
outside of a field of vision in various cavities, for example, in a gastrointestinal tract,
blood vessels and cardiac cavities, in abdominal cavity. Thus manifold data units, for
example, рН (acidity), pressures, temperatures, optical and others are applied. In heart
cavities it is possible to measure pressure using electrical micromanometer (Ø 1–2 mm)
at the end of heart catheter.
Radioprobe (endoradiosonde) is used for examination of gastrointestinal tract. It
is similar to pill enclosed power source, sensors and microradiogenerator. After
swallowing on radioprobe goes by native path and sends signals to the receiver.
Pacemaker, pacing lead
Pacemaker (pacing lead, cardiomonitor) is device for control of heart work. It is
miniature generator of electrical pulses with frequency and form necessary to set heart
contraction disturbed as result of illness. It is implanted device. Now power supply can
be made through skin without skin damage by way electromagnetic induction link.
Modern pacemakers use built-in sensors, logical microcircuitries and change frequency
of stimulus under needs.
35
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.1. Basis of mathematical analysis, probability
theory and mathematical statistics. Biomechanics. – Poltava, 2008. –120 p. –
Chapter 4.
Additional textbook, journals and references:
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
─ Roland Glaser. Biophysics: An Introduction.– 2010.
36
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Electrodynamics. It medical use. Bases of medical
equipment.
Biophysical bases of rheography. Learning of work of a
rheograph.
1
medical, stomatological
Poltava – 2016
37
The topic significance:
Study of physical properties of biological tissues has the important meaning for
diagnostics and researches in medicine and biology. The important fact is that which
rheography not damages object, which is studied.
Specific targets:
To know electrical current effects on tissues;
To know and explain processes caused by electrical current in tissues;
To explain dependence of tissue impedance on electric properties of frequency;
To influence of blood supply changes on electrical current in tissues;
To understand, to remember and to use the knowledge received;
To be able to carry out rheographic studies.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing
To know concepts: direct and alternating electric current,
disciplines):
ohmic resistance, imaginary impedance (reactance),
physics, biology
impedance, conductance, gradient. Ohm’s law in case direct
and alternating current in chains conteined resistances and
conductances. Character of blood supply of tissues.
To describe them.
The
subsequent To know character of electric properties of tissues as a
disciplines:
result of blood supply peculiarities.
Normal
physiology, To explain from which elements consist electrical equivalent
cardiology
circuit of a bioiogical tissue.
To explain the main mechanism of direct current effect on
biological tissues.
To explain the main mechanism of alternating current effect
on biological tissues.
To explain the dependence of tissue impedance on
alternating current frequency.
To know meaning of rheography method.
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Impedance
Total electrical resistance of electric chain or object in case of
alternating current.
Electrical equivalent
Electrical circuit that has similar electrical characteristic like
circuit
object under investigation.
Rheogoniometry
Rheographic investigations
Threshold current
Minimal value of alternating or pulse current causes irritation in
excitable tissues.
Perception current
Threshold current in case of alternating current.
Unreleasing current
Alternating current, which cause muscle contraction that will
result in clenching the conductor with the bare hand.
Threshold of
Minimal current when a person cannot unclench the hand by
unreleasing current
himself and release current distributor.
Theoretical questions to class:
1. What are ohmic resistance, imaginary impedance (reactance), impedance?
2. Formula for resistance calculation at series connection of resistors? At series
connection of capacitors?
3. Formula for resistance calculation at parallel connection of resistors? At parallel
38
connection of capacitors?
4. Electrical characteristics of biological tissues.
5. Dependence of tissue impedance on alternating current frequency.
6. Electrical equivalent circuits of a biological tissue.
7. Direct current effect on biological tissues.
8. Alternating current effect on biological tissues.
9. Why impedance decrease at increase of electric field frequency?
10. Why impedance decrease at increase of blood vessel filling?
11. Rheography, it assignment, using in medicine, diagnostic meaning.
Contens of the topic.
A lot of diagnostic and therapeutic methods used in modern medicine are based
on effects occuring in human body tissues under the influence of electrical currents and
electromagnetic fields. These currents and fields action and accompanying Observed
phenomena depend on current characteristics and electrical characteristics of biological
tissues.
Electrical characteristics of biological tissues
Biological tissues conduct current. Ions are current carriers in tissues i.e. tissues
are ionic conductors (or second class conductors).
Electrical current effect on tissues depends on current type. The following
current types are distinguished: direct, pulse (effect depends on impulse shape) and
alternating ones.
Direct current effect on biological tissues
Direct current is flowing through tissues under influence of applied constant
voltage. A current strength (I) and a current density (J = I/S) are direct current
characteristics. Current strength (or current commonly) in tissues is determined by an
applied voltage (V) and tissue specific resistance (ρ) or specific conductance (σ = 1/ρ).
Specified resistance has name active (ohmic). I = V· σ.
Ions in tissues flow uninterruptedly: positive ions shift to one side and
accumulate in particular parts of tissues; negative ions shift to opposite side and
accumulate in opposite parts of tissues. The main mechanism of direct current effect
on biological tissues is change of ion concentrations in different parts of tissues in
comparison with usual concentration. This appearance has name polarization.
If voltage is constant then direct current flowing in tissue can significantly
decrease during any time to minimal value. It is result of that fact that when ions shift
and ion concentration changes in different parts of electric field exposed tissue, the
ions form an electric field in tissues. It name is electromotive force of polarization. This
field has direction opposite to external field. It compensates an external field partly and
reduces current.
Alternating current effect on biological tissues
Alternating current is characterized by voltage, current strength, frequency (and
quantities, referred to frequency – cycle frequency and period), and phase. Voltage
caused alternating current change by harmonic function (sinusoid). Pulse currents are
characterized by voltage, current strength, impulse shape, and frequency. If impulses
have one-side voltage change only, them typical effect is irritation.
Alternating current influence on live tissues has different effects in dependence
on current frequency. If frequencies are low, alternating current similar to pulse current
causes irritation of excitable tissues.
If frequencies are high, when charged particles shift is not great in tissues,
calorific effect takes place, i.e. there is a heat emission in tissues as a result of current
flowing.
39
In case of alternating currents, tissues current-conducting properties depend on
current frequency as tissues has apparent capacity properties. It means that impedance
(total resistance) is characteristic of tissue at alternating current.
Biological tissue impedance has an active (ohmic) component and a reactive
(capacity) component. Dependence of conducting properties in case tissue impedance
upon alternating current frequency is shown in fig. 1.
Fig.1. Typical tissue impedance dependence on alternating current frequency.
Biological tissues capacity properties are specific to cellular membranes. A
membrane has dielectric properties to a greater extent; it is located between two
conductors (cell contents and intercellular fluid), like a dielectric layer in a condenser.
Lightning is dielectric breakdown of air by voltage buildup has E=3·106 V/m, that
exceeds the dielectric strength of air. Typical rest voltage drop on biomembranes is
E=10·106 V/m.
Besides, there are tissues that conduct current very slightly, for example, a dry
skin. The skin covering the whole human body increases its capacity properties in
general.
An electrical circuit having impedance dependence on alternating current
frequency similar to shown in fig. 1 consists of resistors and capacitors. The simplest
circuit of such type is shown in fig. 2. This circuit is called an electrical equivalent of a
biological tissue. Here a resistor Re corresponds to extracellular fluid, a capacitor C
corresponds to cell membranes, and a resistor Ri, corresponds to intercellular contents.
But, grades on impedance–frequency diagram of this scheme will be absent.
Fig.2. Equivalent electrical scheme of a biological tissue.
Different processes, developing ia tissues (inflammation, necrosis etc.) change
these tissues electrical parameters. Hence, values and form of dependence of
impedance upon alternative current frequency change too (fig.3).
40
Fig. 3. Muscle tissue impedance dependence on alternating current frequency in
different states.
When alternating electric fields influence over biological tissues, alternating
electrical currents are generated in tissues. Ions, that are current carriers in tissues, are
relatively sluggish. Their displacements become not great during field period, ions
vibrate only but remain location, if frequency are very high. From the other side, when
frequencies are high, currents in dielectrics (non-conductors) play an important role.
These currents are charged particles forced oscillations (ions movement, polar
molecules orientation). Therefore, the electromagnetic field frequency increases, the
difference in nature of charged particles movement in conductors and dielectrics
decreases.
Alternating current like pulse current causes irritation in excitable tissues only if
current is equal to or greater than threshold current. Threshold current increases as
alternating current frequency increases (i.e. alternating current irritant action decreases
as frequency increases). In case of alternating current threshold current is also called
perception current.
A threshold of unreleasing current is minimal current, when a person cannot
unclench the hand by himself and release current distributor. It characterizes
alternating current irritant action on human body also. If one touches an alive (under
voltage) conductor with a bare hand, it can cause muscle contraction (spasms) that will
result in clenching the conductor with the hand.
Medical methods based on use of alternating curren. Rheography.
An alternating current of frequency 30 kHz is used in diagnosis for detection of level
of filling tissues with the blood. Currents, which strength is less then threshold current,
are used in this case, i.e. currents that do not irritate excitable tissues. , Diagnostic
method based on registration of changing of tissue impedance that takes place due to
change in tissues filling with the blood (that was caused hy heart functioning) is called
rheography (or impedance plethysmography, or rheoplethysmography).
Rheoencephalogram is result of brain examination with the help of rheography.
Arterial vessels of heart, lungs, liver and extremities can be examined with the help
rheography. In stomatology vessels of periodontium, mouth mucous tunic, salivary
giands etc. can be examined with the help of rheography.
Rheodentography (rheoodontography), a method that is similar to rheography, is
used in stomatology. Tooth pulp is examined with the help of rheodentography. An
alternating current of 0.5–1 MHz frequencies is used for this purpose.
41
Fig. 4. Example of rheoencephalogram. Upper curve is rheogram proper, middle curve
– differential rheogram, third curve – is cardiogram, and lower – simultaneous
phonocardiogram (sounds appeared at heart contraction). All these parameters
are recorded concurrently. Differential rheogram is technical method of obtaining
information similar to derivative of rheogram. It gives information about cusp,
maximum and minimum points.
Practice work executed at class:
Measurement of an impedance of alive tissues.
Rheograph 4-РГ-1.
Device is intended for scientific research of blood supply, pulse wqves, vascular
tone and so on. It can be used for clinical examination of patients.
Method of measurement is impedance pletysmography. Studied tissue part is
sonded by high-frequency current (120 kHz). Resistance changes are transformed to
electrical signal and must be registered by any registering device with correspondingly
connector.
Maximal current through the object is 2,5 mA. Calibration signal is corresponds to
0,2; 0,1; 0,05 or 0,02 Ohm.
This device has 4 channels for rheogram and 4 channels for differential
rheogram.
1.HF current
generator
2.Commutator
3.Amplifier
4.Differentiator
5.Recorder
Fig.5. Block scheme of the rheograph 4-РГ-1.
HF current generator generates high frequency oscillations. Commutator has
balance (bridge) scheme includes R patient and R balance. At patient resistance
change in measurement diagonal of bridge then voltage difference appears. There is a
possibility to calibrate scheme. Generator frequency is 120 kHz.
Differentiator is device for obtaining a first derivative of the rheogram.
Work order.
42
During work it is necessary to ground device accuracy, as it removes
interferences [disturbances, noises].
Rheograph Р4-02.
It is intended for biological objects impedance measurement in range from 10 to
250 Ω with error in ±10% limits.
Sonde current has rectangular shape impulses with amplitude 1,6–2,0 mA.
Sonde current frequencies are:
I canal – 40 kHz;
II canal – 50 kHz;
III canal – 70 kHz;
IV canal – 100 kHz.
Rheograph must be verilied one time in 6 monthes.
7. Measuring
device
1.HF current
generator
2. Explored
object
3. Input
device
5.Amplifier
6.Analoguedigital
converter
8.Differentiator
To the recorder
Fig.6. Block scheme of the rheograph Р4-02.
Switcher position of the measurement mode is (upper), of the calibrating mode is
▼ (lower).
Switcher is intended for mode choice: pulled (unpressed) position for
measurement mode, pushed (pressed) position for calibration mode.
Calibration is realised automatically by special control signal.
Switcher is intended for indication of corresponding choice (channel selection).
Simultaneous switching on two channels is forbidden.
Socket is intended for electrodes connection.
Socket is intended for commutation connection (output to registering device).
Clamp is intended for grounding connection.
Rheograph Р4-02 use order.
1. Switch on device: press button СЕТЬ. Wait 5 min for device heating.
2. Connect cables to the device input sockets. Uppress switchers of unselected
channels; press switcher of selected channel.
3. If laboratory work includes study of organism tissue impedance:
Patient have to sit or lay. It is necessary to clean sites for electrodes on patient skin
by alcohole; to dry them. To cover electrodes by electrode paste and to fix them on
studied body part.
4. If laboratory work includes study of equivalent circuit impedance: see below.
Task 1:
Measurement of an impedance of equivalent circuit.
Recommendations.
Connect cable to the device input socket.
– to press the button of the channel, which corresponds to the certain frequency on a
digital panel and to receive size of a base impedance;
– the measurement of a base impedance is necessary for making on some times on 4
frequencies:
43
40 kHz (1-st channel of rheograph); 50 kHz (2-nd channel of heograph); 70 kHz (3-d
channel of rheograph) and 100 kHz (4-th channel of rheograph);
– to calculate average arithmetic and to bring results in the table:
Table
N
Z,Om
40 kHz
50 kHz
70 kHz
100 kHz
1
2
3
Mean
Task 2:
Draw a graph an impedance – frequency dependence.
Recommendations.
Mark frequency values on horisontal axis, impedance – on vertical. Don’t forget
about uniform scale use!
Make the conclusion.
Self-control material:
Test tasks (α=ІІ)
1. Cytoplasm of cells and an intercellular (interstitial) fluid is..., cellular
membrane is …
А. dielectric; electrolyte
В. conductor; semiconductor
С. semiconductor; dielectric
D. electrolyte; dielectric
Е. conductor; dielectric
2. At rheographic measurings they use...
А. Impulse currents
В. Alternating currents of high frequency
С. Direct current
D. Sounding (probing) currents of small quantity
Е. Electromagnetic waves
3. Dependence of an impedance of a living tissue on frequency is caused
А. Frame of a field of a tissue
В. Presence of an intercellular fluid
С. Blood supplay of organs and tissues
D. Different mobility of ions
E. Dependence of electrical properties of a tissue on frequency
4. The analysis of a rheogram allows to determine:
А. Period of a cardial cycle
В. The sizes of vessels
С. An elastance of vessels
D. A cardiac work
Е. Tone of vessels
5. Electrochemical polarization arises...
А.. As a result of formation of local concentration spatial charges
В. Owing to the phenomenon of an electrolysis of solute
С. At passage of a high frequency current
D. At passage of a direct electric current
Е. Owing to eraction between a dissolvent and productions of an electrolysis
6. The dispersion of an electrical conductivity of a living tissue is...
А. Result of dependence of the fissile resistance from alternating-current frequency
В. Dependence of an electrical conductivity of a living tissue on alternating-current force
С. Result of dependence of a capacitive reactance from alternating-current frequency
44
D. Dependence of an impedance of a living tissue on alternating-current frequency
Е. Result of influence of polarization capacity (it is especially for low frequencies)
7. By results of rheographic measurings it is possible to determine:
А. Volume of vessels
В. Changes of volume of a blood
С. A stroke output of a blood
D. Diameter of vessels
Е. Volumetric rate of a blood-groove
The subject of the research work.
To prepare a report on the subject «Rheography in stomatology »; «Rheography in
general therapy».
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009. – 1–2 vol.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.2. Basis of thermodynamics. Biomembranes.
Electricity and magnetism. –Poltava, 2015. –120 p.
Additional textbook, journals and references:
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
─ Biophysics and medical informatics. – Marzeniuk V.P. et all.– Ternopil,
Ukrmedkniha, 2004.– 480 p.
─ Roland Glaser. Biophysics: An Introduction.– 2010.
─ Philip Nelson. Biological Physics (Updated Edition).– 2007.
─ Paul Davidovits. Physics in Biology and Medicine, Third Edition (Complementary
Science). – 2007.
С. An elastance of vessels
D. A cardiac work
Е. Tone of vessels
5. Electrochemical polarization arises...
А.. As a result of formation of local concentration spatial charges
В. Owing to the phenomenon of an electrolysis of solute
С. At passage of a high frequency current
D. At passage of a direct electric current
Е. Owing to eraction between a dissolvent and productions of an electrolysis
6. The dispersion of an electrical conductivity of a living tissue is...
А. Result of dependence of the fissile resistance from alternating-current frequency
В. Dependence of an electrical conductivity of a living tissue on alternating-current force
С. Result of dependence of a capacitive reactance from alternating-current frequency
D. Dependence of an impedance of a living tissue on alternating-current frequency
Е. Result of influence of polarization capacity (it is especially for low frequencies)
7. By results of rheographic measurings it is possible to determine:
А. Volume of vessels
В. Changes of volume of a blood
С. A stroke output of a blood
D. Diameter of vessels
Е. Volumetric rate of a blood-groove
The subject of the research work.
45
To prepare a report on the subject «Rheography in stomatology »; «Rheography in
general therapy».
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.2. Basis of thermodynamics. Biomembranes.
Electricity and magnetism. –Poltava, 2014.
Additional textbook, journals and references:
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
─ Roland Glaser. Biophysics: An Introduction.– 2010.
─ Philip Nelson. Biological Physics (Updated Edition).– 2007.
─ Paul Davidovits. Physics in Biology and Medicine, Third Edition (Complementary
Science). – 2007.
46
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Electrodynamics. It medical use. Bases of medical
equipment.
The mechanism of operation of external electrical and
magnetic fields onto bioobjects. Electrophoresis.
Determination of mobility of ions
1
medical, stomatological
Poltava – 2016
47
The topic significance:
Sensor (measuring converter, transducer, data unit, sensing element, monitor,
sensing unit, transmitter) is part of measurement device that directly communicate with
object of examination and transform measurand [measured quantity] into form easy-touse of researcher; generally it is electric signal which is passed, processed,
represented, measured or registered next.
Most often measurand is physical quantity (pressure, displacement, temperature,
voltage and so on). Further only sensors with electrical output signal [pickup signal] will
be considered.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Previous (providing
Obtainable skills
disciplines)
Physics
To define basic concepts of physical parameters: pressure,
sound intensity, resistance, conductivity, capacitance,
inductance, temperature, illuminance, optical spectrum and
them interrelations.
To know measurement units of physical quantities.
Materials for the before-class work self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Biomedical
Biosensors are sensors used for reception of information on functioning
sensor
alive organisms, their organs and systems.
Electrode
conductor of the special shape and construction with which help the
explored field of a body or an organ of an alive organism is connected in
an electric circuit of the measuring device
Sensibility
minimal change of measured parameter which can be steady detected
Dynamic
range of input quantities in which measurement is carried out without
range
significant errors
Accuracy
maximal difference between obtained and nominal output values
Response
minimal time range during that output value reach the level corresponding
time
to level of input parameter
Reproducibility difference between output signals on equal input influences in different
time moments must be absent
Requirements – reception of an steady informative signal (functionally reliable);
for biomedical – minimum of distortions of the useful signal;
sensors
– maximum noise immunity;
– convenience of use and arrangement;
– absence of the side influences on an organism (safety); construction of
the sensor contacting to a body (in vivo applications) must be nontoxic
and nonthrombogenic;
– opportunity of sterilization (for sensors of reusable use);
– low cost (for sensors of unitary use).
Theoretical questions to class:
1. Classifications of sensors (electrodes and transducers; in dependence on the
quantity to be measured; bio-controlled and energy; according to physical nature
48
of input signal).
2. Requirements for biomedical sensors.
3. Metrological characteristics of sensors.
4. Electrodes types.
5. Requirements to electrodes of medical and biologic purposes.
6. Electrodes classification.
7. Mechanical measurement sensors.
8. Magnetic measurement sensors.
9. Temperature measurement sensors.
10.
Optical Biosensors.
11.
Piezoelectric transducers.
Content of the topic.
Sensor (measuring converter, transducer, data unit, sensing element,
monitor, sensing unit, transmitter) is part of measurement device that directly
communicate with object of examination and transform measurand [measured quantity]
into form easy-to-use of researcher; generally it is electric signal which is passed,
processed, represented, measured or registered next.
Most often measurand is physical quantity (pressure, displacement, temperature,
voltage and so on). Further only sensors with electrical output signal [pickup signal] will
be considered.
Biosensors (biomedical sensors, biomedical transducers) are sensors used
for reception of information on functioning alive organisms, their organs and systems.
All measured biomedical parameters can be divided into two groups: directly
measured and mediately measured. Mediately measured parameters are that can’t be
measured or that can be measured hardly or with the risk to healthy or uncomfortable. If
they influence on other parameters more comfortable for measuring, and these other
parameters are measured, we tell about mediately measuring.
Examples of directly measured parameters are motions of extremities and chest,
body temperature, biopotentials, body pressure in blood vessel. Examples of mediately
measured parameters are blood pressure (by sounds in time of blood flow), oxygenation
of hemoglobin by spectral characteristics of blood by light transmission of tissues and
further.
Sensors designed for medicine (biosensors) use must to meet the next
requirements:
–
reception of an steady informative signal (functionally reliable);
–
minimum of distortions of the useful signal;
–
maximum noise immunity;
–
convenience of use and arrangement;
–
absence of the side influences on an organism (safety); construction of the
sensor contacting to a body (in vivo applications) must be nontoxic and
nonthrombogenic;
–
opportunity of sterilization (for sensors of reusable use);
–
low cost (for sensors of unitary use).
Additional issues are the long term biocompatibility of the sensor.
Output electrical signal of sensor can be: current, voltage, impedance, frequency
of phase of alternating current or pulse signals.
Classifications of sensors
1). Biomedical sensors are divided on two groups: electrodes and proper sensors
(transducers).
Biomedical sensors are classified in dependence on the quantity to be measured:
– electrical;
49
– mechanical (linear and angular displacement, pressure, velocity, acceleration,
frequency of oscillations,…);
– physical (temperature, illuminance, sound intensity, humidity,…);
– physiological (filling of tissue by blood);
– chemical (concentration of certain ions, activity of ions,…).
2). Biomedical sensors can be bio-controlled and energy.
Bio-controlled sensors can be generator (active) or parametric (passive).
Parametric sensors change own electrical parameters (resistance, capacitance
or inductance) under the influence of measured object.
Generator sensors directly transform energy of input signal into electrical output
signal that is they generate corresponding signal. Some types of such sensors are: a)
piezosensors or piezoelectric transducers, b) thermoelectric transducers, c) induction
sensors used electromagnetic induction, d) photoelectric sensors.
Energy sensors are complex: firstly, part that influence of the organs and tissues
and, secondly, proper sensor. Energy flux of influence has strict characteristics;
measured parameter changes these characteristics, modulate them. Examples of such
equipments are ultrasound and photoelectrical sensors.
Metrological performances of sensors:
1) sensibility (sensitivity resolution) – minimal change of measured parameter
which can be steady detected; it shown as z = Δy/Δx, where Δy – change of output
signal at change of input value Δx, and measured thereafter in Ω/mm (Ohm per
millimeter) or mV/K (millivolt per Kelvin) and the like;
2) dynamic range (operating range) – range of input quantities in which
measurement is carried out without significant errors;
3) accuracy – maximal difference between obtained and nominal output values;
4) response time (response speed) – minimal time range during that output
value reach the level corresponding to level of input parameter;
5) reproducibility – difference between output signals on equal input influences
in different time moments must be absent.
Next terms are used often:
transducer gage – measuring device with converter;
transducer-converter – sensor- converter;
transducing apparatus – converter, device for converting.
Artefact - process or the formation not peculiar to an object of interest and
incipient during examination. They distort obtained information and often are result of
mistakes at matching or fulfilling of investigation method or sensors. For example, when
substance of sensor interacts chemically with investigated object. Struggle against
undesirable influences and artefacts is important and obligatory side of investigations.
According to physical nature of input signal sensors are divided on: mechanical,
acoustical (sound), optical and so on.
Electrical measurement
(include biopotential measurements)
Electrodes are conductors of the special shape and construction with which help
the explored field of a body or an organ of an alive organism is connected in an electric
circuit of the measuring device. More often they use at electrocardiographies (ECG),
electroencephalography (EEG), electromyography (EMG), electro-oculography, electrogastrography (EGG), rheography (REG).
Electrodes use also for electrical action on an organism from the outside, for
example, at medicinal electrophoresis, at rheography, at physiotherapeutic treatment by
pulsing currents, at using the device "electrodream".
Separately it is necessary to view the microelectrodes used for pickup of
electrical signals or electrical action at a level of separate cells and cellular ensembles.
50
Requirements to electrodes of medical and biologic purpose:
– are promptly fixed and removed;
– high stability of electrical parameters, absence of artefacts and noises;
– low losses of an electrical signal, including small transition resistance in zone of
contact to object;
– mechanical strength;
– absence of irritant action;
– low price.
Particularly strict requirements are made to implanted electrode, which must work
long time (many years in case of heart control).
When a metal is placed in an electrolyte (ionizable solution), an uneven charge
distribution is created at the metal/electrolyte interface. The charge distribution causes
an electric potential across the interface between the metal and the electrolyte. In more
details these processes are described in the chapter "Electrokinetic phenomena". As
result of these processes chemical change of the material of electrodes and studied
object, irritation of tissue, errors of measured signals can be observed.
Hydrogen is the standard half-cell potential. Stronger oxidizing agent have more
potential (F2>Cl2>Ag>Cu>H2), weaker oxidizing agent have less potential
(Li<Mg<Zn<Pb<H). For example, standard reduction potential at 25ºC for H equal to
0 V, for Ag 0,8 V, for Zn –0,76 V. It’s mean that if used two electrodes – Ag and Zn – in
one vessel with electrolyte, electric potential arises between them equal to 1,56 V.
The transient resistance "electrode - skin" can achieve hundreds kiloohms at a
dry clean skin. It depends on properties of a skin, such as metal of which the electrode
is made, contacting areas and a conducting medium between a skin and an electrode.
For diminution of the transient resistance the napkins imbued by a normal (physiologic)
saline solution, or more effective special conductive electrode pastes (electroding ink)
are used.
The major contacting area provides diminution of resistance, however gives in
distortions of a registered signal.
To manufacturing electrodes apply gold, platinum, iridium, tungsten, argentum,
palladium, stainless steel of a special composition, alloys with iridium, etc. Frequently
use the argentum electrodes coated by very thin layer of chloride argentums (Ag/AgCl
electrodes). The exact selection of metal and structure of the surface stratum of an
electrode, use of special electrode pastes allows to lower transient resistance and
effects of polarization too.
Tungsten is the most versatile and widely used probe material because of ifs
stiffness, biocompatibility and cost. It is ideal for most recording and electro-stimulation
purposes.
Platinum/iridium are extremely inert and is much more resistant to corrosion than
either tungsten or stainless steel when used in long time stimulation examinations.
Stainless steel is widely used due to its stiffness and it can be easily
electrochemically coated with other metals used in certain type of studies.
Pure iridium has by far the lowest concomitant tip impedance of any of the noble
metals. It is extremely inert and very resistant to corrosion.
Construction and performances of electrodes depend on the purposes of
application. To destination electrodes part on 4 groups:
1) For disposable application (for the functional diagnostics).
2) For the long-lived continuous observation (reanimation, intensive therapy).
3) For dynamic application (sports medicine, the check of a patient state in time of
sports rehabilitation).
4) For emergency application.
Main shapes of electrodes:
51
1) electrode plate;
2) vacuum cup (sucker);
3) olive at the ending of rubber or plastic catheter (used for esophageal
registration of ECG);
4) piercing (needle-type, acicular, trocar) electrode;
5) multipoint electrode;
6) capacitive pickup electrode;
7) snare (electrode with loop shape – active electrode).
Microelectrodes
Biopotential electrodes with an ultra-fine tapered tip are used that can be inserted
into individual biological cells. Commonly used in neurophysiology studies.
The tip of these electrodes must be small with respect to the dimension of the
biological cell wall.
Kinds of microelectrodes:
1) glass micropipette;
2) metal microelectrode;
3) solid-state microprobes.
Intra-operative electrod microelectrodes es can be available in Tungsten and
Platinum/Iridium core conductors covered by polymer insulator. Length of free tip can be
equal from 5 mm (electrodes for work with neuronal pools) to 5 μm (electrodes for work
with separate cells), thickness of covered layer can reach 1 μm.
Mechanical measurement
Sensors which are used for measuring of displacement (stretching or contraction)
term as strain gages (strain indicator, strain sensor). Devices used strain gages term as
tensometers (extensometer, strainometer). These names are used for pressure sensors
too, since object of measuring in both cases the same: displacement of sensor parts.
Displacement transducers (position transducer)
Potentiometer transduces linear or angular displacement into a voltage. When a
moving contact of variable resistor move, resistance between it terminals change; taked
off voltage changes correspondingly.
Elastic resistive transducers
l
R
S , where ρ – resistivity constant
Resistance of electric conductor equal:
(specific resistance) of material, l – length of resistor, S – cross-section area of resistor.
If resistor is elastic (can stretch and restore after removing of stretching force),
during the elongation cross-section area decrease.
Such sensor used for measuring of amplitude and frequency of respiratory
movements and for plethysmography (research of blood supply changing).
For example, elastic transducer is wrapped around the chest. The chest diameter
during exhalation is 33 cm; corresponding circumference is near 104 cm. During
inspiration volume and circumference increase, length of transducer increase, and its
resistance increase too.
Strain gauges
Gauge insensitive to lateral forces
It’s used in blood pressure transducers. Change in resistance is quite small.
Inductive displacement transducers (variable-reductance transducer)
Inductive displacement transducer or LVDT sensor (linear variable displacement
transducer, linear voltage differential transformer).
When the core moves towards one coil the voltage induced in that coil increases
proportionally.
52
n2 S
, where n – coil turns, μ – relative magnetic
l
permeability of the core material, μ0 – absolute magnetic permeability of vacuum, l –
solenoid length, S – cross-section area of solenoid.
Semiconductor strain gages are used for measuring of pressure.
Capacitors and capacitive transducers
The most common method to measure displacement is to change the plate
separation distance d.
This arrangement can be used to measure force, pressure or acceleration.
S
The capacitor capacitance is equal: C   0 , where S – the area of a plate
d
(armature) of the condenser; d – distance between plates; ε – an inductivity of medium
between plates; ε0 – absolute inductivity of vacuum.
If the distance between plates varies, the capacity varies inversely.
They are used to measure respiration or movement studies (when placed on a
mat). Capacitance sensors can measure ranges up to 300 nm with 0,1 nm resolution.
Piezoelectric transducers
Piezoelectricity – is originating of electrical charges displacement at strain of a
crystal (direct piezoelectric effect). If the crystal is mechanically strained, it generates a
small potential.
Inverse piezoelectric effect is a strain of a crystal under activity electric field in
case an electric field is applied across its plates.
Crystal contracts in direction perpendicular to direction of applied electric field and
turn, direction of originated electric field is perpendicular to direction of compression.
Piezoelectric sensors are active bio-controlled sensors.
Piezoelectric properties are observed at some kinds of monocrystal (native or
artificial), for example, quartz, and at artificial materials as piezoceramics and
piezopolymers. On the figure flexible polymer sensor is observed.
Piezoelectric sensor of simplest type is piezoelectric plate squeezed between two
metal facings.
Used widely in different – all – branches of science and techniques.
They are used in cardiology to listen to heart sounds (phonocardiography), to
automated measure of blood pressure, physiological forces and acceleration
measurements. Also they are employed as sources of sound and supersonic signals.
High frequency-sound waves greater than 20 KHz due to inverse piezoelectric effect.
Modern microphones used for studying of heard sounds are piezoelectric.
Sometimes used electrodynamic microphones in which inductance coil bound with
elastic membrane moved in static magnetic field under the influence of variable electric
current through coil that originates variable magnetic field in coil.
Using magnetic fields
Blood flow through an exposed vessel can be measured by means of an
electromagnetic flow transducer.
The probe contains coils that produce an electromagnetic field transverse to the
direction of blood flow.
The electric charges in blood (the anions and the cations) experience force
induced by the presence of the magnetic field. F = qvB, where F – induced force, q –
charge of particle, v – velocity of charge, B – inductance of magnetic field.
Charge of electron q = –1,602•10–19 C; it is equal to absolute value of positive
monovalent ion as Na+ or K+.
Oppositely charged particles move in opposite directions this movement causes
an opposing force: Fop = qE = qV/d, where V – voltage formed consequently, d –
diameter of vessel.
Inductance of solenoid L   0
53
At equilibrium qV/d = qvB => V/d = vB, therefore v = V/dB. Here V – measured
value.
Temperature measurement
It is the most often controlled physiological values and one of the four basic vital
signs.
Distinguish temperature of nucleus (core) of a body and temperature of body
surfaces – skin.
Inner (core) temperature is remarkably constant (37±0,5ºС). Temperature of the
skin changes in more wide limits. If slightly dressed person is in room with normal
conditions – 20ºС, temperature is equal to 36,6ºС in armpit, rectal temperature – 37ºС,
and lower at other skin areas (in the center of footstep 27–28°C), particularly on open
sites of extremities. Temperature is measured routinely in contact with the skin or inside
a body cavity. At measuring the surface temperature it is important to estimate
symmetry of temperature allocation that corresponds to norm and reflects intensity of a
blood supply of a body fields, and also presence possible inflammatory or neoplastic
processes. Temperature of a skin influence also a state of a surrounding medium
(temperature, air humidity), tone of vegetative nervous system, a body hair
development, clothes.
Temperature sensors are:
–
wire-wound termoresistors;
–
semiconductor-resistance thermometers;
–
difference thermoelements.
Thermistors (termoresistors ) – require direct contact with skin or mucosal
tissues. They can be made of compressed, sintered metal oxides (Ni, Mg, Co) or
semiconductors that change their resistance with temperature. Sensitive element of
device is small to produce a rapid response. Shapes of sensor are difference from
needle to flat.
Non contact thermometers used for determination of body core temperature inside
the auditory canal as temperature of temperature of ear canal near the tympanic
membrane is known to track the core temperature.
Noncontact thermometer
Temperature of the ear canal near the tympanic membrane is known to track the
core temperature very accurately – by 0,5–1ºC. Infrared radiation from the membrane is
channeled to a thermopile detector through a metal waveguide. Thermopile converts
heat flow into current.
Next step of distant thermometry are thermovision or thermography. Sensors
convert the infrared radiation into electrical signals. For more details see chapter
“Thermal radiation”.
Optical Biosensors
Usually as optical sensor are used photoresistors (for more details see chapter
“Interaction between light and tissue“), which change resistance under the influence of
incident light.
Arterial blood gases
Blood changes its color depending on the amount of oxygen bound to the
hemoglobin in the erythrocytes. Oxygenated arterial blood is light red; vein blood is dark
red with shifted spectral maximum of optical transmission.
Normal physiological conditions 98% of the total amount of oxygen is contained in
the erythrocytes in a loose combination of hemoglobin Hb and oxyhemoglobin Hb02.
The remaining 2% of oxygen is dissolved in the blood plasma. Oxygen saturation (SO2)
is the relative amount of oxygen carried by the hemoglobin in the erythrocytes. During
oximetry SO2 is determined.
54
Oximetry is based on the light absorption properties of blood and on the relative
concentration of hemoglobin (dark-red) and oxyhemoglobin (red).
Measurement is based on Beer-Lambert's law that relates absorption of light to
the properties of the material through which the light is transmiting.
Electronic circuits turn on and off sequentially the LEDs (light-emitting diodes) and
synchronously measure the output when corresponding LED are turned on. Pulse
oxymetry relies on photoplethysmographic changes in the arterial blood volume
synchronous with periodic contractions of the heart. Amplitude of the signal depends on
the amount of blood ejected from the heart in the peripheral vascular bed with each
cycle, the optical absorptions of the blood, the composition and color of the skin and
underlying tissues and the LEDs used to illuminate the blood. This method allows obtain
information about heart work and oxygenation of peripheral blood simultaneously.
Other types of biosensors
Many sorts of sensor have specific functions. For example, biosensors can have
some sort of recognition element like an enzyme, antibody or receptor which provides
the selectivity to the object of interest that researcher wants to detect or to measure.
The transducer converts the biochemical reaction energy into the form of an optical,
electrical or physical signal proportional to the presence of a certain chemical
characteristics.
Optical fibers
In optical biosensors can used part included optical fibers (for more details see
chapter “Elements of wave optics“). They allow to illuminate, to observe and to measure
optical characteristics of inner cavities of a body. At the same time other procedures can
be provided in studied cavities, for example, surgical operation. In one bunch with
optical fibers (illuminant and observation) other systems for distant influence and
measuring can be used, including different sensors.
Endoscopic methods
Endometry is diagnostic technique at which measuring are carried out far off,
outside of a field of vision in various cavities, for example, in a gastrointestinal tract,
blood vessels and cardiac cavities, in abdominal cavity. Thus manifold data units, for
example, рН (acidity), pressures, temperatures, optical and others are applied. In heart
cavities it is possible to measure pressure using electrical micromanometer (Ø 1–2 mm)
at the end of heart catheter.
Radioprobe (endoradiosonde) is used for examination of gastrointestinal tract. It
is similar to pill enclosed power source, sensors and microradiogenerator. After
swallowing on radioprobe goes by native path and sends signals to the receiver.
Pacemaker, pacing lead
Pacemaker (pacing lead, cardiomonitor) is device for control of heart work. It is
miniature generator of electrical pulses with frequency and form necessary to set heart
contraction disturbed as result of illness. It is implanted device. Now power supply can
be made through skin without skin damage by way electromagnetic induction link.
Modern pacemakers use built-in sensors, logical microcircuitries and change frequency
of stimulus under needs.
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009..
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. –Poltava,
2008. –120 p. –Chapter 4.
Additional textbook and journals:
55
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
56
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 6
Topic
Year
Faculty
Medical and biological physics
Bases of medical physics
Electrodynamics. It medical use. Bases of medical
equipment.
Fundamentals of the UHF-therapy and the UHFinductothermy.
1
medical, stomatological
Poltava – 2016
57
The topic significance: the is very important for future doctors in their professional
activity, positively influences the students in their attitude to the future profession, forms
professional skills and experience as well as taking as a principle the knowledge of the
subject leamt.
Specific targets:
─ To mastering with principle of operation of UHF-therapy device and UHFinductothermy device;
─ To know principles of effect of UHF electic and magnetic fields on bologic tissues
and organisms;
─ To be able to carry out laboratory and experimental work with UHF-therapy and
UHF-inductothermy devices;
─ To research process of UHF electic field energy absorption in electrolites and in
dielectrics;
─ To form the professional experience by reviewing, training and authorizing it.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects
Disciplines
Obtainable skills
Previous (providing
To know bases of electrodynamics.
disciplines):
To know mechanism of electrolytic dissociation,
physics, chemistry, biology appearance of ions, radicals, peroxides, hydroperoxides.
To describe mechanism of formation of diffusion potential
(electrochemical potential).
To describe electrokinetic appearances.
To know structure of oscillatory circuit (oscillating loop),
Thomson formula.
To describe appearance of relaxation oscillations and
continuous (persistant) oscillation.
To explain the essence of the methods: UHF-therapy,
SHF- therapy, inductothermy.
To write down and analyse the formula for quantity of heat,
allocated in a unit volume for a time unit at the influence of
UHF electric field.
To explain principle of operation of UHF-therapy device.
The
subsequent To know effects of alternating electric fields on cells,
disciplines:
tissues and whole organism functioning.
Normal physiology
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
UHF
Ultra-high frequencies 30–300 MHz
SHF-radiation
Superhigh frequency electromagnetic radiation 300 MHz–30
GHz
SHF-therapy
Superhigh frequency therapy
Microwave radiation
Electromagnetic wave of frequencies more than 300 MHz
Radio-frequency
Oscillations with frequencies 200 kHz–30 MHz
oscillations
Inductothermy
Influence on bioobject by alternating magnetic field
Theoretical questions to class:
1. What are electric field (EF), magnetic field (MF), electromagnetic field (EMF)?
2. Describe basic characteristics of these fields. Note formulas and measurement units
of EF, MF, and EMF basic characteristics.
58
3. Describe mechanism of action of EF, MF, and EMF on biological tissues in
dependence on fields characteristics.
4. What is polarization?
5. What is case of electric currents?
6. Why field energy is absorbed in mediums?
7. Describe mechanism of biologic tissues heating in UHF electric and magnetic fields.
8. Essence of the method of UHF-therapy.
9. The mechanism of influence of UHF electric field on human tissues.
10.
Essence of the method of inductothermy.
11.
Function of units of the apparatus for UHF-therapy.
Practice work executed at class:
To study:
─ manual of UHF-therapy device and UHF-inductothermy device;
─ block diagrams of these devices.
To do:
─ research of heating of dielectric (nonconductor) and electrolyte in fields of UHFtherapy and UHF-inductothermy devices.
─ draw up protocol.
Investigate dependence of temperature of an electrolyte and an nonconductor on the
time of UHF electric field influence on it.
Fig.1. The block scheme of UHF-therapy device УВЧ-66.
1. Learn the block scheme of UHF-therapy device. Draw it.
Read manual of device.
2. To prepare UHF-therapy device for work:
─ connect device to power grid;
─ switch on device, to let it to heat 3–5 min.;
─ set power 40 W;
─ neon lamp allocated between plates of therapeutic contour must shine of bright rosecolored light;
─ set cuvettes with electrolyte (NaCl solution) and with dielectric (turpentine oil) in
therapeutic contour;
─ to tune UHF-therapy device in resonance.
3. To carry out study of electrolyte and dielectric heating in UHF electromagnetic field: to
write down temperature data each 5 min. into the table.
4. To draw graph of temperature (Cº) on time (min.).
5. To draw conclusion.
Table.
Time, min
Temperature
Electrolyte
Nonconductor
0
59
5
10
15
20
25
─
Contens of the topic.
Abbreviations:
EF – electric field;
MF – magnetic field;
EMF – electromagnetic field;
BT – biological tissue, biological cell.
Electrical currents can be induced in tissues without electrodes, if tissues (some
parts of huruan body) are placed into an alternating electromagnetic field, alternating
currents are induced in them. Heating of tissues with the help of currents induced by an
alternating field is the base of the following methods, such as inductothermy, UHFtherapy (UHF – ultra-high frequencies), and microwave therapy (SHF-therapy).
An important point is that effect of high-frequency electromagnetic oscillations on
the human body is not only thermal.
Electrical current effect on tissues depends on current type. The following
current types are distinguished: direct, impulse (effect depends on impulse shape) and
alternating ones.
Fig.1. Impulse currents graphs at different impulse shapes.
The impact of radiation on human body is present even then when thermal effect is
insignificant. The action of electromagnetic radiation on human body is not studied
enough. It is apparent that biological action of radiation can be seen on different layers:
subcellular (molecular), cellular, on tissue level, organs, body, population, and global
one.
The result of unfavorable effect of electromagnetic radiation of radio frequency range
can be both direct pathological phenomena (internal diseases or dysfunction) and
weakening of human body protection and adoption. It is accepted as correct a negative
effect of high intensity electromagnetic radiation on cardiovascular, central nervous,
endocrine, hematogenic and other systems. Alternating electro magnetic fields effect
can cause dizziness, high fatigability, high irritability, memory weakening, insomnia,
general weakness and other negative results. If even small electromagnetic fields act
upon human body for a long time, they cause strong dysfunction in cerebral cortex.
Strict hygienic standards of permissible levels of electromagnetic fields acted upon
human bodies are developed in this connection. Within the frequency range from 30
kHz to 300 MHz electric field intensity (E) (characteristic of electrical component of
60
electromagnetic field) is standardized. Within the frequency range from 300 MHz to 30
GHz electromagnetic radiation energy flux (i.e. energy of electromagnetic radiation
acted upon unit of surface area during unit of time) is standardized.
Biological tissues have resistance and capacitive properties.
Medical methods based on use of alternating electromagnetic field.
Inductothermy. During inductothermy an alternating magnetic field effects
patient's tissues. A standard instrument for inductothermy produces magnetic field
changing with a frequency of 13,56 MHz or 40,68 MHz. A magnetic field is produced
with the help of coil (an inductor) through which an alternating electrical current of a
corresponding frequency flows.
An alternating magnetic field induces eddy currents in tissues, when those
currents flow tissues are heated and heat is evolved.
During inductothermy a specific heat power evolved in unit of the volume is
defined by the formula:
Q = ν2σH2, where ν is frequency of alternating magnetic field, σ – electric
conductance of tissue, H – magnetic field strength.
Or Q = kω2B02 / ρ, where k is proportionality factor, dependent on the sample
geometry; ω – cyclic frequency of alternating magnetic field; B0 – amplitude of magnetic
induction, ρ – specific conductivity.
Hence, tissues having less specific resistance (good conductors) are heated
better.
The tissues are heated effectively upon the depth of 6–8 cm. An increase of
temperature in tissues intensifies the circulation of the blood in them, causes different
ferments activation. In the course of inductothermy human body immune system is
being stimulated.
UHF-therapy. In the course of UHF-therapy an alternating electric field of UHFrange (frequencies of 30–300 MHz) effects on a patient's tissues.
A standard instrument for UHF-therapy induces electromagnetic oscillations of
460 MHz frequency (the wavelength is about 65,2 cm – decimeter range) or 2375 MHz.
The UHF-field induces electric currents in a patient's tissues (more precisely,
charged particles oscillations – bias currents) of the same frequency as the frequency of
the UHF-field. Emerged currents heat patient's tissues, moreover when these
frequencies of electromagnetic radiation are used, the hottest are those tissues, which
have less conductivity, i e. tissues-dielectrics.
At frequencies 40,68 MHz dielectrics are heated more than electrolites also.
A specific heat power, evolved during UHF-therapy, is defined by the formulas:
In electrolytes:
q1 = E2/, where E – electromotive intensity (electric-field intensity),  – specific
resistance of electrolyte.
In dielectrics:
2
q2 = ω E εε0tgδ, where ω – cyclic frequency of alternating magnetic field, εε0 – dielectric
permittivity of medium, δ – angle of dielectric loss, E is a root-mean-square value of electricfield intensity. Or q2 = ω E02εε0tgδ / 2.
E = Ea / √2, where Ea is the amplitude of electric-field intensity (effective electric
field strength).
SHF-therapy (superhigh frequency therapy). If SHF-therapy is used for healing
patient's tissues, it means that patient's tissues are affected by electromagnetic waves
with frequency within the range of 300 MHz–30 GHz. At SHF-therapy the muscle
tissues and the blood are heated well, as they take up radiowaves well, as absorption is
caused water content mainly. Fat and bones are heated less.
61
The commonly used devices are those ones that ptoduce electromagnetic waves
from the following standard wavelength values: for decimetric waves (DMW) therapy
(λ = 65,2 cm, ν = 460 MHz), for microwave (MW) therapy (λ = 12,6 cm, ν = 2375 MHz).
Decimetric waves and microwave therapies differ from each other in the depth of
radiation penetration in tissues. When decimetric therapy is used,
The depth of decimetric waves penetration in tissues is near 9 cm; the
microwave penetration depth is near 3–5 cm.
Direct electric and magnetic fields.
Direct electric field influence on tissues causes dielectric polarization due to
molecules reorientation: which behave as dipoles. It results in ions shift and change of
their concentration in different areas of tissues. Ions shift lasts until electric field that
they have developed wilt not compensate external electric field effect on ions.
Electrostatic shower (or franclinization) and aeroionic therapy. At that a patient is
placed in a strong electrostatic field (voltage up to 50 kV is used), where partial air
ionization occurs. As this takes place, aeroions are produced as well as air ionization
products – ozone and ozone oxides that irritate skin receptors and mucous membrane
receptors of respiratory tract.
It activates functional state of central nervous system, raises neurologic level,
improves sleep etc.
Magnetic therapy – direct and low frequency alternating magnetic fields biological
effects on human body are not studied enough. Weak heating effect, stimulation of
regeneration, influence on chemical reactions behavior take place in magnetic fields.
Other ELECTROPHYSIOTHERAPY
Galvanizing is application with the medical purpose of a continuous constant
electric current of small force (up to 50 mА) and low voltage (30-80 V). The mechanism
of activity: enriching of microcirculation; rising of vascular walls permeability;
metabolism rising; englobement activation; distracting, anesthetizing activity due to
irritation of skin receptors.
Faradization is application low frequency alternating-current with the medical
purpose. The mechanism of activity: drop of nervous cells excitability - decrease of
pains as a result; rising of nervous tissue metabolism;
Darsonvalization is application with the medical purpose alternating-current high
frequency, high intensity and small force. The mechanism of activity: local depressing of
dermal sensitivity reaching at sufficient duration and intensity of a current almost up to
the complete anaesthesia; narrowing, and then the dilating of dermal vessels promoting
enriching blood circulation and lymphokinesia, nutrition of tissues, to augmentation of
metabolic product outflow.
Franklinization is application of static electricity for the medical purposes. The
mechanism of activity: it is insufficiently investigated: there are discordant data on
influence on arterial pressure, body temperature and metabolism.
Diadynamic [currents] therapy is treatment by two low-frequency impulse
currents of small force (up to 50 mА). The mechanism of activity: analgesic activity; a
stimulation of metabolic processes; a stimulation of an englobement.
Fluctuorization (Флуктуоризация) is application with the medical purpose
variable, in part or completely a rectified current of low voltage (up to 100 V) with
chaotically changed (up to 2000 Hz) frequency and amplitude (up to 3 mA/sm2).The
mechanism of activity: least excitant activity is rendered with the symmetric oscillations
of a current as changes of ion density at semipermeable membranes in some degrees
are flattened by the same changes of ion density occuring in opposite direction at
current veering (sense of current). Aperiodicity of change of peaks originating of
exaltation rises stimulating activity and reduces tissues adaptation in comparison with
62
activity of periodic oscillations of current with identical voltage. More strong activity
rectified oscillations render in part have, even more strong - completely rectified.
Electropuncture (Электропунктура) method of action on biologically active
points (sites) of an organism certain currents types of low and high frequency (use
impulse currents of low frequency more often). The mechanism of activity: analgesic
activity; hyposensitive activity; mobilization of nonspecific protection mechanisms of an
organism due to its adaptable responses.
Electrodream action by impulse currents of small intensity with the purpose of
normalization of a function state of central nervous system through the receptor
apparatus of a head. The name of a method appeared unsuccessful. During wide
application of it was found out, that medical activity of it is not always connected to
dream.
Inductothermy. The method of the electrotreatment, working factor of which is a
high-frequency variable magnetic field. Activity of energy of this field produces
appearance of the induced (inductive) eddy (vortex) currents which mechanical energy
transfers in heat. Vessels extend, the blood-groove is accelerated, arterial pressure
drops, and the coronary circulation is enriched. Anti-inflammatory and resorptional
activity of inductothermy is connected to thermogenesis and intensifying of a bloodgroove. There is also a depressing of muscles tone that matters at spastic stricture of a
smooth musculation. Depressing of excitability of nervous receptors causes
anesthetizing and sedative activity.
At this method of treatment it observes rising calcium content in tissues,
bacteriostatic activity. Indications to inductothermy administration are subacute and
chronic inflammatory diseases of internals organs of a small pelvis, ENT (ear, nose,
throat) organs, diseases and traumas of a locomotorium, peripheric and central nervous
system.
Electrical stimulation is application of an electric current with the purpose of
activation or intensifying of activity of fixed organs and systems. The words "electrical
stimulation" is frequently used completely improperly for notation of any action by an
electric current. To stimulate by currents it is possible many organs and systems; for
this purpose it is necessary application adequate procedures and parameters.
In practical work the widest application have received electrical stimulation of
heart that is special partition of medicine, and electrical stimulation of motor nerves and
muscles.
Electrical defibrillation is carried out with the help of a single current impulse of
sufficient force and duration, generated in the special device - a defibrillator.
Implantable heart pacemaker. Device that supply normal heart rhythm at
deseases harming own heart pacemaker – sinoatrial node.
Electrical stimulation of muscles. It is applied with the purpose of a stimulation
of regeneration of the muscle apparatus after traumas and the long-lived
immobilization.
Self-control tests.
1) Indicate correct formula for calculation of evolved heat quontity at dielectric heating:
1.q  k W   wE 2 tg
3.q  E 2
A) q = ω E02εε0tgδ / 2; B) q = kω2B02 / ρ; C) q = ν2σH2; D) q = E2/.
2.q  kB 2 2
4.q  k 0 2 E 2 tg
2) Indicate correct formula for calculation of evolved heat quontity at electrolite heating:
63
2.q  kH 2
1.q  kw 2 E 2
A) q = ω E02εε0tgδ / 2; B) q = kω2B02 / ρ; C) q = ν2σH2; D) q = E2/.
H2
3.q  k L
1.T  2 
C
4.q  kC0W 2 H 2 tg
5.T  2LC
2.T  2
L
3) Indicate Tomson formula: 1. 
1
2 LC
2. ω 
4) Indicate formula of natural frequency:
1

L
1. 
2. ω 
3. ω 
LC
C
2 LC
3.T  2 LC
4.T 
4. 

L
3. ω 
LC
C
4. 
C
L
C
L
1
2 LC
5) Treatment with inductive currents was prescribed for the patient. Indicate tissues, which
are heated more:
A) blood, lymph, skin;
B) blood, lymph, muscles;
C) skin, muscles;
D) bones, skin.
6) Conduction currents heat more effective follows tissues:
A) blood, skin, muscles;
B) bones, skin;
C) bones, skin, muscles;
D) skin, blood, lymph, muscles.
Task 1.
To calculate capacitance of human body with 70 kg mass. To set: this capacitance is equal
the capacitance of the sphere with mass equal to the human mass. Average density of the
human body is equal to 1 g/cm3.
The subject of the research work.
To prepare a report on the subject «UHF-therapy in stomatology and general therapy».
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. –Vol.2. Basis of thermodynamics. Biomembranes.
Electricity and magnetism. – Poltava, 2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
64
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 7
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Optical methods. It use in medicine and biology.
Geometrical optics and its laws. Refraction. Refractometry.
Determination of a refraction index of liquids with the help of
refractometer.
1
medical, stomatological
Poltava – 2016
65
The topic significance:
The majority of biological liquids have heterogeneous structures: they are
solutions of some substances: dissolved ions, various size molecules, and besides
contain the not dissolved compounds. Therefore optical properties of liquids depend on
concentration and character of included substances. Refraction index is sensitive
physical parameter, which definition gives an opportunity to receive the information
about change of the contents of these substances in a liquid, which is the certificate of
change of processes in the human body.
The refractometry which is carried out with the help of refractometers, is one of
wide-spread methods of identification of chemical compounds, the quantitative and a
structure analysis, determination of the physicochemical parameters of substances.
This method is used in the food, pharmaceutical and the biochemical industry, in
services of ecological monitoring and the state sanitary-and-epidemiologic supervision,
the scientific and educational organizations.
Specific targets:
To know the reflection and a refractive optical phenomena, their laws, use of these
phenomena in the medical equipment (α = ІІ);
To acquire physical sense of refractive index (α = ІІ);
To learn to grade a refractometer, to determine the content of material in a solution (α =
ІІ).
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Obtainable skills
Previous (providing disciplines)
Physics
Laws of reflection and refraction of light, velocity
of light spreading in air;
dielectric constant.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Refraction
Change of light ray spreading direction at ray passing through
boundary of twu mediums.
Index of refraction
The relative index of refraction shows how many times the
velocity of light v1 in the first medium is greater than the
velocity of light v2 in the second medium: v1/v2 = n2,1, that is
sinα/sinγ = v1/v2 = n2,1.
The absolute index of refraction of the medium indicates how
many times the velocity of light in vacuum c is greater than that
in the given medium v, i.e. n1 = с/v1;
n2 = c/v2.
Total internal
Total ray energy reflection, when refraction angle is more then
reflection
90°, incident angle is more then αcr
Theoretical questions to class:
1. Basics of geometrical optics.
2. Laws of geometrical optics.
3. Relative index of refraction.
4. Absolute index of refraction.
5. Phenomenon of total internal reflection. It application in medicine.
6. Refractometry. Explain how refractometry is used in medicine.
Practice work executed at class:
Study of the dependence of the index of refraction of a solution on its concentration.
66
Professional algorithms for mastering skills and habits.
Study the dependence of the index of refraction of a solution on its concentration.
Turn up the upper prism with the handle. Put a few drops of the distilled water on
the lower prism. Press the upper prism to the lower prism firmly but with care.
Direct the light from the light source (mirror, lamp, sun) to the slot. Focus the
ocular lens.
Move the spyglass upward or downward slowly until the light–shadow boundary
appears in the field of view.
If the boundary in blurred and colored, move the handhold of the equaliser up to
the disappearance of rainbow effect.
Move the ocular marks (viewfinder – three touches) to coincide with the light–
shadow boundary slow. Read the refraction index on the left scale accurate within
0,001.
Turn the upper prism up and clean the faces of both prisms with cotton. Put 3–4
drops of the solution of known concentration (initial C = 0% – clear water).
Measure the refraction index of the solution as described above.
Do the similar measurements with the other solutions of known concentration.
Each solution most be put with a separate dropper, and the prisms must be cleaned by
distilled water and dried by touch of cotton (not rub! not wipe!).
Put the obtained data into the table:
Concentration, C, %
0 1 2 3 4 5 6 7 8 9 X1 X2
Index of refraction, n
Draw the graph “concentration – refraction index”: dependence index of refraction
on solution concentration. Connect points by approximation straight line.
Measure the refraction index of the solutions of unknown concentration.
Find unknown concentrations X1 and X2 by the graph: take the unknown
concentration from the approximation graph by refraction index value.
Make the conclusion.
The contents of the topic:
Fig.1. Reflection and refraction on the
mediums border.
Fig.2. Conditions of total internal
reflection. 2 – critical angle of total
internal reflection.
The operation principle of many optical devices applied in clinics, and medical
and biological laboratories, is based on the laws of geometrical optics.
67
Geometrical (ray) optics is the branch of optics that uses the concepts of light
rays. A light ray is an imaginary line, along whichthe luminous energy propagates.
The wave nature of light is not taken into account in geometrical optics, i.e. one
may neglect the effects of light interference and diffraction. It is known that wave effects
cease to be essential when the light wavelength tends to zero (λ→0). Thus, geometrical
(ray) optics is the ultimate case of wave optics on the assumption of a very small
wavelength.
When light passes from one medium to another one, its velocity of propagation
and wavelength change, though its frequency does not.
Geometrical optics is based on the following laws:
1) the incident ray, the reflected ray, the refracted ray and the perpendicular (normal) to
the boundary of two media, which is at the point of ray incidence, are in one plane (fig.
1);
2) the law of light reflection: the angle of reflection β is equal to the angle of incidence
α;
3) the law of light refraclion: the ratio of the sine of angle of incidence α and the sine
of angle of refraction β is a constant value for given two media. This constant is called
relative index of refraction of the second medium with respect to the first one (the
relative index of refraction n2,1). The relative index of refraction shows how many
times the velocity of light v1 in the first medium is greater than the velocity of light v2 in
the second medium:
v1/v2 = n2,1, that is
sinα/sinγ = v1/v2 = n2,1.
The relative index of refraction n2,1 is equal to ratio of the absolute indices of
refraction of the second and first media, i.e. n2/n1 = n2,1.
The absolute index of refraction of the medium indicates how many times the
velocity of light in vacuum c is greater than that in the given medium v, i.e.
n1 = с/v1;
n2 = c/v2.
If light is incident on the interface from the side of the optically denser medium
(the medium with a higher absolute index of refraction), incident angle is greater than
refraction angle. When refraction angle is equal 90°, incident angle αcr is the so-called
critical angle of total internal reflection. In that case, when α> αcr, light does not pass
into the second medium, but is totally reflected from the interface (fig.2).
The value of the critical angle of total reflection is determined by the formula:
sin αcr
n
n
n , 
  , therefore, sin αcr   ,
sin 
n
n
where n1 is the refraction index of the medium, from which light falls on the
boundary, n2 is the refraction index of the medium, in which light passes after
refraction.
Phenomenon of total internal reflection is used in many optical devices.
Functioning of optical fibers is based on the effect of total internal reflection. The
branch of optics dealing with light and image transmission by optical fibers is called fiber
optics. Optical fibers are transparent fibers enclosed in a substance whose index of
refraction is less than that of the fiber. When light enters into a fiber, it reflects
repetitively and propagates along the fiber (fig. 3).
Optical fibres are the key components of endoscopes (instruments for inspection
of internal cavities – the stomach, bronchi, rectum, and others). Medicine harnesses
68
laser radiation by transmitting it along optical fibres into the internal organs for healing
tumours.
Refractometers are devices that measure the refraction indices of liquids.
In medicine, refractometers are used for determining the concentration of a
substance in a solution (for example, the content of a protein in blood serum) as in
industry (sugar concentration in syrup, purity of water etc.).
S
(A)
(B)
Fig.4. Refractometer appearance (A) and the optical arrangement of a refractometer
(B): 1 – a lighting facet of a folding prism with slot; 2 – the basic measuring prism; 3 –
an auxiliary folding prism; 3a – a delustered (matted) facet of a folding prism; 4 – an
explored fluid; 5 – the handhold of an eyepiece; 6 – an eyepiece of a telescope; 7 – the
handhold of the equaliser; 8 – Amici prisms of the equaliser; 9 – the ocular of a
spyglass; 10 – a rotary prism.
The basic elements of the refractometer are two rectangular prisms 3a and 2
made of glass with high index of refraction (n=1.72) (fig.4). The prisms face to each
other with their hypotenuse surfaces; the gap between these surfaces is about 0.1 mm.
A drop of a researched liquid is putted onto the hypotenuse facet 4 of the lower prism 2
(fig.4) and then the upper prism 3a is put on it.
At measurement the transparent liquids light on a demarcation of mediums is
guided through a small cathetus A of the auxiliary folding prism 1 (measurement in a
transmitted light), and in case of opaque mediums the mat facet С of the basic
measuring prism 2 is lit through its major cathetus (measurement in reflected light).
The light from the source S goes through the lateral surface A (small cathetus) of
the upper folding prism and falls at the hypotenuse surface B. The light scatters at this
matt facet, goes trough the layer of the researched liquid and falls to the hypotenuse
facet of the lower prism with different angles of incidence ranged from 0 to π/2.
If the refraction index of the prism is higher than that of the liquid, the refracted
rays enter in the prism 2 are only if they directed within the limits 0° to rcr – critical angle
of refraction. It results in that a part of the refractometer scale, observed in the eyepiece
6, is illuminated, while the other part is shaded. The position of the boundary between
light and shadow is determined by the critical angle of refraction which depends on the
index of refraction of the studied liquid.
69
A
B
С
A
B
Fig.5. Ray paths in refractometer at study liquids with refraction index more then at
prism glass (A), or at study liquids with refraction index less then at prism glass, or
muddy, coloured liquids with high absorption factor (B).
Refractometer-saccharimeter
At overlapping a boundary of light and dark fields with dashed line ((viewfinder,
cursor) in sight tubes on a scale quantity of n is
read directly. Right scale is graduated in units of
sugar concentration.
The boundary can be fuzzy and colored
as rainbow due to dispersion effect.
The compensator, consisting of two
dispersion prisms, allows to compensate
dispersion of the measuring prism and the
sample liquid by gyration of compensator prisms
Fig.6. Field of vision of
in the opposite direction. Boundary becomes
distinct. It do possible to measure value n2 at use
refractometer eyepiece. Ocular
of a source of a white light.
mark (viewfinder) – dashed line.
3.3. Literature recommended
Main Sources: Textbook
3.4 How to work with the literature recommended:
1. Basics of geometrical optics.
2. Laws of geometrical optics.
3. Relative index of refraction.
4. Absolute index of refraction.
5. Phenomenon of total internal reflection. It application in medicine.
6. Refractometry. Explain how refractometry is used in medicine.
Self-control material:
A. Questions and statements to bu answered:
1. Basics of geometrical optics.
2. Fundamental concept of geometrical optics.
3. Laws of geometrical optics (laws of reflection, refraction).
4. Physical meaning of relative index of refraction.
5. Physical meaning of absolute index of refraction.
70
6. Phenomenon of total internal reflection. Qualitative characteristics of
total internal reflection.
7. Optical fiber.
8. Application of total internal reflection in medicine.
9. Refractomelry.
B. Test task (α=ІІ)
Critical angle of total internal reflection for turpentine (on the interface turpentine-air) is
equal 42º 23'. Calculate light velocity in turpentine.
Answer:  2,02·108 m/s.
Materials for after auditorium independent work.
Prepare the abstract on a theme by choice: “Refraction and reflection property of
biological substances”, “Refractometry use in medicine and biology”.
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. – Poltava,
2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
71
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 7
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Optical methods. It use in medicine and biology.
Biophysics of a visual receptor.
1
medical, stomatological
Poltava – 2016
72
The topic significance:
Person receives through visual analyzer more then 90% of information about
environment. Vision gives us information about shape, size, color of outer objects and
about distances to them. It gives us possibility to orientate in space.
Peripheral part of visual analyzer is paired organs – eyes. Correspondingly,
studying of eye, its structure, function and characteristics, methods of vision hygiene is
important task.
Specific targets:
To have general knowledge of the studied topic (α=II);
To understand, to remember and to use the received knowledge (α=II);
To master concepts of visual acuity, field of vision, vision defects, correction
methods (α=II);
To take possession of measurement skills of visual acuity, field of vision (α=II);
To seize technique of experiment on determination of visual acuity by special
tables (α=II);
To seize technique of experiment on determination of field of vision – perimetry
method (α=II);
To be able to carry out laboratory and experimental work (α=III):
To measure visual acuity of every student (α=III);
To measure field of vision for mane colors (white, yellow, red, blue and green) of
one student (α=III).
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing
To
use
follows
concepts
at
tasks
decision:
disciplines): Physics;
basic concepts of optics: refraction in lenses, construction
biology.
of image in lenses;
basic concepts of eye anatomy: refracting eye apparatus,
light guiding optic system of eye, light perceiving system of
eye
Next:
Constitution and functions of structures of an eye.
Normal physiology;
Processes of accommodation and adaptation of eye.
Processes of light perception.
To explain the causes of disturbances of sight and methods
of their correction.
Methods of studying of sight characteristics.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Eye
A pair organ of sight, the composite photooptical physiological
system.
Accomodation of Property of an eye to formation on a retina is equal a sharp image
an eye
of equidistant subjects. The accomodation is carried out due to
change of a focal power of an eye at change of curvature of a
surface of a lens.
Normal viewing
Distance on which an eye is given with the different image of
distance
subjects without an excessive voltage of an accomodation (25 sm)
Visual angle
A corner which is formed by the beams which have been lined from
extreme points of an object through an optical centre of an eye.
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Sharpness of an
eye
Hypermetropia
Myopia
Astigmatism
Monocular vision
Binocular sight
Vision
Daltonism
Achromasia
Presbyopy
Light adaptation
Ability of an eye to discriminate fine details of apparent subjects.
Visual acuity is characterized by the least angular distance (visual
angle) between two points which are still accepted by an eye
separately.
Flaw of vision, the bound with a poor refractive power of an eye or
with the diminished shape of an eye globe owing to what the image
of the back-country subjects places behind of a retina.
Flaw of vision at which the sharp image of the subjects backcountry from an eye is framed in a plane which lays before a retina.
It can be consequence of the prolate shape of an eye globe or
extremely high refractive power of mediums of an eye.
Lack of the sharp image on a retina of an eye, a diffuseness and
contortion of contours of the image. It is bound with infringement of
the spherical shape of an exterior surface of a cornea or its unequal
refractive power.
Vision one eye
Vision two eyes and reception thus of the uniform conterminous
image of a subject.
Feeling (sensory sensation) which accepts light colour and structure
of world around as the image or a picture.
Daltonism is a vision deficiency, the bound with infringement of a
colour vision of the person. In that case on an eye retina the
perception of one of three base colours (red, green and blue-violet)
is lost or is attenuated. The corresponding colours are accepted as
grey.
Achromasia is the complete absence of an eye colour sensation,
color-blindness.
Presbyopy is decrease of an eye ability to an accomodation owing
to age changes (a stretching of visual muscles, and densification of
a lens). It is observed in the age of the after 40 years.
Light adaptation is adaptation of a sight organ to more intensive or
more weak lighting.
Theoretical questions to class:
1. Structura of eye: layers of eyeball envelope, structure of the anterior and
posterior parts of eye.
2. Structure of retina.
3. What is accomodation of an eye? Describe it mechanism.
4. Characterize normal viewing distance.
5. What is visual angle? It value?
6. Acute of vision.
7. Describe vision mechanism.
8. What is hypermetropia? Describe methods of it correction.
9. What is myopia? Describe methods of it correction.
10.
What is presbyopy? Describe methods of it correction
11.
What is astigmatism? Describe methods of it correction.
12.
View field.
13.
Characterize binocular sight.
14.
Mechanism of light reception.
15.
Achromatic and color vision mechanisms; characteristics and roles of
cones and rods.
74
16.
17.
18.
What is daltonism?
What is achromasia?
Mechanisms of adaptation.
Practice work executed at class.
The list of educational practical tasks which are necessary for executing on
practical training:
1. To seize habits of work with Sivtsev table.
2. To seize habits of work with perimeter.
3. To determine visual acuity.
4. To determine field of vision.
Devices and goods: the table for definition of visual acuity, the screen for occluding of
one eye. Perimeters, pointers with color circles (white, dark blue, red, green), formplans for a sketch of a field of vision.
Determination of visual acuity (distant vision).
In the table there are horizontal parallel series of letters which size decreases
from the upper lines to lower. For each lines the distance is determined, from which two
points (restricting accents of letters) are perceived at visual angle 1' (and letters - 5
minutes). Letters of the uppermost lines are perceived by a normal eye from distance of
50 meters, and inferior (or the third from below of some in Sivtsev table) - 5 meters. For
determination of visual acuity in relative unit the distance from which the patient can
read a line, is divided into distance from which it should be read under condition of
normal vision: V = d/D, where d – distance, from which patient can see certain line and
can not see lower line, D – standard distance, noted near the line. Patients discriminate
only the uppermost table line at visual acuity 0,1.
Procedure of operation:
Offer a seat the patient apart 5 meters from the table which should be well
illuminated.
Close one eye of patient by the screen.
Ask patient to term letters in the table, specifying them in a direction from top to
down.
Note last of lines which the patient could read correctly (it is supposed no more
than 25 % of errors).
Calculate visual acuity. For example, last of lines discriminated by patient is read
in norm from 10 meters. If patient stays at 5 meters from the table, him visual acuity is
equal 5/10 = 0,5.
Repeate experiment with another eye.
Visual acuity of two eyes is almost always little bit higher (on 0,1 – 0,3), than
what is achieved by everyone an eye separately.
If the patient does not discriminate from distance of 5 m even the first line of the
table, it is necessary to approach him (her) to the table while he (she) will not see clear
the first line, and then to carry out calculation by formula.
The visual acuity is tested firstly without, and then with the use of corrective
spectacles, or contact lenses.
Snellen Visual Acuity Chart
It is used when the person sits or stands at 6 meters (fig.1, A) in Great Britain.
Determination of visual acuity for near vision:
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Near vision is tested by using a test card (fig.1, B) and each eye is tested
individually. The card has number of printed paragraphs with print of varying sizes.
Each paragraph is described in terms of “points” measuring the body of the print –
where a “point” is 1/72 of an inch. In a common test, N48 is the largest type, and N5 is
A
B
Fig. 1. A) Snellen visual acuity chart. B) Snellen test card.
the smallest, which an unimpaired eye can see, held at a comfortable reading distance,
(usually 14 inches), from the eyes.
Determination of a field of vision by a perimetry method.
Visual field is determine by means of the device with the name Forster’s
perimeter, and the method, accordingly, is termed perimetry.
Desktop perimeter ПНР-2
The desktop perimeter ПНР-2 intended for examination of a field of vision.
Perimeter ПНР-2 consists of the basis, an arc, a chin seat, disk scale and linear
scale (arc scale).
During examination of a vision field
of one eye it is necessary to ungear
another eye with the help of blinder, which
enters a complete set of the device.
The desktop perimeter ПНР-2 is
completed with one set of white and color
objects for perimetry (with blinder) and
plans of a sinistral and dextral fields of
vision.
The sizes of a field of vision vary
considerably at various people. These
individual differences depend, for example,
Fig.2. Desktop perimeter ПНР-2.
on professional work, in particular, from
exercising by various kinds of sport. Boundary of a
field of vision is much wider at football players,
hockey players, volleyball players and other
representatives of game sport kinds, than at people,
which are not occupied with sports.
The visual field is incremented with the years
also. The visual field especially intensively develops
in preschool and younger school age. So, for
example, for a period from 6 till 7,5 years of a visual
field increases in 10 times. In the age of 7 years it
makes 80 % from the sizes of a field of vision of the
Fig.3. Covering of visual field of right
adult.
and left eyes. Areas of achromatic
(outer curve) and chromatic (inner
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curve) vision are shown.
Expansion of a field of vision is prolonged up to 20 - 30 age. In an old age of
Fig.4. Visual fields of left eye.
The dot line shows a visual field for a white. Blue - a visual field for blue colour;
Red - a visual field for red colour; Green - a visual field for green colour.
boundary of a field of vision converge a little. This waist goes non-uniform on all
directions, has no direct correlation with the years and depends on lines of factors,
including from an occupation.
A color (chromatic) and achromatic visual fields are discriminated.
The achromatic visual field more chromatic, that is is greatest a visual field for a
white – for the mixed colour. It explains that rods, sensing to all visual beams and
accepting not colour, but light, are in major quantity on periphery of a retina.
Boundaries of an achromatic field of vision make: outward approximately 100º,
inward and upward – 60º, and downward – 65º.
For various colours of a visual fields are unequal also. The visual field for yellow
colour is little bit less, than for white, for dark blue colour is even less, further there is a
red colour and the narrowest visual field is for green colour (see on fig. 4).
Many individuals with a retinal dystrophy or degeneration will experience loss of
their peripheral (or side) vision. Individuals with macular dystrophy may have blind spots
in their central vision. In clinic, it is necessary to measure this loss with a visual
field test.
1. Determination of visual acuity
Carry out in such sequence:
1. Offer a seat the patient apart 5 meters from the Sivtsev table (russian analogue of
Snellen visual acuity chart) which should be well illuminated.
2. Close one eye of patient by the screen.
3. Ask patient to term letters in the table, specifying them in a direction from top to
down.
4. Note last of lines which the patient could read correctly (it is supposed no more than
25 % of errors).
5. Calculate visual acuity.
6. Repeate experiment with another eye.
7. Fill the table:
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#
Name
The report of examination
Visual acuity for a dextral eye (in the Visual acuity for a sinistral eye
conditional units)
(in the conditional units)
1.
2.
3.
4.
5.
2. Determination of a field of vision
Carry out in such sequence:
1. Seat a patient before perimeter with a back toward light source.
2. Chin set on chin seat. Change position of chin seat in order to exact allocation of
pointer of eye-socket lower edge.
3. Close other eye.
4. During all examination patient must look by open eye on the white point in the
center of arc.
5. Set perimeter arc in horizontal position.
6. Move white pointer mark from periphery to the center of arc.
Arc scale is graduated in degrees.
Note angle, at which white pointer mark appears in patient field of vision.
7. Use every color pointer marks for determination of chromatic perceptibility zones.
Not warn patient about used color. Move pointer till patient will call color correctly;
do not stop at patient mistakes. Note corresponding angles.
8. Carry out this experiment from other side of arc.
9. Set perimeter arc in vertical position.
10. Repeat experiments from both sides of arc.
11. Rotate perimeter arc on 45° and 135° by order; repeat experiments from both sides
of arc.
12. Create achromatic and chromatic fields of vision.
13. Repeat experiments for other eye.
14. Note points (black and colors) on the axes on the scheme in your note-book with
distances from the center of scheme corresponding to angular visual field borders of
the patient. See the sample of the scheme on fig.5.
15. Connect points with one color for obtaining of limiting curves for visual fields for
studying colors.
78
Fig.5. Form for visual fields of left eye with the sample of graph.
3. To draw a conclusions.
Do recommendations about necessities of further examination by a doctor; about
necessities of exercises for vision correction.
The content of the topic:
The human eye structure is shown in Fig. 6. A human eye has spherical form with
diameter d=23 mm. The eyeball contains three coats (or layers): outer, middle and
internal, which are called sclera, choroid and retina correspondingly. The eyeball is
divided into two cavities, anterior and posterior, by the lens. Anterior cavity is divided
into two chambers, anterior and posterior, by the iris.
Outer coat of the eyeball sclera or fibrous coat protects the eyeball and assists in
maintaining its shape. Six exterior muscles are attached to the sclera; they turn eyeball
and enable to look left, right, up and down.
79
Fig.6. The human eye structure.
The front part of the sclera is called the cornea. Light enters the eye through the
cornea. The cornea is transparent, and it has a bigger curvature and strength than the
remaining part of the sclera. The relative index of refraction equals n=1,38; the focal
power approximately equals to 40 dptr.
Cornea is mostly a refracting part of the eye, so its external surface borders on
air and its internal surface borders on aqueous humour (a watery fluid, which fills the
anterior chamber of the eyeball). Near 70% of the total focusing of the eye happens at
light passing through cornea.
Aqueous
humour
is
a
transparent liquid with optical
properties like those of water,
n=1,33.
The middle layer of the
eyeball is the choroid. The
choroid is behind the retina and,
at the front of the eye, forms the
ciliary
body.
It
contains
numerous blood vessels. Its
function is to absorb light to
prevent internal reflection in the
eyeball
and
to
provide
nourishment for the retina, to
supply the eye with nutrients
Fig. 7. Eye accomodation principle.
and oxygen, to remove waste.
The choroid is continuous with the iris in the front of the eye.
The iris is a thin diaphragm that lies behind the cornea. Iris determines the
colour of a human's eyes. There is a small aperture – the pupil – the opening in the
centre of the iris. Light enters the eye through the pupil. Pupil dilates and constricts to
regulate the light that reaches the retina.
The space between the cornea and the iris is called the eye anterior chamber.
80
The anterior chamber is filled with a liquid whose index of refraction is almost equal to
the index of refraction of water (n=1,33). This liquid is called the anterior humour or
aqueous humour. It is the watery liquid at the front of the eye, secreted mainly by the
ciliary body.
The ciliary body comprises two parts – the ciliary process and the ciliary
muscle. Ciliary muscles causes the lens to change shape. If the eye is focusing on a
distant object the muscles relax, causing the ligaments to tighten and the lens to
lengthen. When we focus on an object nearby the muscles tighten, the ligaments
slacken, and the lens shortens.
There is a crystalline lens (or just lens), which is situated immediately behind
the pupil. The crystalline lens is a transparent elastic structure. It has the shape of a
biconvex (converging) lens. It refracts light onto the retina. The focal power of the
crystalline lens at rest is about 20 dptr; relative index of refraction is 1,44.
The structure of the lens is very interesting. It consists of a number of transparent
layers just like an onion.
The posterior camera of the eyeball is behind the crystalline lens. It is filled with a
transparent jelly-like substance called vitreous humour. Its relative index of refraction
is 1,33. Vitreous humour helps maintain the shape of eyeball and assists in the
refraction of light.
All these parts of the human eye form a light conducting system of eye.
The innermost layer lining the inside of the eyeball is retina. It is composed of
nervous tissue and does not cover the front region of the eyeball. The retina contains
photoreceptors, i.e. the retina serves as the light perceiving system of the eye.
The total focal power of the eye at rest is Deye = 63÷65 dptr. Thus, among all the
parts of the light conducting system the cornea has the maximum focal power.
The process of eye adaptation to clear vision of objects located at different
distances is called accommodation. During accommodation, the lens curvature
changes to alter its optical power. When the eye muscles are stressed, the crystalline
lens becomes rounder, making the eye focal power to increase to 70 dptr (at this the
focal power of the crystalline lens run up about 30 dptr).
Eye accommodation for clear vision of objects, which are no more than 25 cm
from the eye, requires no excess tension of the eye. Therefore, man usually tends to
locate the object being viewed at this distance from the eyes. The distance of 25 cm is
called the distance of best vision.
The least distance from the eye to the object, at which one can get its clear
image on the retina, is called eye's nearest point or the nearest point of clear vision.
People can have congenital defects of the fight conducting system, or those
acquired due to age. These are myopia, hypermetropia and astigmatism.
Myopia (nearsightedness, shortsightedness). An eye has too little refractive
power to focus light onto retina has a refractive error. A myopic eye has too much power
so light is focused in front of the retina (the focal length of the lens is too short or eyeball
is too long). At myopia (short-sightedness), the image of the viewed object is formed in
front of the retina rather than on it. The most frequent cause of myopia is a prolonged
form of the eyeball.
Refractive myopia occurs less frequently. It is related to the excessive refracting
ability (curvature) of different elements of the eye light conducting system. For myopia
correction, it is necessary to decrease the eye's optical power; for this, concave lenses
(glasses, contact lenses) are used.
Hyperopia (hypermetropia, farsightedness, longsightedness). Conversely a
hyperopic eye focuses beyond the retina. At hypermetropia (long-sightedness), the
image of the viewed object is formed behind the retina rather than on it.
The cause of presbyopia, which occurs most frequently, is loss of lens elasticity.
81
The lens fails to change its form to a sufficient extent, thus disturbing the process of
accommodation. Sometimes hypermetropia is related to the shortened size (oblate
form) of the eyeball. To correct hypemetropia, it is necessary to increase the optical
power of the eye; for this convex lenses are used.
Presbyopia. As people grow older, the lens hardens and does not return to its
rounded shape when the ciliary muscles contract, producing the age related
farsightedness called presbyopia. It is accompanied by short-sightedness
manifestations as result of lack of lens flattening restoration at survey of distant objects.
At astigmatism, the curvature of the eye's refracting surfaces is unequal in
different meridian planes, for example, in the vertical and horizontal ones. Due to this,
A
B
Fig.8. A) Myopic eye and correction of myopia with lens.
B) Hyperopic eye and correction of hypermetropia with lens.
the rays, which are incident on the eye in different planes, are focused in different ways,
and a blurred picture is received by the retina.
To correct astigmatism, cylindrical lenses are used. They have a curvature only
in one of the meridian planes, thereby providing equal refraction of the rays, which are
incident on the eye in different planes. Note that astigmatism is corrected relatively
easily in the case of simple astigmatism, i.e. when the planes of maximum and
minimum curvature are mutually perpendicular. If these planes are not perpendicular,
the case is squinting astigmatism, making it considerably harder to select correcting
lenses.
The eye's light perceiving system is formed by vision cells (receptors) arranged
on the retina. Man has two kinds of vision cells differing in form, which is reflected in
their names, viz. rods and cones. The number of rods on the retina is about 130
million, and that of cones is about 7 million. The rods and cones are irregularly
distributed over the retina. There are mainly cones in the macula lutea.
82
In the visual center of the eye there is a slight depression in the retina less than
2 mm wide, the fovea centralis (the Latin fovea means "small pit"). The fovea provides
the perception of contrast edges at an extremely high level of detail within a visual field
approximately 1,5° wide — the width of three full moons. The fovea is slightly displaced
from the visual
axis (the focal
point behind the
lens) away from
the nasal side of
each eye. As a
result the fovea
locates
under
the image of
relatively close,
centrally fixated
objects. It allows
us to determine
not
only
distances
(binocular vision)
yet many details
of target objects.
The
number of cones
decreases with
Fig.9. Retina structure.
an increase in
the distance between the macula retinae and the retina periphery, whereas the number
of rods increases under these conditions. Visual receptors are only absent in that area
of the retina where the optic nerve enters the eye. This area is called the black spot.
The line, which passes through the optical centre of the lens and the centre of the
macula lutea, is called the fine of vision. The line of vision forms an angle of
approximately 5° with eye's principal optical axis.
The cones make the human eye able to distinguish colors, i.e. they form the
apparatus of colored daylight vision. They lack very high photosensitivity, so they
require sufficiently bright light for functioning. The rods do not distinguish colors, but
they possess very high photosensitivity. They function sufficiently well at twilight when
lighting conditions are low, and the cone apparatus does not function. So, the rods form
the apparatus of achromatic twilight vision.
The maximum total sensitivity of cones is in the yellow-green band of the
spectrum and it corresponds to light with the wavelength of λ = 555 nm. This is because
the spectrum of solar radiation incident on Earth also has a maximum in this wavelength
band.
The maximum sensitivity of rods corresponds to light with the wavelength of
λ = 510 nm. This is because the rods function mainly in twilight, when lighting is
provided by light scattered in the upper layers of the atmosphere. As will be shown
further in detail, light is scattered more when its wavelength decreases.
Human's ability to distinguish colors is based on the normal eye having three
groups of cones on the retina, which have maximum sensitivity at the wavelengths of
λ= 445; 535 and 570 nm, i.e. in the blue, green and red bands of the spectrum. The
brain distinguishes colors according to the degree of exciting of one or other group of
cones. Disturbed functioning of one of the groups of cones causes such a disease as
daltonism, when a person fails to distinguish, for example, red and green colours.
83
The eye's ability to adapt vision at different brightness levels is called
adaptation. The eye regulates the quantity of light, which arrives to the retina, because
for normal functioning of visual cells their lighting must be within certain limits.
Adaptation is effected by the following mechanisms: 1) change of pupil diameter within
2 to 8 mm; 2) change of concentration of the photosensitive substance contained in the
visual receptors, its decomposition causing receptor excitation.
Visual acuity reflects ability of an eye optical system to build a sharp image in a
retina, that is characterizes spatial resolving ability of an eye. It is measured by
definition of the least distance between two points, sufficient that they did not merge,
that beams from them got on different receptors of a retina.
As criterion of visual acuity the angle serves, which is formed between the beams
going from two points of a subject to the optical centre of the eye, – a visual angle
(angle of vision). The eye distinguishes an object if the angle of vision is not less than
a certain minimum value, because to distinguish two points of an object as two distinct
points, the rays from these points should arrive to two different cones (or rods, but
cones prevail in the eye optical centre). The minimum angle of vision is equal to 1' for
the normal eye. The less this angle, the higher visual acuity. Acuity of vision is equal to
1 unit in this case. At some people visual acuity can becomes less unit (for example, at
myopia or some other infringements of sight the sharpness worsens). At children till 15
years visual acuity raises with the years. At youth and adults visual acuity can be more
than unit.
Age changes of visual acuity at normal refractive properties of an eye
Age
Visual acuity (in conditional units)
1 week
0,003
1 year
0,45
3 year
0,75
7-8 year
0,96
15 year
1,15
Adults
1,00
Except for visual acuity the major spatial characteristics of the visual analyzer is
the visual field.
The field of vision is termed space, all which points are visible at the fixed state of
an eye. The visual field determines substantially throughput capacity (transfer
capability) of the visual analyzer, that is that maximum quantity of the information
which organs of sight for unit time are capable to register. Between the sizes of a field of
vision and throughput capacity of the visual analyzer there is a direct dependence - the
more a visual field, the more its throughput capacity.
Self-control material ( Tasks for self-checking):
A. Questions to be answered:
1. General eye structure (α = І)
2. Light guiding optic system of eye (α = І)
3. Refracting eye apparatus. (α = І)
4. Light perceiving system of eye (α = І)
5. Structure of retina (α = І).
6. What is acuity of vision? (α = І)
7. What is viewfields? What is characterized by viewfields? (α = ІІ)
8. What influes on viewfield size? (α = ІІ)
9. For what color viewfield is maximal, for what – minimal? Why? (α = ІІ)
10. Infringements of sight. Methods of them corrections (α = І)
11. Peculiarities of photopic and scotopic vision. (α = І)
12. Accommodation of eye. (α = І)
84
13. Adaptation of eye. Types of adaptation. (α = І)
14. Hygiene of vision. (α = І)
B. Test tasks to be done:
1. Patient discriminates last of lines, which is read in norm from 30 meters.
Patient stays at 5 meters from the table. Calculate visual acuity.
2. Patient stays at 3 meters from the table and discriminates only upper line,
which is read in norm from 50 meters. Calculate visual acuity.
Materials for after auditorium independent work.
Prepare the abstract on a theme by choice: “Modern methods of correction of
infringements of sight”, “Methods of prophylaxis of infringements of sight”.
Literature recommended
Main Sources:
─ Lecture
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. – Poltava, 2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for students,
physicians and researchers. Nico A.M. Schellart. – Department of Biomedical
Engineering and Physics Academic Medical Center University of Amsterdam.–
Amsterdam.– 2009 (electronic book).
85
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 7
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Optical methods. It use in medicine and biology.
Optical centered system. Lenses. Construction of
image in lenses. Optical microscopy and its
quantitative characteristics. Learning characteristics of
the light microscope. Measurement of sizes of small
objects with the help of an optical microscope.
1
medical, stomatological
Poltava – 2016
86
The topic significance:
As the history shows, major achievement in biological researches, and in
other branches of natural sciences, are connected to use of new physical methods.
Discovery of optical microscope has given to such surprising turn of opening, thai its
importance for a science are heavy for overestimating. In biology, at once after
discovery of optical microscope in XVII century, was find out a structure of alive
cell, the microorganisms, elements of blood etc. At the same time optical microscopy
is one of main making of biophysical experiment.
Specific targets:
─ To have general knowledge of the studied topic (α=II);
─ To understand, to remember and to use the received knowledge: optic laws,
refraction in thin lenses, creation of images in lenses systems (α=II);
─ To master concepts of microscopic observation (α=II);
─ To seize habits of work with light microscope (α=II);
─ To seize technique of experiment on determination of microscopic object sizes
(α=II);
─ To seize habits of work with object – micrometer and ocular micrometer (α=II);
─ To be able to carry out laboratory and experimental work (α=III).
─ To measure sizes of microscopuc samples (α=III).
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing disciplines):
To know basic concepts of optics: refraction in
physics, biology
lenses, construction of image in lenses.
To know special kinds of microscopy; electron
microscopy, its kinds; atomic force microscopy.
To describe them.
The subsequent disciplines:
Concept of microscopic studies.
general biology;
To use these concepts at the decision of tasks;
microbiology histology
Speak about this topic, to prepare sample to
experiment.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Resolution
Resolution is the minimal distance on which there are two
points shown to a microscope separately.
Numerical aperture
The size n·sinφ, where n – refraction index of environment
between a sample and an objective, φ – half of entrance angle of
an objective (angle between extreme beams of the conic light
beam which is entered in an objective).
Than NA is more and the wavelength the less, the less resolved
details of researched object.
Contrast of the image Contrast of the image is a distinction of brightnesses of the image
and a background.
Chromatic
Chromatic aberrations are caused by that light waves with
aberrations
different wave length are focused in different points on an optical
axis. In result the image appears painted.
Spherical aberrations Spherical aberrations are connected by that light which is taking
place through the center of an objective, and light going through
its peripheral part, is focused in different points on an axis. In
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result the image appears indistinct.
In them chromatic aberrations are suppressed by means of glass
elements with the different dispersion, extreme beams of a seen
spectrum providing a convergence – dark blue and red – in one
focus.
Apochromatic
Objectives with the most complex color correction. In them not
objectives
chromatic aberrations are only almost completely eliminated, but
also correction of spherical aberrations is executed not for one,
and for two colors.
Theoretical questions to class:
1. The key part of a light microscope. (α = І)
2. Creation of image by objective and eyepiece (α = ІI)
3. Rays pathes in microscope (α = ІI)
4. Microscope magnification. (α = ІI)
5. Resolving limit of a microscope. (α = II)
6. Causes of aberrations appearance, methods of them reduction.
7. Polarization microscopy.
8. Luminescent microscopy. (α = І)
9. Microphotographing and microfilming. (α = І)
10. Dark-field microscopy. (α = І)
11. Phase-contrast microscopy. (α = І)
12. Microscopy with immersion. (α = І)
13. Binocular microscopy (α = І)
14. Electron microscopy. (α = І)
15. Fiber optics, including use in medicine (α = І)
Practice work executed at class:
Professional algorithms (instructions, reference cards) concerning mastering habits and
skills:
№
Maun tasks
Recommendations
1
2
3
1. To seize a procedure
To familiarize with outward of the device, to determine the
of operation with the quantitative performances on an objective, an eyepiece; to
light microscope.
examine an object-micrometer. To provide good illumination the
subject stage.
Achromatic objectives
2.
3.
To determine the
graduation
mark
(scale-division value)
of
an
ocular
micrometer.
An object - micrometer is glass or plastic plate with scale
(squares). Scale-division value can be 1 mm or 0,01 mm
usually.
An eyepiece [ocular] micrometer is glass or plastic plate with
linear scale. Ocular micrometer is allocated between ocular
lenses in the plane of intermediate image formed by objective.
In the ocular image of this scale is visible, and it overlaps
sample image.
To dispose an object-micrometer with the known value of
division (Mob =1 mm) on the stage. To determine, how many
divisions (n) of an ocular micrometer are coated with particular
number N of divisions of the image of a reference scale (objectmicrometer): ocular micrometer scale-division value Moc = N/n.
Iterate 3 times. Calculate average value.
To determine the size To dispose a microscopic object on the stage, to receive its
of a microscopic precise image, to sketch it, then with the help of the stage
object.
controls handles, to bring a crossroads, all over again on one,
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and then on the second end of a microscopic object. In both
cases to make a scale reading of a micrometer m1 and m2; to
l = m1–m2. Calculate object size L = l × Moc.
Execute measurings 5 times, bring results into the copybook in
Table 1.
Fig.10. Ocular-micrometer scale against a background of cells.
Table 1
N
Object
N
n
Moc, mm
l, mm
L, mm
1
2
3
4
5
Contens of the topic.
Light microscope - the typical models use compound lenses and light to magnify objects
images. The lenses refract the light, which makes the object beneath them appear
closer.
Fig.1. Microscope scheme.
The key part of a light microscope is its drawtube that encases two collapsible
lens systems: the objective and the eyepiece. The path of the rays in the microscope is
shown in Fig. 1.
The objective with a focal distance fob which is equal to several millimeters, and
an eyepiece with a focal distance foc which is equal to several centimeters. Object AB
places directly in front of focus fob of the objective. Its image A1B1 originates at the
distance greater than 2fob. As clear from the design, the objective creates a magnified,
inverted, and real image.
The eyepiece is located thus that this image A1B1 was behind eyepiece focus foc.
The final image of the object A2B2 (studied in the microscope as a whole) is
magnified, inverted, and virtual. In is located on the best vision distance (25 cm for a
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normal eye).
Total magnification of microscope V is product of separate magnifications of
objective V1 and eyepiece V2:
(1)
V  V  V   S  l ,
ff
where l is optical length of a tube (distance between focal points fob and foc), fob
and foc are focal distances of the objective and an eyepiece accordingly, S is distance of
the best sight.
Phenomenon of light diffraction limits maximum possible magnification. A
resolving limit of a microscope (d) is the minimum distance between two points, which
can be viewed in a microscope as two distinct points.
The formula for calculating the resolving limit of an optical microscope can be
derived from the formulae, which describe the diffraction phenomenon. A resolving limit
d is equal:
d  , λ ,
n sin α
(2)
where λ – is wavelength of used light in vacuum, n – refraction index of medium
between object and objective, α is the aperture angle – angle between ultimate rays of
light beam, which left from object point and hit to the objective.
Wavelength λ is limited for visual light, therefore minimal d is equal approximately
0,2 mkm (it corresponds to maximal magnification nearly 1500 times.
Increase of the resolving limit can be achieved by diminution of wavelength.
There are two main methods. For example, it can be using ultraviolet light and quartz
lenses (transparent for ultraviolet radiation) in microscope. Common glass, which is
used for making light microscope lenses, is opaque to ultraviolet radiation. Obtained
image must be photographed or transformed into visible form by luminescent screen or
by image converter tubes.
Scanning Electron Microscope allow scientists to view a universe too small to
be seen with a light microscope. SEMs don’t use light waves; they use electrons
(negatively charged electrical particles) to magnify objects up to two million times. In
electron microscope for obtaining of image accelerated high-energy electrons beams
are used. Due to dual particle-wave properties these electrones behave like very short
wave light and allow to obtain images with nanometer size details. Transmission
Electron Microscope – also uses electrons, but instead of scanning the surface (as
with SEM's) electrons are passed through very thin specimens.
The image formed by the microscope during ordinary microscopy is virtual. A real
image is formed on the retina because the eye, which has a sufficiently high optical
force, collects diverging rays, which exit the eyepiece. If one attempts lo obtain an
image on a screen rather than on the retina, he must make the image formed by the
microscope real. It can be formed by increasing the distance between the objective and
the eyepiece so that the image formed by the objective is located far from the eyepiece
at a distance greater than the focal distance, rather than between the eyepiece and the
focus, as in ordinary microscopy. If in so doing the image is formed on the screen, this
is microprojection; and if the image is formed on a photographic plate, this is
photomicrography [microphotography].
Brightfield - This is the basic microscope configuration (the images seen thus far
are all from brightfield microscopes). This technique has very little contrast; in the
images you've seen so far, much of the contrast has been provided by staining the
specimens.
Darkfield - This configuration enhances contrast.
Phase contrast - This technique is best for looking at living specimens, such as
cultured cells.
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Fig.2 Phase-Contrast Light Pathways.
In a phase-contrast microscope, the annular rings in the objective lens and the
condenser separate the light. The light that passes through the central part of the light
path is recombined with the light that travels around the periphery of the specimen. The
interference produced by these two paths produces images in which the dense
structures appear darker than the background.
During incidence on a transparent object, a fraction of light passes through this
object, and a fraction scatters on the object elements distinguished by the refraction
coefficient. The rays passing through the object and those scattered differ in phase
slightly, and when they meet on the screen, they interfere. Since their phase differences
are small, in case of transparent objects, the rays create illumination on the screen,
which differs little from that in adjacent points of the screen.
For augmentation of phase contrast of adjacent points special methods are used. At
normal incidence of parallel light rays on the object, rays passed through object without
scattering go directly pass through the objective focus. A phase plate, which increases
the optical path of rays, is placed in the focus area. It can to increase illumination of the
adjacent points as result of interference. It is necessary to use special objectives and
special condensers.
The other way is using of phase plate with an aperture in its centre. In so doing, the
optical length of the path changes to change the phase of rays scattered on the object,
rather than that of rays, which have passed directly through the object.
Differential interference contrast (DIC) - DIC uses polarizing filters and prisms
to separate and recombine the light paths, giving a 3-D appearance to the specimen.
Stereoscope - this microscope allows for binocular (two eyes) viewing of larger
specimens. (The spinning microscope at the top of this page is a stereoscope).
Polarization - The polarized-light microscope uses two polarizers, one on either
side of the specimen, positioned perpendicular to each other so that only light that
passes through the specimen reaches the eyepiece. Light is polarized in one plane as it
passes through the first filter and reaches the specimen. Regularly-spaced, patterned or
crystalline portions of the specimen rotate the light that passes through. Some of this
rotated light passes through the second polarizing filter, so these regularly spaced areas
show up bright against a black background.
Fluorescence - This type of microscope uses high-energy, short-wavelength
light (usually ultraviolet) to excite electrons within certain molecules inside a specimen,
causing those electrons to shift to higher orbits. When they fall back to their original
energy levels, they emit lower-energy, longer-wavelength light (usually in the visible
spectrum), which forms the image.
The fluorescent molecules within the specimen can either occur naturally or be
introduced. For example, you can stain cells with a dye called calcein/AM. By itself, this
91
dye is not fluorescent. The AM portion of the molecule hides a portion of the calcein
molecule that binds calcium, which is fluorescent. When you mix the calcein/AM with
the solution bathing the cells, the dye crosses into the cell. Living cells have an enzyme
that removes the AM portion, traps the calcein within the cell and allows the calcein to
bind calcium so that it fluoresces green under ultraviolet light. Dead cells no longer have
this enzyme. Therefore, living cells will fluoresce green, and dead cells will not
fluoresce. You can see the dead cells in the same specimen if you mix in another dye
called propidium iodide, which only penetrates the dead cells. Propidium iodide binds to
DNA in the nucleus and fluoresces red under ultraviolet light. This double-dye technique
is used in toxicology studies to determine the percent of a cell population that is killed
when treated with some environmental chemical, such as a pesticide.
Fluorescence-microscopy techniques are useful for seeing structures and
measuring physiological and biochemical events in living cells. Various fluorescent
indicators are available to study many physiologically important chemicals such as
DNA, calcium, magnesium, sodium, pH and enzymes. In addition, antibodies that are
specific to various biological molecules can be chemically bound to fluorescent
molecules and used to stain specific structures within cells.
Microscopy method
Devices and goods:
A light microscope, stage micrometer, tooth microsection, human hair, thin plant leaf, onion
scales, blood smear.
Coarse focus = rough (crude) focusing = coarse adjustment.
Sample = specimen.
Fig.3. Optical microscope cross-section.
Modernt variants of microscopes are represented on follows pictures.
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Fig.4. Optical microscope overview (variantes).
If stage has round shape with incisions over the entire side, it is mean, that stage
can be rotated. In other case coaxial stage controls handle can be at side of stage.
Small handles on sides of the stage are control of stage sliding movement right–left
and forward–backwards usually.
The parts of a light microscope
A light microscope, whether a simple student microscope or a complex research
microscope, has the following basic systems:
─ specimen control - hold and manipulate the specimen;
─ stage - where the specimen rests;
─ clips - used to hold the specimen still on the stage (Because you are looking at a
93
magnified image, even the smallest movements of the specimen can move parts of
the image out of your field of view.);
─ micromanipulator - device that allows you to move the specimen in controlled, small
increments along the x and y axes (useful for scanning a slide);
─ Illumination - shed light on the specimen (The simplest illumination system is a
mirror that reflects room light up through the specimen.);
─ lamp - produces the light (Typically, lamps are tungsten-filament light bulbs. For
specialized applications, mercury or xenon lamps may be used to produce ultraviolet
light. Some microscopes even use lasers to scan the specimen.);
─ rheostat - alters the current applied to the lamp to control the intensity of the light
produced;
─ condenser - lens system that aligns and focuses the light from the lamp onto the
specimen;
─ diaphragms or pinhole apertures - placed in the light path to alter the amount of light
that reaches the condenser (for enhancing contrast in the image).
Lenses – form the image:
─
objective lens - gathers light from the specimen;
─
eyepiece - transmits and magnifies the image from the objective lens to your
eye;
─
nosepiece - rotating mount that holds many objective lenses;
─
tube - holds the eyepiece at the proper distance from the objective lens and
blocks out stray light.
Focus - position the objective lens at the proper distance from the specimen:
─
coarse-focus knob - used to bring the object into the focal plane of the
objective lens;
─
fine-focus knob - used to make fine adjustments to focus the image.
Support and alignment:
─
arm - curved portion that holds all of the optical parts at a fixed distance and
aligns them;
─
base - supports the weight of all of the microscope parts.
The tube is connected to the arm of the microscope by way of a rack and pinion
gear. This system allows you to focus the image when changing lenses or observers
and to move the lenses away from the stage when changing specimens.
Light microscopes can reveal the structures of living cells and tissues, as well as
of non-living samples such as rocks and semiconductors. Microscopes can be simple or
complex in design, and some can do more than one type of microscopy, each of which
reveals slightly different information. The light microscope has greatly advanced our
biomedical knowledge and continues to be a powerful tool for scientists.
Some Microscope Terms
─ Depth of field - vertical distance, from above to below the focal plane, that yields an
acceptable image.
─ Field of view - area of the specimen that can be seen through the microscope with a
given objective lens.
─ Focal length - distance required for a lens to bring the light to a focus (usually
measured in microns).
─ Focal point/focus - point at which the light from a lens comes together.
─ Magnification - product of the magnifying powers of the objective and eyepiece
lenses.
─ Numerical aperture - measure of the light-collecting ability of the lens.
─ Resolution - the closest two objects can be before they're no longer detected as
separate objects (usually measured in nanometers).
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Magnification
Sign “x” marks magnification of lens.
Your microscope has 3 magnifications: Scanning (minimal), Middle and High.
Each objective will have written the magnification. In addition to this, the ocular lens
(eyepiece) has a magnification. The total magnification is the ocular magnification
Ч objective magnification.
Dark stripe is used for oil immersion objective marking.
Objective
Ocular lens
Total
magnification
magnification
Magnification
Scanning (low power)
8x
7x
56x
Middle Power
40x
7x
280x
70x
490x
High Power (immersion
or
7x
or
objective use)
100x
700x
Types of objective and ocular lenses used in USA and Britain have other
magnifications and marking (next characteristics): the objective lenses, located
on the rotary nosepiece, provide 4 different degrees of magnification (British
notation):
Name
Characteristics
Magnifying power
Scanning power
shortest objective, red stripe
4x
Low power
next shortest, yellow stripe
10x
High-dry power
intermediate length, blue stripe
40, 43 or 45x
Oil immersion
longest, black stripe
100x
The ocular lens, located nearest to your eye, has a magnification power
of 10x.The total magnification is determined by multiplying the power of the
objective by the power of the ocular. (For example, 4x times 10x = 40x).
General Procedures
1. Always start and end with the Scanning Objective. Do not remove slides with the
high power objective into place – this will scratch the lens!
2. Always wrap electric cords and cover microscopes before returning them to the
cabinet. Microscopes should be stored with the Scanning Objective clicked into
place.
3. Always remove the sample from the stage before microscope transportation.
4. Always carry microscopes by the holder (arm) and set them flat on your desk.
Focusing Specimens
1. Set optimal illumination of field of vision in eyepiece.
2. Always pull down microscope observation tube under observation from the side, do
not look into the ocular. You can damage lense and slide (sample), as object-plates can
have various thicknesses.
3. Always start with the scanning objective. Odds are, you will be able to see something
on this setting. Use the Coarse Knob to focus, image may be small at this magnification,
but you won't be able to find it on the higher powers without this first step. Do not use
stage clips, try moving the slide around until you find something.
4. Once you've focused on Scanning, switch to Low Power. Use the Coarse Knob to
refocus. Again, if you haven't focused on this level, you will not be able to move to the
next level.
5. Now switch to High Power. (If you have a thick slide, or a slide without a cover, do
NOT use the high power objective). At this point, ONLY use the Fine Adjustment Knob
to focus specimens.
6. If the specimen is too light or too dark, try adjusting the diaphragm.
7. If you see a line in your viewing field, try twisting the eyepiece, the line should move.
95
That's because its a pointer, and is useful for pointing out things to your lab partner or
teacher.
Ending
1. Store microscopes with the scanning objective in place.
2. Wrap cords of light source and cover microscopes.
Image Quality
When you look at a specimen using a microscope, the quality of the image you
see is assessed by the following:
Brightness - How light or dark is the image? Brightness is related to the
illumination system and can be changed by changing the voltage to the lamp (rheostat)
and adjusting the condenser and diaphragm/pinhole apertures. Brightness is also
related to the numerical aperture of the objective lens (the larger the numerical aperture,
the brighter the image).
Fig.5. Image of pollen grain under good brightness (left) and poor brightness (right).
Focus - Is the image blurry or well-defined? Focus is related to focal length and
can be controlled with the focus knobs. The thickness of the cover glass on the
specimen slide can also affect your ability to focus the image -- it can be too thick for the
objective lens. The correct cover-glass thickness is written on the side of the objective
lens.
Fig.6. Image of pollen grain in focus (left) and out of focus (right).
Resolution - How close can two points in the image be before they are no longer
seen as two separate points? Resolution is related to the numerical aperture of the
objective lens (the higher the numerical aperture, the better the resolution) and the
wavelength of light passing through the lens (the shorter the wavelength, the better the
resolution).
Fig.7. Image of pollen grain with good resolution (left) and poor resolution (right).
Contrast - What is the difference in lighting between adjacent areas of the
specimen? Contrast is related to the illumination system and can be adjusted by
changing the intensity of the light and the diaphragm/pinhole aperture. Also, chemical
stains applied to the specimen can enhance contrast.
96
Fig.8. Image of pollen grain with good contrast (left) and poor contrast (right).
Depth of focus is interval of object details from the objective, in which object point
are distinct. The more magnification, the less depth of focus (fig.9).
Fig.9. Depth of focus. Bidirectional arrows show layers, in which images are distinct.
Troubleshooting
Occasionally you may have trouble with working your microscope. Here are
some common problems and solutions.
1. Image is too dark: Adjust the diaphragm (condenser), make sure your light is
on.
2. I can't see anything under high power!
Remember the steps, if you can't focus under scanning and then low power, you
won't be able to focus anything under high power.
3. Only half of my viewing field is lit, it looks like there's a half-moon in there!
You probably don't have your objective fully clicked into place.
Self-control material.
A. Questions to be answered:
1. Thin lenses kinds, light pathways in thin lenses; image forming pathways in thin
lenses.
2. To know thin lens formula.
3. To be able draw converging and diverging lenses;
4. To be able draw images in converging and diverging lenses, when object is:
a) between optical center and focus of lens;
b) between focus and double focus of lens;
c) after double focus of lens.
5. What is microscope? Describe purposes of its using in medical-biological research.
6. Name the key part of a light microscope and explain them functions.
7. To know rays pathes in microscope, creation of image by objective and eyepiece.
8. How to calculate microscope magnification? What factors influe on it? Give the
definition and write formula of microscope magnification.
9. Give the definition and explain limitations and the resolving limit of a microscope. What
is microscope resolution? Its maximal value.
10. What is numerical aperture? What is mean?
11. Give the definition and explain causes of aberrations appearance, methods of them
reduction.
12. Give the definition and explain principles of special methods of microscopy:
microphotographing and microfilming, binocular microscopy, stereoscopic (three97
dimensional) binocular microscopy, ultramicroscopy, ultraviolet, dark-field,
luminecscent microscopy, polarizing microscopy, phase-contrast microscopy,
microscopy with immersion.
13. Explain the preference of electron microscopv.
14. Explain the preference of polarization microscopy and luminescent microscopy.
15. Describe using of fiber optics in medicine.
Materials for after auditorium independent work.
Prepare the abstract on a theme by choice: “Modern methods of microscopy”,
“Electron microscopy use in medicine”, “Methods of research of live microscopic
organisms”.
Literature recommended
Main Sources:
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena.–Poltava,
2014.
Additional textbook, journals and references:
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
98
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1 year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
st
Subject matter
Module № 2
Meaningful module № 8
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Elements of quantum mechanics.
A thermal radiation and its laws. Quantitative characteristics
of a human body thermal radiation. Thermovision.
1
medical, stomatological
Poltava – 2016
99
The topic significance:
Temperature measurements are very important diagnostical methods. Wide them
using, modern them development for detail study of distribution of heat production in
patient’s body makes them study necessary for future doctor.
Any body radiates electromagnetic waves if its absolute temperature is higher
than zero. It is thermal radiation. Any body can absorb the thermal radiation of other
bodies. Emission and absorption of thermal radiation by bodies are described by some
laws.
Specific targets:
─ To acquire concepts: temperature, heat, heat irradiation, absolute black body, grey
body. (α=II )
─ To know a basic laws of body thermal irradiation (α=II).
─ To know a basic characteristics of Sun irradiation, infrared and ultraviolet irradiation
(α=II).
─ To acquaint with main methods of heat irradiation using at diagnostic (α=II).
─ To acquaint with main devices that used at thermodiagnostic (α=II).
─ To acquaint with main methods of thermal measurement (α=II).
─ To be able explain using of thermal irradiation in medicine at diagnostics (α=III).
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing
Idea of temperature. Laws of thermal movement.
disciplines):
Temperature measurements.
physics, chemistry,
To explain mechanism of thermal irradiation appearance.
biology
To use these concepts at tasks decision
The subsequent
Mechanism of heat irradiation.
disciplines:
Devices that are used in medicine.
Normal physiology
To explain mechanism of thermal irradiation using in medicine.
Pathologic physiology To adhere to safety laws.
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Radiation flux
Energy of radiation which falls at the given area during one
second.
Radiation intensity
Energy of the IR radiation, falling a unit area for one
second
Radiant emittance
Radiance (R) is the ratio of the radiation flux of thermal
radiation (Φ) emitted by a surface to the area of this surface
(S): R=Φ/S.
Radiation coefficient
Absorption constant
The capacity of a body to absorb thermal radiation is
(absorption factor)
characterized by the absorption factor.
Absorption coefficient is natural logarithm of relation passed
light stream to incoming light stream and to the distance
passed through substance.
It is coefficient, which depends on materials nature and
radiation wave lengths.
Monochromatic
Absorption constant determined for certain wavelength.
absorption constant
Black body
Body which absorbs all incident radiation.
100
Grey body
Thermography
A body having monochromatic absorption factor is less than
unity and does not depend on the radiation wavelength.
Method of registration of thermal irradiation of a body
Theoretical questions to class:
1. Causes of the thermal irradiation.
2. Thermal radiation spectrum.
3. Absorption factor. Write down and analyse the formula for absorption factor.
4. The emissive and an absorbing ability of bodies, an absolute black body.
5. Grey body.
6. Write down and analyse the formula for Kirchhoff law.
7. A Planck radiation law. Describe and explaine it.
8. Write down and analyse the formula for Stefan – Boltzmann law.
9. Wien's displacement law.
10. Thermal irradiation of human body.
11. Explain meaning of medical method of thermography.
12. A structure and a principle of action of thermographic devices.
Practice work executed at class:
The material equipment: tables, the medical thermometer, the electrothermometer, a
film for heat-indicating diagnostic.
b) The list of operations which are subject to accomplishment:
To familiarize with liquid-cristal films;
To familiarize with the block diagram of the thermograph;
To familiarize with a principle of operation of the electrothermometer.
c)
The list of practical habits with which are necessary for seizing:
To be able to take the temperature the person by the medical thermometer and
electric thermometer.
Contens of the topic.
Abbreviations:
IRI – infrared irradiation
EMF – electromagnetic field
EF – electric field
MF – magnetic field
The caloradiance (thermal radiation) is an electromagnetic radiation. It is an
information source, is used for diagnostic and treatment.
Thermal radiation takes in a spectrum of electromagnetic waves a place
between visual light and radiowaves, i.e. over the range 0,76 microns up to 1 mm.
All gamut of thermal radiation is divided into some fields (table 1).
Wave length (micron)
The name of area
0,76-1,5
Short-range IR-radiation
1,5-5,5
Short-wave IR-radiation
5,6-25
The long-wave IR-radiation
25-1000
Long-range IR-radiation
This division is conventional, but it takes into account properties of IR
radiation and its practical use. IR beams have wave and quantum properties,
spread and are absorbed by quantums. Energy of quantum depends on a wave
length:
E = hν = hc/ λ,
where Е – energy, c – velocity of light, h – the Planck constant, λ – a wave length.
101
The basic performance of IR radiation is radiated power (radiant flux) – energy
of radiation which falls at the given area during one second.
Energy of the IR radiation, falling a unit area for one second, is termed as
radiation intensity [radiation rate, strength of radiation]. Unity of intensity is W/m2 .
IR radiation is absorbed, reflected, diffracted and scattered.
Absorption. Absorption of IR beams obeys the Bouger-Beer law:
Ф = Фоеkl ,
Where Фо - a stream of an incoming radiation on material, Ф - a stream which has
passed through material, l - depth of material, k - coefficient which depends on
materials nature and radiation wave lengths (absorption coefficient).
Absorption coefficient is natural logarithm of relation passed light stream to
incoming light stream and to the distance passed through substance.
From the given formula it is clear, that uptake is promptly incremented with
magnification of depth of an immersing layer. For example, if the layer in 1 mm
attenuates radiation twice the layer depth will attenuate of 5 mm in 32 times, and the
layer of 10 mm – attenuates more, than in 1000 times.
Tissues of an organism absorbs IR radiation differently; it depends on IRI wave
length. An example can be a human skin.
Reflection. Metal surfaces well reflect as visual, and IR radiation. But the
pattern of reflection will be different and will differ from usual. The grass, leaves,
well reflecting IR radiation, seem much more lighter, the same as also an eye iris, a
dark hair. The text written by different paints, can variate in IR beams depending on
a mineral and molecular composition of a paint which are used in different views of
examination.
The human skin absorbs and reflects IR radiation differently. It is used for
recognition of dermal sicknesses in forensic medicine and criminalistics.
Refraction. The refractive index for IRI is less than for visual beams, they are
less reflected at transition from one medium in another, that it is necessary to take
into account at photographing in IR beams.
Scattering. IR beams are scattered less than visual light. The scattering of
any radiation by small particles (a fog, a dust, gas bubbles) depends by nature, size
and shapes of particles, and also on a wave length. If the particles sizes are small in
relation to a wave length of radiation, dependence is featured by the formula of
Rayleigh:
I ~ (n–l)2/(N0λ4),
i.e. a scattering in inverse proportion to the fourth power of a wave length.
Dependence on a wave length will be more weak for bigger particles. Lesser,
than for visual light, scattering of IR beams enables to use them in aeroobservations
even in requirements of the poor vision.
THERMAL RADIATION
Condition of thermal equilibrium of much body system is Kirchhoff law.
Kirchhoff law:
Relation of body radiation ability Ef,T to body absorption ability Af,T don’t depend on
body material and equal to radiation ability of absolute black body that is function of
Ef ,T
frequency and temperature:
 εf ,T ,
Af ,T
where f – wave frequency, T – absolute temperature.
The radiation flux (Φ) is energy transferred by radiation through a surface per
second (radiation power). The unit of the radiation flux is watt (W).
Radiance (R) is the ratio of the radiation flux of thermal radiation (Φ) emitted by
a surface to the area of this surface (S): R=Φ/S. The unit of radiance is watt par square
meter (W/m2).
102
Thermal radiation has a continuous spectrum.
Spectrum is set of all values of physical quantity, which characterize some
system or process. Continuous spectrum is spectrum in which all values are possible,
whithout exception. On the contrary, discontinuous [discrete] spectrum has limited
quantity of possible values.
Spectral radiance (r) is characteristics of dependence of intensity on
wavelength: r=dR/dλ, where dR is the radiance of radiation within the wavelength range
of λ to λ+dλ. The unit of the spectra! radiance is watt per cubic meter (W/m3).
The spectral radiance of a body vs. the radiation wavelength dependence is
known as the thermal radiation spectrum of this body.
Absolute black body irradiation
A black body has monochromatic absorption factor at all wavelengths is equal to
unity. A black body absorbs all incident radiation.
The temperature radiance dependence is known as the Stefan-Boltzmann law:
R = σ•T4,
where σ ≈ 5,7•10–8 W/(m2K4);
where σ – is Stefan-Boltzmann constant.
The dependence of spectral radiance of a black body on the temperature is
represented on fig.1.
Wien's displacement law:
The wavelength (λm) of the thermal radiation spectrum maximum of the black
body spectral radiance is equal to: λm 
b
,
T
where b is a constant (if T expressed in Kelvin degrees, Wien constant
b=2886•10–6m•K).
Wien's displacement law manifests in next phenomenon: bodies at habitual
temperatures (in interval -50° – +100°C) radiate energy in infrared range mainly.
From Wien's displacement law it
follows
that
the
wavelength,
corresponding to the maximum of the
thermal radiation spectrum of a body, is
completely defined by the temperature of
the body. Hence, by finding the value λm,
can be determined the temperature of a
body. This method of determining the
temperature of a body is known as
optical pyrometry.
Grey body is a body having
monochromatic absorption factor is less
than unity and does not depend on the
radiation wavelength.
Fig.1. Absolute black body irradiation at
Naturally grey bodies do not exist,
various temperatures of black body.
but some bodies within some wavelength
range can be considered grey. For example, a human body is considered grey in the
infrared range. Its absorption factor is about 0.9.
Human body produces energy in process of chemical reactions. This energy is
used for work partly and dissipates as heat partly. Production of heat in an organism is
a side effect of a metabolism processes according to thermodynamics laws. However
for homoitherm metabolic heat is necessary for maintenance of a constant level of
activity irrespective of environmental temperature as intensity of energy transmutations
grows proportionally to temperature. Normal temperature of a human body in near 37ºC
103
in so-called body core – organs that need with constant temperature of activity: brain,
heart, liver, digestive system.
Body heat interchange occurs by some ways: radiation (absorption), thermal
conduction, convection and evaporation. Heat can be radiated more than be absorbed
or conversely. Allocation of volumes of heat dissipation between these processes
depends on many factors: states of an organism (temperature, physical activity,
emotional state, etc.), states of a surrounding medium (temperature, humidity, motion of
air, etc.), clothes (a material, thickness, a shape, etc.).
The heat dissipation as the long-wave infrared irradiation emitted by a skin (in
which the conducting medium does not accept participation), is strictly featured by
Stefan-Boltzmann equation, i.e. radiation is function of the fourth degree from a Kelvin
temperature. The maximum of spectral density of an energy brightness of a body of the
person at temperature of a skin surface near 32°С is approximately equal 9,5 nm
(according to the Wien’s law) and energy loss is near 120J/s. The skin irradiates almost
precisely as much energies in a gamut of the long-wave infrared radiation, how many
«the complete emitter», or absolutely black body. In case of short-wave infrared
radiation (let out by such emitters as electroradiators or the Sun) both emitting, and
absorbing skin abilities become much less than 1 (0,5–0,8) and appear dependent from
a dermal pigmentation. Correspondingly, the Stefan-Boltzmann law is used in form for
grey bodies:
R = α•σ•T4, where α is absorption coefficient of skin or clothes.
As body allocates in environment with temperature differed from absolute zero,
exact form of Stefan-Boltzmann law is: R = α• e• σ• (T4–T04), where T – body
temperature, T0 – environment temperature, e = 0,98 – coefficient of skin emittance.
Absorption coefficient α for cotton fabric is 0,73, for wool or silk – 0,76.
Radiation from open body parts can consist near 50% of heat dissipation.
Use of thermal radiation in medicine.
Development and improvement of devices and electrooptical transducers has
enabled to use photographing, a microscopy, a spectrometry in IR beams in medical
practice widely. The infra-red photography is used for survey of the surface veins.
The light absorption by blood depends on contents in it oxyhemoglobin (oxygenated
hemoglobin – compound of a haemoglobin with oxygen) and a reduced haemoglobin.
In IR area these colorants absorbs weakly and almost equally. Therefore blood
rather transparent for IR beams irrespective of a extent of a haemoglobin saturation.
A scattering by blood is small also. IR radiation, which impinges on a blood vessel,
transits through them and inpours into more deeper layers of a skin or subcutaneous
adipose tissue, than in those places where vessels are not present. Therefore the
field where the vein transits, will differ in a photo. Visibility of veins appreciably
depends on specific features of the person (amount of blood in vessels, a
hypodermic fatty layer, diameters of vessels, a sex, age). It is used for examination
of a vascular system and a circulation and for diagnostic.
IR beams in medicine are widely used for examination of a state of a crystalline
lens, an iris and other eye structures at presence of a cataract or opacity of a cornea
(albugo). The able-bodied crystalline lens is transparent for IR beams, and at
inappreciable opacity IR beams are reflected from a crystalline lens and gives the
image in a photo. Mature cataracts are well visible and the structure of a cataract
is clear.
Wide use of night viewing devices enables to use IR beams in military medicine
(it is possible to find wounded peaple on distances of 150-200 m for evacuation and
giving of the first medical aid).
Important role IR beams play in forensic medicine and examination for
determination of distance of a shot, the sizes of a wound, tattooes.
104
Diagnostic of dermal diseases is carried out well: lupus, a skin cancer,
infringements of a skin pigmentation, psoriasis, eczema; it is well visible border of
pathological changes tissue.
IR beams are used in parasitology.
The molecular structure of medical preparations, antibiotics, vitamins,
hormones is studied with help of an IR spectroscopy. Moleculas have the
characteristic IR spectrums, on which it is possible to determine presence of particular
molecular bonds. A set of energy levels (oscillatory and rotary) corresponds to each
interatomic bond; the nuclear environment influences on which precise energy values
also. These levels and the relevant nuclear groups are determined by the reference
lines IR of a spectrum.
One of the first expedients of reception of a thermal pattern of a body surface
was use of liquid crystal films, in which composition there were cholesteric
mesomorphous bodies (liquid crystals), sensing in different temperature ranges. The
color of the liquid-crystal indicators depends on their temperature, i.e. the temperature
of the area on the body where they are placed.A film, sensing in the necessary range,
imposed on a zone subject to examine, and on a film the distribution pattern of heat on
a skin showed.
Thermography
It is method of registration of thermal irradiation of a body. The thermal radiation
emitted by the human body can be measured with special infrared sensors (the main
transduction elements). Infrared camera consists of IR optics, sensor panel, cooler,
amplifying circuit, monitor and computing system. Sensors convert the infrared radiation
emitted by the surface of the skin to electrical voltage values proportional to the
measured temperatures. IR beams coming on panel with IR sensores, cooled by liquid
nitrogen usually, call photoeffect, and electric current amplified in next amplifying circuit,
is used for creation of thermogram (heats pattern). Various voltage values can be
displayed on a monitor by means of a specific software using different colours, from
blue to red.
Medical radio thermal diagnostics is thermography using radio band close to IR.
These waves penetrate from deep layers of body, as IR radiates from skin surface as it
is absorbed easyly in passing from deep zones. Combination of IR and radio
thermography with different wave ranges allows to obtain detailed picture of
temperature distribution inside the body.
Different types and models of infrared cameras exist on the market. Most of them
are used for technical applications such as: night time monitoring, fire fighting devices
etc., which require different spectral bands and sensitivity.
Application of a thermography in clinical medicine
Thermographic examinations widely include into medical practice with the
purpose of reception of the additional data for diagnostic of different diseases.
Such devices have names as thermograph, thermovision camera, infrared
scanner, temperature control unit.
105
Oncological diseases. Development of tumours is accompanied very
frequently by occurrence on a heat zone of a thermogram. However the thermal
picture of tumours is influenced with many factors; thermo-negative tumours are
discovered also.
Thermographic diagnostic of a mammary gland cancer in the best designed. A
focal hyperthermia refers to its basic criteria, when a hot spot is found in a field of
one mammary gland, which (spot) sizes can change from several millimetres up to
2–3 quadrants (a quadrant – a quarter of mammary gland). Thus the opposite
mammary gland remains more cold. The warming of all mammary gland with
intensified light emission of a vascular grid is frequently observed; a hot spots are
detected in the locations of the lymph nodes involved in an inflammation process,
more often - axillary, subclavicular and parasternal.
Thermographic differential diagnostic of a mammalian cancer from a noncancerous growths and hormonal mastopathy is not so reliable, but it allows to
estimate safety and promptly intensity of pathological process and its abundance, to
differentiate states, which require urgent interfering, to determine the affected
organs, thus potentially dangerous manipulations are expelled.
Diseases of cardiovascular system. Disturbed blood supply of the limbs
changes their temperature and, hence, the pattern of thermal radiation. Thermography
it is used in a complex with other research techniques of blood vessels. At
patients with an obliterating atherosclerosis and endarteritis on heats pattern
caloric radiation of the knocked finiteness is reduced, it «thermal amputation» is
observed. The ischemic infringements is more, the more a temperature gradient
between big toe and of a foot and a medial third of hip, which can reach 8°С.
Such examination is very important in survey of patients with a diabetes. It
is very important for early detection of microangiopathies, for example, in close
relatives of patients that promote duly preventive prophylaxis.
Thermography enables to watch a healthy state after a heart attack. At it state
early stage in a heart projection the hypothermic zone with precise temperature
drop is observed.
Diseases of a respiratory organs. Hyperthermia zone appears in 70-80% of
patients on an initial stage of an acute pneumonia on the lesion side. Thermal
asymmetry attains 1–3°С. Thermographic changes typical for an acute inflammation,
are observed at third of patients, in which the pneumonia is not detected during a Xray inspection.
106
Diseases of digestion orhans. Thermography gives the valuable information
at diagnostic of different forms of a pancreatitis, a hepatite and other
inflammations of abdominal cavity organs. It enables to differentiate affected
organs, for example, inflammations of uterine appendages of a uterus from
appendicitis.
Self-control material:
B. Test tasks (α=ІІ):
1) What phenomena influence temperature of a human skin?
a) Boiling
b) Transpiration
c) Temperature of air
d) Radiation
e) A body temperature
f) Ventilation
g) Clothes
3) What itself represents a liquid crystal, which use in heat-indicating diagnostic?
a) Crystals of glass compounds
b) Crystals of elastic polymeric compounds
c) Crystals of metals compounds
d) Crystals of cholesteric polymeric compound
4) What does the heat-indicating film contain?
a) acetylsalicylic acid
b) Polyethylene
c) Lavsan
d) Catran
e) Liquid crystal
5) What are basic elements of the Thermograph?
a) A radio receiver
b) A television receiver
c) The refrigerating block
d) The heat receiver
e) The transformer of thermal signals in electrical.
6) What is basic feature of the thermograph?
a) Receives electrical waves in length of 9-23 m.
b) Receives electrical waves in length 9-23 sm.
c) Receives electrical waves in length 9-23 microns.
d) Receives electrical waves in length of 9-23 mm.
The subject of the research work.
To prepare a report on the subject «Thermography in stomatology and general
therapy».
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – L.D.Korovina. Biophysics with beginnings of
mathematical analysis and statistics. Extended course of lectures. –Vol.2. Basis
of thermodynamics. Biomembranes. Electricity and magnetism. –Poltava, 2014.
107
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. – Poltava,
2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
─ http://www.pnas.org/cgi/reprint/100/19/10722
─ http://www.meditherm.com/therm_page1.htm
108
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 7
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Optical methods. It use in medicine and biology.
Interaction of light with substance. Luxmetry. Basic
quantities of lighting engineering.
1
medical, stomatological
Poltava – 2016
109
The topic significance:
At a light absorption atoms and the molecules of substance gain padding energy
and transfer in an excited state. On occasion it can cause rising of their chemical
reactivity and, in particular, ability to enter in chemical changes, which do not descend
at their usual state. Such atoms and molecules are named activated. The activation of
molecules is featured by the equation A + hν = A*, where A is molecule in a ground
state, hν – photon absorbed by a molecule A, and A* – activated molecule. The basic
law of photochemical reaction:
The quantity of the reacted substance is directly proportional to quantity of an
absorbed energy of radiation.
At interaction of light with substance, at enough major energy of a photon
exceeding a work function of an electron descends either electron emission, or change
of conductivity of substance. Thus there is a dismissal of electrons from atoms of
substance or translates electrons in a state of conduction, i.e. in a state of a photoeffect.
Specific targets:
To carry out examination of dependence of illuminating intensity from distance of
a photoelectric cell from a light source.
To construct the diagram of this dependence.
To acquire concepts: photoeffect, photoemission, photoelectric work function of
an electron, photoelectric cells, photochemical reaction, photobiological reaction.(α=II )
To know Einstein's equation, equation of brightness calculation by the
parameters light source intensity, distance to the surface, incident angle (α=II).
To seize technique of experiment on determination of the brightness (luxmetry
methods) (α=II).
To be able to determine brightness with the help of a luxmeter (α=III).
To seize habits of work with optical bench.
To determine illuminating intensity on working place.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing
To know basic concepts of optics and physical chemistry:
disciplines):
light, wave, light absorption, electron–light interaction,
physics, chemistry, biology
molecule excitation
The subsequent disciplines:
To give definitions of concepts: photoeffect, photoemission,
Biochemistry;
photoelectric work function of an electron, photoelectric
Pharmacology;
cells, photochemical reaction, photobiological reaction.
Normal physiology
To give definitions of energy of radiation, radiant flux,
emittance, exitance, light intensity, light flux, illuminating
intensity, luminosity, brightness.
To know : Diurnal rhythms. Light-linked season rythms.
Concept of molecule excitation as physical and chemical
reactions beginning.
To formulate laws: Einstein's equation, equation of
brightness calculation.
To explain photoelectic cell principle of operation.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Photoeffect
Group of phenomena appearing as a result of interaction of
light with substance, at which there is or emission of electrons,
110
Extrinsic photoeffect
Intrinsic
photoemissive effect
Photoelectric work
function of an
electron
Photoelectric cell
either change of conductivity of substance or originating of an
electromotive force
Emission of electrons owing to interaction of light with
substance
Increase of conductivity of substance or originating of an
electromotive force owing to interaction of light with substance
The quantity of augmentation of an electron kinetic energy due
to photon absorption
Element using the extrinsic photoemissive effect observed in
metals for for photometric needs
Photochemical
The elementary photochemical reaction can be connected or to
reaction
losses of an electron by a molecule, or with its acquisition, or
with destruction of molecules due to light quantum absorption
(Photoionization, Photoreduction and photooxidation,
Photodissociation, Photoisomerization, Photodimerization).
Photobiological
The processes descending in biological systems at absorption
reaction
of a radiant energy: 1) photosynthesis, 2) regulation processes:
phototaxis, phototropism and photoperiodism of plants and 3)
infringement and destruction processes
Radiant flux
It is energy W irradiated during the time t
Light flux
Φ: It is product of light intensity of light source I on space angle
ω
Exitance (luminosity) R: It is ratio of luminous flux Φ emitted by luminescent surface
to area S of it surface
Emittance
Surface density of luminous flux φ is ratio of luminous flux Φ to
area of cross-section S through that this flux pass is used for
measuring of characteristic of emitting surfaces
Brightness
Surface density of luminous flux φ is ratio of luminous flux Φ to
area of cross-section S through that this flux pass is used for
measuring of characteristic of illuminated surfaces
Diurnal rhythm
Changes of biological organisms activity during day and night
(photosynthesis, hormon levels, another biochemical reactions
and total activity changes in microorganisms, plants, and
animals).
Theoretical questions to class:
1.
What is light [luminous] flux? (=ІІ)
2.
What is one steradian angle? (=ІІ)
3.
What units are used for luminous flux measurement? (=ІІ)
4.
What is named as light intensity? (=ІІ)
5.
What units are used for light intensity measurement? (=ІІ)
6.
What light intensity is 1 cd? (=ІІ)
7.
What is named as illuminance [illumination intensity]? (=ІІ)
8.
On what illumination intensity depends? (=ІІ)
9.
On what formula illumination intensity is measured? (=ІІ)
10.
How illumination intensity depends on distance from a light source? (=ІІ)
11.
How illumination intensity depends on angle of incidence of a light? (=ІІ)
12.
In what unities illumination intensity is measured? (=ІІ)
13.
What is lux? (=ІІ)
14.
What is termed as luminosity? (=ІІ)
15.
What is difference between illuminance and luminosity? (=ІІ)
111
16.
What is termed as brightness unit stilb? (=ІІ)
17.
What is termed as brightness unit nit? (=ІІ)
18.
In what the appearance inner and extrinsic photoemissive effect consists? (=ІІ)
19.
Formulate the laws of a photoeffect. (=ІІ)
20.
Note the Einstein's equation for a photoeffect. (=ІІ)
21.
Formulate definitions and specify units of the basic photometric quantities: a
luminous flux, force of light, illuminating intensity. (=ІІ)
22.
Tell about use of photoelectric cells in scientific and medical examinations and
about their practical application. (=ІІ)
23.
How the photoresistance varies depending on a luminous flux? (=ІІ)
24.
What is a photoelectric work function of an electron and from what it depends?
(=ІІ)
25.
What is thermal electron emission?
26.
What is light diffraction? (=ІІ)
27.
What phenomenon is termed as photoeffect? (=ІІ)
28.
What kinds of a photoeffect exist?? (=ІІ)
29.
What is difference between inner and extrinsic photoeffect? (=ІІ)
30.
How action of light on the chemical substances speaks? (=ІІ)
31.
How biological action of light on an organism speaks? (=ІІ)
32.
What is purpose of photoelement using in medicine? (=ІІ)
33.
Why it is necessary to measure illumination intensity in medical practice? (=ІІ)
Practice work executed at class.
Professional algorithms (instructions, reference cards) concerning
mastering habits and skills:
Devices: a luxmeter, optical bench, ruler.
№
Task
Sequence of performance
Remarks, warnings
concerning selfchecking
1 Determine
Carry out in such sequence:
Remember about
illuminating
1. Establish the device.
correct position of
intensity on a
2. To measure with the help of a luxmeter the device
working table
illuminating intensity on various distances from a sensitive element
with the help of light source (window-sill, blackboard,
in relation to
a luxmeter.
different points of a working room).
direction of light
3. Light up a room maximally with the lamps.
incidence.
2 Measure with
Familiarize with optical bench and luxmeter.
To give attention
the help of a
Allocate sensitive photoelectric cell on 10 cm on accuracy work
luxmeter
distance from the lamp on the one level with lamp with optic bench.
illuminating
(on the axis of the box output opening).
intensity on
Choose 300 lux sensitive range.
When output data
various
Readout data. Put into the table observed data will be in the short
distances from
and results of evaluations.
range (30 lux),
a light source
Move photoelectric cell on the next position. change luxmeter
Repeat measurement.
sensitive range.
Data chart
r, cm 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Е, lux
112
4) Construct the diagram of dependence of illuminating intensity from distance
between a photoelectric cell and light source E = f (r).
E, lux
r, cm
5) On the basis of these measurement to make a deduction.
The content of the topic:
Thermal electron emission [thermionic emission, Edison effect, Richardson effect,
filament emission, термоэлектронная эмиссия] is emission of the electrons by heated
metals. Electron can leave metal if its full energy W is more then work function A. This
appearance becomes intensive at metal temperatures near hundreds Kelvin degrees.
It’s used in work of electronic vacuum tubes. Illumination influences on electron energy
too.
Photoeffect is term of group of appearances appearing as a result of interaction of
light with substance, at which there is or emission of electrons (extrinsic photoemissive
effect), either change of conductivity of substance or originating of an electromotive
force (inner [or intrinsic] photoemissive effect).
The extrinsic photoemissive effect can be observed in metals. In these problems
the Russian scientist О. G. Stoletov was engaged which has paid attention to practical
use of photoelectric cells for photometric needs. The extrinsic photoemissive effect
arises at irradiating metal, when the photon is absorbed with a conduction electron; that
gives augmentation of a kinetic energy of an electron. If the quantity of this energy
exceeds a photoelectric work function of an electron, the electron leaves from metal.
This process energy is featured by the Einstein's equation:
hν =A+mv2/2,
Where hν – energy of a photon, A – photoelectric work function of an electron,
2
mv /2 – kinetic energy of the emitting electron.
The analysis of this equation testifies that electrons move independently from each
other in metal, and consequently the change of one electron energy at uptake of a
photon does not give change of energy of other electrons, i.e. the photon interacts only
with one electron.
On the basis of experimental data three laws of a photoeffect were ascertained:
1) The number of photoelectrons which are pulled out from a surface of metal for a
time unit is proportional to a luminous flux incident on metal, at an invariable spectral
distribution.
2) The maximal initial kinetic energy of photoelectrons is determined by frequency
of an incident light and does not depend on its intensity.
3) For each metal there is a red photoelectric threshold, i.e. maximal wavelength
λ0, at which the photoeffect is even possible.
The magnitude of a photoeffect depends on a chemical nature of metal and state
of its surface. From the Einstein's equation it follows, that the electron can exceed the
bounds of metal, if the energy, imparted to it, is not less a photoelectric work function,
i.e. hν0≥A. As frequency ν0=с/ λ0, that λ0=hc/A.
The appearance of a photoeffect has gained wide use in various branches of a
science and technique for account of its basic property to transmute light energy into
113
electrical. The devices, which transmute light energy into electrical, are termed as
photoelectric cells.
The photoelectric cells are widely utilized in devices for measuring and recording
of luminous fluxes (various relays, signal system, accounting automatic devices,
systems of protection near machine tools, television, sound cinema, phototelegraph,
electrophotocolorimeters, luxmeters etc.)
Illuminating intensity is measured by a luxmeter, which represents a photometer
used for determining of a degree both artificial and natural illuminating intensity. Or else,
the receiver of light energy in luxmeters is served by photoelectric cells presenting
photoelectric sensor. The division of optics occupied with problems of an emission,
diffusion and absorption of light, and as irradiating of various items, is termed as a
photometry.
Light spreading in space has certain energy. If on the given surface the luminous
flux falls, it means, that the given surface every second gains some of a radiant energy.
Energy of radiation W is measured in J (joule, watt-second) as some other energy.
Volume density of irradiation energy is ratio of energy of radiation W to volume
V in which this energy contains, and unit is J/m3.
Radiant flux is energy W irradiated during the time t, and unit is J/s. Φ = W/t;
1 J/s = 1 W (watt). It is equivalent to mechanical power.
Surface density of luminous flux φ is ratio of luminous flux Φ to area of crosssection S through that this flux pass. φ = Φ/S. Unit is W/m2.
This unit is used for measuring of emittance [radiant exitance, radiancy] and
energetic brightness [energetic illuminance, energetic illumination].
Emittance is used as characteristic of emitting surfaces, their emissivity [emittance,
transmissibility], brightness – characteristic of illuminated surfaces.
Light intensity [luminous intensity, intensity, illumination power, light power,
luminous power]. It is one of basic ideas and mark as I. Unit of light intensity is one of 7
main units of SI – International Unit System. Candela (cd) is equal to light intensity
irradiated from surface 1/600 000 m2 of complete radiator at platinum solidification
temperature of radiator at pressure 101 325 Pa and perpendicular direction. (Complete
radiator is meant as an absolute black body).
Measuring of light values is based on physiological action of light and therefore in
considerable part it has subjective character. Radiation with λ=556 nm makes most
action on eye. Thus during measuring of light average sensitivity of many healthy
A
B
Fig.1. Illumination of surface from the luminous point (A); Illumination of
114 and brightness of light source (B).
surface from the of luminous surface
people is used.
Light flux [luminous flux] Φ is product of light intensity of light source I on space
angle ω [solid angle, spatial angle]: Φ = Iω. Unit is lumen (lm); 1 lm = 1cd·sr, where sr
is steradian – unit of space angle.
The complete luminous flux of a light source names a luminous flux radiated by
this light source on all directions.
The illuminating intensity [brightness, illuminance, illumination] (Е) is determined
by a luminous flux come on unit of a surface. As unit of illuminating intensity 1 lux is
accepted illuminating intensity framed by an evenly distributed luminous flux 1 lumen on
the surface 1m2, normally posed to a luminous flux:
E=Φ/S.
Unit is lux (lx); 1 lx = 1 lm/m2.
Except for unit of illuminating intensity a lux, one more unit – phot (ph) is
accepted. 1 Phot is illuminating intensity created by an evenly distributed luminous flux
1 lm on a surface 1 sm2, normally posed to a luminous flux: 1phot = 10–4 lux.
Exitance [luminous exitance, luminosity] R – is ratio of luminous flux Φ emitted
by luminescent surface to area S of it surface: R = Φ/S.
Unit of exitance is lux (as unit of illuminating intensity).
Concept of exitance. It can be distinguished luminosity or brightness of active
radiator and brightness of surface with reflectance. The surface brightness terms value
gauged by force of light irradiated from a unit area of this surface in normal to the
surface a direction; i.e. the luminosity is quantity, characterised not only radiating light
surfaces, but also surfaces reflecting it (for example, illuminated by a light source).
B = I/S.
If the light power is equal to 1 candela (cd), and the area of radiating surface 1 m2,
its luminosity is equal to unit named nit: В = 1cd/m2. In Russia this name don’t used
today.
Other unit of luminosity – 1 stilb. 1 stilb = 1 cd/cm2 = 104 cd/m2 = 104 nit.
Brightness [brilliance, luminance, intensity, luminosity, luma] Bφ of luminescent
surface into certain direction φ is ratio of light intensity I in this direction to area S of
luminescent surface projection on the plane which is perpendicular to given direction:
Bφ = I/(Scosφ).
Unit is candela per square meter – 1 cd/m2.
Other determination is following. Thus, the illuminating intensity [brightness,
illuminance, illumination] is directly proportional to force of light source and cosine of an
angle of incidence of rays and is inversely proportional to a square of distance from a
light source up to a surface element lighted by it.
The illuminating intensity from a point source of light can be determined by the
formula: Е = I • cos α/r2 (see fig.1,A).
Where I – force of light of a point source of light in the given direction in unit of a
space angle; r – distance from a light source to the illuminating area; cos α – cosine
angle, under which the light rays fall. Unit is candela per square meter too.
Self-control material:
Test tasks to be done (=ІІ):
1. Under what formula illumination intensity calculates?
A) Е=Іr2 /cos 
B) Е=Іcos  / r2
C) Е=Іsin  / r2
D) Е=Іr2  cos 
2) Under what formula brightness calculates?
A) В=ІS
115
B) В=S/Іsin
C) В=Іcos/S
D) В=І/Scos
E) В=І/Ssin
3) Under what formula photon energy calculates (hν – energy of a photon, A –
photoelectric work function of an electron, m – emitting electron mass, v – emitting
electron velocity)?
A) hν = A mv2/2
B) hν = A + mv2/2
C) hν = A + 2m/v2
D) hν = A + 2v2/m
E) hν = A – 2v2/m
Tasks for self-checking:
A brightness of working surface must be 350 lux. How many lamps with luminous flux
1000 lm must be allocated at the 3 m distance from the working surface to average
brightness correspondence to requirements?
Task 2. Calculate parameters of dependence Е = I • cos α/r2 in conditions of our
experiment.
Materials for after auditorium independent work.
Prepare the abstract on a theme: «Effects of light on the human organism functions.
Diurnal fluctuations of hormon levels and working ability of human organism».
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. –Poltava,
2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
116
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 8
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Elements of quantum mechanics.
Dimensioning of erythrocytes with the help of a
diffraction of a laser radiance.
1
medical, stomatological
Poltava – 2016
117
1.
2.
3.
4.
5.
6.
The topic significance:
The wave nature of light limits image sharpness (or resolving limit). Due to
diffraction it is impossible to resolve a details, which size is less then wave length,
therefore it is essential limit of an optical microscopy opportunity. But, as diffraction
picture is completely determined by characteristics of those objects, which have created
this picture, it can be used for analysis of those characteristics.
Analysis of this picture can give the information, both about size, and about
arrangement of these objects in space. Firstly, it is diffraction using for the small objects
sizes definition, secondary - for the analysis of object structure (for example, X-ray
structure analysis). These methods are widely used in biophysical researches.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
To form the professional experience by reviewing, training and authorizing it;
Study of diffraction of a laser irradiation on monodisperse particles (erytrocites).
Measurement of erytrocite diameter.
To be able to carry out laboratory and experimental work.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing disciplines):
To know concepts: electromagnetic field, wave
physics
spreading, optic appearances – diffraction,
interference, atom energetic levels.
The subsequent disciplines:
To know appearances: atom excitations,
Biochemistry
transmissions between energetic level,
spontaneous and forced irradiation, laser structure
and principle of operation.
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Laser
Device used forced irradiation of light for it amplification
Stimulated emission It is a process happens if a photon is hit to the electron in
an excited state.
Diffraction
Bending of waves around small obstacles and the
spreading of waves passed through small openings.
Theoretical questions to class:
1.
Describe the laser structure. Explain the laser work principle.
2.
The phenomenon of diffraction and it’s meaning.
3.
What is diffraction grating?
4.
The interference phenomenon and it’s meaning.
Practice work executed at class:
Erythrocyte size determining with the lazer irradiation diffraction using.
– to put a glass with erythrocytes in a support;
– to measure distance from a glass with erythrocytes up to the screen L;
– to switch on the laser and achieve precise a picture of diffraction;
– to measure distance from the diffraction picture center (of a zero maximum) up to first
and second minima and first maximum (l1, l2, l3);
– determine radius of erythrocytes corresponds to the formulas:
118
 ,  λ  L  l
for the first minimum: r 
;
l
 ,  λ  L  l 
for the first maximum: r 
;
l
for the second minimum: r  
–
–
–
–
N
1
2
3
,  λ  L  l
.
l
to calculate average value of erythrocyte radius;
to put results into the first row of the table.
to change distance L between the glass and the screen, repeate experiment, fill
next table row.
To calculate total average value of erythrocyte radius
Table
L,m
l1, m
r1, m
l2, m
r2, m
l3, m
r3, m
Average r, m
Make the conclusion.
The contents of the topic:
Installation is optic bench with devices: helium-neon gas laser; blood smear on
object-plate disposed in holder; screen; ruler.
Helium-neon laser is source of radiation with wavelength λ = 632,8·10–9 m.
Diffraction method of small object size measurement has high precision, higher
than microscopic or many others.
Lasers generate electromagnetic waves with set of specific characteristics:
coherence; directionality; monochromaticity; focusability; intensity or irradiance.
Fig.1. Construction scheme of laser.
There are three radiative transitions that are important in semiconductor lasers
and occur between the conduction and valence bands of the material. A schematic
diagram of the transitions is shown on fig.3.
119
Fig.2. Energy transitions of electrons in laser active medium.
In the first process, an electron in the valence band gains energy by absorbing a
photon, exciting it to a higher energy level within the conduction band. The energy
gained by the electron is equal to the energy of the photon.
ħω = E2 – E1.
The spontaneous emission process begins when an electron is in an excited
state in the conduction band. The electron can fall back into the valence band, releasing
the excess energy in the form of a photon with an energy given by ħω.
The transition probability of an excited particle falling into a vacant lower state is
value A21. It describes spontaneous emission rate by way:
Rspon = A21p2(1–p1), where p2 and p1 are the occupation probabilities of the upper
and lower states respectively.
Stimulated emission is a process happens if a photon is hit to the electron in an
excited state. It can cause electron to pass to a lower energy level, releasing a photon
of the same energy. The emitted photon has the same direction and phase as the
incident photon.
When high quantity of medium atoms stay on excited energy level, then
spontaneous radiation of some atom can to involve chain radiation reaction. But only
waves propagated along rod axis can amplify due to mirrors – fully reflecting of one end
and semitransparent on work (radiating) end.
Energetic pumping of medium is realized by electrical discharge (as in heliumneon gas laser), electric current (in semiconductor laser diode), chemical reaction,
flashlamp (as in ruby solid-state laser).
Diffraction manifests itself in the apparent bending of waves around small
obstacles and the spreading of waves passed through small openings.
The first proof that light had wave characteristics was furnished in 1800 by the
experiment on the interference of light from a double slit by Thomas Young (17731825). The experiment is now referred to as Young's double-slit experiment.
Young's double-slit experiment is shown in fig.3. Light from the source passes
through the narrow slit in the first screen and is diffracted. When light from the first slit
reaches the second set of slits, it is again diffracted as if there was a point source at
each of the secondary slits. The waves from each slit now propagate toward the screen
where they interfere, or superimpose, with each other.
Under the Fraunhofer conditions, the light curve of a multiple slit arrangement will
be the interference pattern multiplied by the single slit diffraction envelope. This
assumes that all the slits are identical.
Where the superimposed waves are in phase on the screen, there is constructive
interference and a brightness of image rises.
“In phase” means that difference between the two waves is a whole number of
wavelengths.
120
Fig.3. Young's double-slit experiment.
Hence, the observed distribution of light, that is, bright and dark rings, can be
explained by the processes of diffraction and interference, both wave manifestations of
light.
Fig.4. Diffraction picture of small opening.
A large number of parallel, closely spaced slits is a diffraction grating. The
condition for maximum intensity is the same as that for the double slit or multiple slits,
but with a large number of slits the intensity maximum is very sharp and narrow,
providing the resolution for spectroscopic applications.
If there is a need to separate light of different wavelengths with high resolution,
then a diffraction grating is most often the tool of choice. This "super prism" property of
the diffraction grating leads to application for measuring atomic spectra in both
laboratory instruments and telescopes.
The wave properties of light lead to interference, but certain conditions of
coherence must be met for these interference effects to be readily visible. Thin films the
optical properties of thin films arise from interference and reflection. The basic
conditions for interference depend upon whether the reflections involve 180° phase
changes.
121
A diffraction grating is the tool of choice for separating the colors in incident light.
The condition for maximum intensity is the same as that for a double slit. However
angular separation of the maxima is generally much greater because the slit spacing is
o small for a diffraction grating (fig.3).
In experiment monoshromatic laser beam falls on round particle (erythrocyte) with
radius r, and forms diffraction pattern on screen placed at distance L from particle. At
relative large distance diffracted rays form beams, which are practically parallel.
Diffraction pattern on screen is periodical distribution of brightness in the form of rings –
diffraction maxima and minima (fig.4, 5).
Fig.5. Five slit diffraction. Similar picture will be in case of blood smear.
Conditions of maxima: r·sinφ0 = 0,
r·sinφ2 = 0,81·λ,
r·sinφ4 = 1,33·λ,
Conditions of minima: r·sinφ1 = 0,61·λ,
r·sinφ3 = 1,12·λ,
r·sinφ5 = 1,62·λ,
where φ – angles of ray diffraction, λ – vawe length.
Obtained diffraction pattern of one erythrocyte can be extremely weak an
background of direct undiffracted light. In blood smear large quantity of erythrocytes
multiply diffraction pattern.
At normal falling of rays on blood smear relation of vawe length, slit size between
erythrocytes and angle of rays declination is:
nλ = ds·sinφ,
whence
d = nλ/ s·sinφ.
It gives possibility to calculate diffraction angle by the schematic diffraction pattern
(fig.6.):
nλ  L  l
d
,
l
122
whence
sin φ 
l
L  l
.
Fig. 6.
Determine radius of erythrocytes corresponds to the formulas:
 ,  λ  L  l
for the first minimum: r 
;
l
 ,  λ  L  l 
for the first maximum: r 
;
l
,  λ  L  l
for the second minimum: r  
;
l
,  λ  L  l 
for the second maximum: r 
;
l
,  λ  L  l
for the third minimum: r 
.
l
Self-control material:
B. Test tasks (α=ІІ)
1. What device used in Young's double-slit experiment?
a) diffraction grating;
b) observation slit;
c) double-slit;
d) diffraction cell.
2. When is maximum of brightness observed after diffraction of laser
irradiation on the thin layer of small objects?
a) in the center of screen;
b) in the first maximum ring;
c) in the second maximum ring.
3. What phenomenon observed in Young's double-slit experiment?
a) reflection;
b) refraction;
c) diffraction;
d) interference.
4. What is the difference between coherent and incoherent light?
a) coherent light have only one frequency waves;
b) incoherent light have only one frequency waves;
c) coherent light have coincident phases of waves;
d) incoherent light have coincident phases of waves;
e) coherent light have less biological effect than incoherent light at same power.
123
5. Does a fluorescent light lamp produce coherent or incoherent light?
a) yes;
b) only temporally coherent;
c) only spatially coherent;
d) no.
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. –Poltava, 2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for students,
physicians and researchers. Nico A.M. Schellart. – Department of Biomedical
Engineering and Physics Academic Medical Center University of Amsterdam.–
Amsterdam.– 2009 (electronic book).
─ Roland Glaser. Biophysics: An Introduction.– 2010.
─ Philip Nelson. Biological Physics (Updated Edition).– 2007.
─ Paul Davidovits. Physics in Biology and Medicine, Third Edition (Complementary
Science). – 2007.
─ Bengt Nölting. Methods in Modern Biophysics.– 2009.
The subject of the research work.
To prepare a report on the subject «Modern lasers in stomatology, surgery and general
therapy».
124
Ministry of Health of Ukraine
Higher State Educational Establishment
“Ukrainian Medical Stomatological Academy”
“It is approved”
on meeting of department of
medical informatics, medical biophysics
and bases of vital activity safety
Senior-lecturer ________O.V.Silkova
«29» august 2016
Methodical Instructions
For the 1st year students’ self-preparation work
(at home and at the classroom)
in studying medical and biological physics
Subject matter
Module № 2
Meaningful module № 9
Topic
Year
Faculty
Medical and biological physics
Bases of biological physics
Radiation physics. Bases of a dosimetry.
Radioactivity. Kinds of radioactivity, them
characteristics. A dosimetry
1
medical,stomatological
Poltava – 2016
125
The topic significance:
Radioactivity is common appearance of outer word, as natural radiation is
present in form cosmic rays and Earth irradiation. But it gains in importance at XX
century with use of artificial sources of ionizing radiation. In modern life it present both
as technological radiation, and as medical diagnostical and treatment methods.
Sometimes any doctor can face with a problem of radiation-exposed patient.
Specific targets:
To have general knowledge of the topic studied;
To understand, to remember and to use the knowledge received;
To form the professional experience by reviewing, training and authorizing it;
To be able to carry out laboratory and experimental work.
Basic knowledge, experience, skills necessary for studying the topic in
connection with other subjects:
Disciplines
Obtainable skills
Previous (providing disciplines): physics,
To know concepts: ionizing radiation,
biology
radioactivity, radiactive decay, isotopes.
The subsequent disciplines: Normal
To know concepts and describe ideas:
physiology, patological physiology
types of decay, radiolysis of water,
photoeffect,
incoherent
scattering,
annihilation,
To know the Bouguer law.
To describe basic symptom-complexes o f
infringement of functions of an
organism by ionizing irradiation
Materials for the before-class self-preparation work:
List of main term, parameters, characteristics, which student have to learn at
preparation to class:
Term
Definition
Half-life period
The half-life period of the substance is the time during which
the amount of radioactive atoms decreases two-fold.
lonization braking
It happens when α- and β–-particles electrically interact with
the electron shells of the atoms and lose their energy on
ionizing atoms.
Annihilation reaction
The reaction of interaction of positrons and electrons with
formation of 2 γ-quantums.
Penetrability of
The capability of radiation to penetrate through the matter is
radiation
known as their penetrating capacity (penetrating power).
Radiolysis of water
Formation of ions and radicals from water.
Radiotoxins
Unsaturated fatty acids, amino acids and phenolums oxidazed
during irradiation forme lipid and quinones radiotoxins, which
depress synthesis of nucleic acids, react on DNA molecule as
chemical mutagen, vary activity of enzymes, and react with
lipid-albuminous endocellular membranes.
Maximum permissible
dose
Maximum permissible
dose for professional
exposure\
The maximum permissible dose is the maximum value of an
individual annual equivalent dose, which, at uniform exposure
during 50 years, shall have no detrimental effect on man's
health.
The maximum permissible annual equivalent dose for
professional exposure is equal to 5 rem.
126
Ionizing radiation
detector
Dosimeter
Ionizing radiation detectors are intended for registering
radiation and measuring some of their characteristics (e.g.,
energy and velocity of particles, the ratio of their charge to
mass, and others).
Dosimeters are devices for measuring doses of ionizing
radiation, or values related to doses.
Theoretical questions to class:
1. What is spontaneous decay?
2. Describe types of spontaneous decay.
3. What substances can be radioactive?
4. Describe and explain the law of radioactive decay.
5. Mechanism of ionizing irradiation interaction with substances.
6. Photoeffect, incoherent scattering (Compton effect) and formation of electronpositron pairs.
7. Characterize penetrability of radiation. The Bouguer law.
8. Describe radiolysis of water.
9. What are radiotoxins?
10. Infringement of vital activity of cells by ionizing irradiation.
11. Basic symptom-complexes of infringement of functions of an organism
by ionizing irradiation.
12. Radiation sickness.
13. Absorbed dose, Equivalent dose, Effective equivalent dose, Collective effective
equivalent dose, Complete collective effective equivalent dose.
14. Units of dosimetry: Gray, rad, coulomb per kilogram, roentgen, grey per second.
15. Relative biological effectiveness.
16. Units of dosimetry: rem , sievert, person-rem.
17. Maximum permissible dose.
18. Effective equivalent dose.
19. Collective effective equivalent dose.
20. Expected collective effective equivalent dose.
21. Dose rate.
22. Detectors of ionizing radiation: track detectors (Wilson chamber, the bubble
chamber, spark chamber, thick-layer photo plates), counters (proportional
counter, the Geiger counter) and integral devices.
23. Dosimeters: ionization, luminescent, semiconductor and photo dosimeters.
Contens of the topic.
Nuclear decay
Radioactivity most often is result of a spontaneous decay of unstable nuclei followed by
emission of other nuclei or elementary particles. It is main source of corpuscular ionizing
radiation. Corpuscular radiations are gained artificial with the help of particles
accelerators.
Nucleuses of atoms of the same element always contain the same number of
protons, but the number of neutrons in them can be varied. The atoms having
nucleus with identical number of protons, but with different quantity of neutrons, are
termed as isotopes of the given element. Neutrons are electrically neutral particles
with mass, the close to 1 u (nuclear unity or atomic mass unit).
For their discrimination to an element sign there are assigned the number peer to
the total of all particles in a nucleus of the given isotope. So, uranium-238 (U238)
contains 92 protons and 146 neutrons; in uranium-235 (U235) too 92 protons, but 143
neutrons.
127
Some isotopes (nuclides) are stable, i.e. in absence of exterior action never undergo
any transmutations.
The majority of nuclides are unstable; they are capable to be transmuted
spontaneously into other nuclides, undergoing a nuclear decay. The moment of such
decay is determined by stochastic laws.
γ-Quantums are emitted by excited nuclear nucleus during nuclear reactions. A nucleus
as well as the atom, represents a quantum-mechanical system with a discrete set of
energy levels. At transition of a nucleus from one energy state into another γ-quantum is
emitted; its energy is peer to a difference of energy levels of a nucleus before and after
transmutation.
Most often, α-decay and β-decay of nuclei are observed. At α-decay, α-particle is
emitted. α-Particle is a helium atom nucleus 2He with mass 4,003 and charge equal 2
units. Atom formed in result of α-decay has the mass number (A) of which is four units
less than that of the mother nucleus, the atomic number (Z) being two times less than
that of the mother nucleus.
β-Particle is name of fast moving electrons and positrons emitted as result of intrinsic
nuclear conversions. Three types of β-decay are distinguished: electron decay (β–decay), positron decay (β+-decay) and the so-called e-capture. At β-decay of a nuclear
nucleus the electron (or a positron) and antineutrino (or, accordingly, neutrino) is
emitted. Thus the atom is transmuted into an isotope of a previous element when the
positron is emitted, and in an isotope of the following in periodic system of elements,
when an electron is emitted.
During e-capture the atom nucleus captures one of the inner electrons of this atom. In
so doing, a new nucleus is formed, with an atomic number a unit less than that of the
mother nucleus. The previous mass number is retained and a neutrino is emitted.
At all kinds of β-decay there may occur X-radiation or γ-radiation.
Protons (hydrogen nuclei with mass ≈1), deuterons (deuterium nuclei with mass ≈2) can
be emitted from nuclei in time of some nuclear reaction, for example, at alpha-particle
bombardment of some heavy nuclei.
The properties of elementary particles which are most relevant for their interactions with
matter are the type of particle and its kinetic energy. Energy Е of any kind particles of
corpuscular radiation is determined by their rate of a movement:
mv 
E
, where т — particle mass; v — its velocity.

The proton has a rest mass of 1.008 atomic mass units (au). One electronic charge unit
(e) equals 1.602 x 10-19 coulombs (C). The electron-volt (eV) unit of energy is used
extensively in radiation science: 1 eV = 1.602 x 10-19 joules (J).
Law of radioactive decay. Radioactive substance activity
During radioactive decay of a substance, the number of its atoms decreases with time.
The dependence of the number (N) of non-decayed atoms on time (t) during radioactive
decay is known as the law of radioactive decay. This dependence has the form:
N = N0•e–λt, where N0 is the initial (at t=0) number of the atoms of the radioactive
substance; it is a decay constant for the given substance. In some cases the
radioactive decay law is written as follows:
N  N  

t
T ,
where T is the half-life period of the substance. The half-life period is the time during
which the amount of radioactive atoms decreases two-fold. It can be shown that
T = ln2/λ ≈ 0,7/λ.
The intensity of ionizing radiation formed during radioactive decay is in direct proportion
to the number of atoms disintegrating per unit time. To characterize the rate of decay of
128
a radioactive substance the activity (A) is used. The activity of a substance is equal to
A = –dN/dt.
From the law of radioactive decay it follows that the activity of a substance changes with
time by the relation: A  λN  λN  e  λt
The unit of the radioactive substance activity is Becquerel (Bq). Activity of material
equals one Bq, if one atom of substance decays per a second. In practice, Also curie
(Ci) and rutherford (Rd) are used as off-system units.
1 Ci = 3.7·1010 Bq; 1 Rd =1 MBq.
Interaction of ionizing radiation with a material
The ionizing radiation produces excitation and ionization of atoms, i.e. transmitting of
electrons of atom on higher energy levels.
Excitation of atom descends, if it absorbs energy no more than 10 eV, which is equaled
about binding energies of an electron with a nucleus. The electron thus remains in
borders of atom. At reverse transition of electrons from excited levels on basic the
earlier absorbed energy is radiated as quantums of visual, ultraviolet or X-ray radiation.
Besides excited atoms can to enter chemical interaction.
If the atom absorbs energy of more binding energy of an electron with a nucleus the
electron leaves borders of atom (molecule) – there is ionization. Atoms and the
molecules which have lost electrons, become positively ionized atoms. Released
electrons, being associated to neutral atoms and molecules, form negatively ionized
atoms. Besides electrons, breaking out from atoms, can have major energy, and then
they are capable to ionize atoms and molecules and to originate secondary electrons.
The mechanisms of ionization are different for different kinds of ionizing radiation.
lonization braking is the basic ionizing mechanism for α- and β–-radiation. These
charge particles electrically interact with the electron shells of the atoms and lose their
energy on ionizing atoms.
The β+-particles (positron) interact with the electrons of atoms. The reaction of
interaction of positrons and electrons is known as the annihilation reaction. During the
annihilation reaction the positron and electron disappear to be replaced with several
(usually two) γ-photons. Due to this reaction the atom is modified to an ion.
During ionization deceleration the β–-particles can emit X-ray radiation. It can also ionize
atoms of substance.
There are three basic mechanisms of γ-radiation interaction with a substance:
photoeffect, incoherent scattering (Compton effect) and formation of electronpositron pairs. The first two mechanisms are considered early. Formation of electronpositron pairs is observed only at sufficiently high energies of γ-quanta (more than 1,2
MeV). In this case the γ-photon disappears to be replaced by an electron and positron.
These charge particles can ionize neutral atoms.
More often than other mechanisms, photoeffect is observed at relatively small energies
of γ-quanta; incoherent scattering prevails at medium energies, and formation of
electron-positron pairs occurs at high energies of γ-photons.
In addition to the primary mechanisms considered above, interaction of γ-radiation with
a substance displays secondary ionization mechanisms (as there are displayed at
interaction with other kinds of ionizing radiation too).
At photoeffect the dislodged electron can attach to another atom to form a negative ion.
The vacancy lower level can be occupied by an upper-level electron to form an Xradiation photon, which also produces ionization.
At incoherent scattering the Compton electrons can ionize a substance due to the
ionization braking mechanism or at abrupt braking they can generate X-radiation.
129
When electron-positron pairs are formed, the emerging electrons can have a sufficiently
high energy and ionize a substance due to the same mechanisms that Compton
electrons.
Photonuclear reactions are radioactive transformations of atom nuclei after they
have absorbed γ-photons. Neutrons by themselves do not cause ionization of a
substance, but in interacting with the nuclei of atoms they generate ionized radiation.
Interaction of neutrons with nuclei causes either scattering of neutrons or their capture
by the nuclei.
Neutrons by themselves do not cause substance ionization, but in interacting with the
nuclei of atoms they generate ionized radiation. Interaction of neutrons with nuclei
causes either scattering of neutrons or their capture by the nuclei.
During scattering part of the neutron's kinetic energy is transferred to the nucleus. Light
nuclei receive a high velocity with sufficient kinetic energy for ionizing. They are termed
Compton nuclei. When capturing a neutron the nucleus goes to an excited state, which
is often an unstable one. In this case it can be observed nuclear fission, though
reactions with emission of protons or α-particles can also occur.
Penetrability of radiation
In passing through a material, the γ-radiation flux can attenuate. The Bouguer
law describes the attenuation of the flux of a monochromatic γ-radiation (similar to Xrays): Φ = Φ0e–μt,
where μ can be presented as μ = μph + μс + μр,
where μph, μc and μp are the components of the total absorption coefficient due
to photoeffect, the Compton effect and formation of electron-positron pairs respectively.
Passage through the substance a charged particle flow is characterized by linear
ionization density, linear braking capacity, and mean free path.
Linear ionization density (i) is the ratio of the number of ions of one sign (n),
formed by the particle in travelling over path l, to the length of this path. Therefore,
linear braking capacity (S) is the ratio of energy (E), lost by the particle in travelling over
path l, to the length of this path
i
dn
.
dl
Linear braking capacity (S) is the ratio of energy (E), lost by the particle in
travelling over path l, to the length of this path
S
dR
.
dl
The mean free path is the mean distance passed by the particle in a substance
until its velocity decreases to the particle's thermal velocity.
The capability of radiation to penetrate through the matter is known as their
penetrating capacity (penetrability, penetrating power). Neutron, γ- and X-radiation
possess a high penetrating capacity. Charged particles possess a significantly less
penetrating capacity. Usually the greater the penetrating capacity of the radiation the
less is its ionizing capacity, and conversely.
α-Radiation has low penetrating ability, being impeded, for example, a leaf of a
paper, and practically is not capable to penetrate through the external skin layer forming
by mortified cells. Therefore it does not represent danger until the radioactive materials
which are emitting α-particles, it will not get inside of an organism through an unclosed
wound, with nutrition or with inhaled air; then they become extremely dangerous.
β-Radiation transits in a tissue of an organism on depth of 1–2 centimeter.
Penetrability of γ-radiations is very great: only thick lead or concrete plate can detain it.
130
Biophysical bases of interaction of an ionizing radiation with biological tissues.
Direct action of radiation
At activity of the ionizing radiation in organisms initial physicochemical processes
which consist in formation of chemically high-active compounds – excited molecules,
ions, radicals, and peroxides proceed.
Being absorbed by a macromolecule, energy of ionizing radiation can migrate on
a molecule, being implemented in most weak spots. Results are ionization, excitation, a
disruptive of the least strong bonds, a separation of the radicals termed as free.
Initial target can become high-molecular compounds (proteins, lipids, enzymes,
nucleic acids, molecules of the composite proteins – nucleoprotein complexes,
lipoproteins). If DNA molecule appears the target the genetic code can be broken.
As the alive organism contains a plenty of water (60-90 %) the greatest value in
development of a radiation injury has a radiolysis of water, i.e. formation of ions and
radicals from water. Main products of a radiolysis are: Н2О*, ОH•, H•, Н3О+, e–, Н2О–,
ОН–.
At the presence of oxygen it is probable formation of hydroperoxide and peroxide
of hydrogen НО2•, Н2О2, and also atomic oxygen О.
Energy of radiation can be absorbed directly by molecules of organic
compounds. Thus there are excited molecules, ions, radicals and peroxides: RH*, RH+,
•
R, •RO2.
Further intercept of energy of free radicals by other materials (most active
reductants) is carried out.
Chemically high-activity compounds formed at this stage enter reactions with
other biochemical compounds of an alive organism that gives in infringements of
biochemical processes and structures of cells, hence, and to infringements of functions
at a level of a complete organism.
Indirect action of radiation
The chemical one after another chemical and biochemical reactions can promptly
grow, getting character of the chain branched reactions. The activity of an ionizing
radiation caused by products of a radiolysis of water is termed as indirect activity
of radiation.
The proof of the important role of products of a water radiolysis in formation of
consequences of an irradiation is higher radiostability of dry and powdered enzymes in
comparison with their water solutions.
Free radicals and peroxides are capable to vary chemical composition of DNA.
Unsaturated fatty acids, amino acids and phenolums are exposed to an oxidizing,
therefore are formed lipid (lipid peroxides, aldehydes, ketones) and quinones
radiotoxins. Radiotoxins depress synthesis of nucleic acids, react on DNA molecule as
chemical mutagen, vary activity of enzymes, and react with lipid-albuminous
endocellular membranes.
Thus, initial radiochemical reactions consist in direct and indirect (through
products of water radiolysis and radiotoxins) damage of the major biochemical
components of a cell – nucleic acids, proteins, enzymes. Further enzymatic reactions
roughly vary – strengthens enzymic decay of proteins and nucleic acids, synthesis of
DNA is reduced; the biosynthesis of proteins and enzymes is broken.
Infringement of vital activity of cells
All organoids of a cell are damaged owing to the described changes. Lesions of a
nucleus – aberration chromosomes (breakages, rearrangements, a fragmentation),
chromosomal and genovariations (genetic mutation) break inheritable properties of a
cell. Division of a cell is inhibited or proceeds abnormally. At the moment of division,
and also in an interphase the cell can be lost.
131
Endocellular membranes – membranes of a nucleus, mitochondrions, lysosomes,
endoplasmic reticulum – are damaged. From the defective lysosomes enzymes which
damage nucleic acids, cytoplasmic and nuclear proteins are released. Infringement of
energy metabolism of a cell is one of the causes of a stopping of nucleic acids and
nuclear proteins synthesis, as inhibitions of mitosis.
The nucleus of a cell has especially high radiosensitiveness in comparison with
cytoplasm.
Therefore cells of tissues, in which processes of division are most intensive and
constant, perish at an irradiating even in small doses. They are, first of all, thymus
gland, sexual glands, hemopoietic and adenoid tissue.
The epithelial tissue (in particular a glandular epithelium of alimentary and
sexual glands, an integumentary epithelium of a skin, then an endothelium of vessels) is
following on radiosensitiveness.
Cartilaginous, osteal, muscular and nervous tissues are radioresistant.
Nervous cells have no ability to division and consequently perish only at activity
on them radiation in major doses (interphasic destruction). Mature lymphocytes, which
perish even at an irradiating in a dose 0,01 Gy, are exception of this rule.
The basic symptom-complexes of i nfri ngeme nt of functions of a n
organism.
At an irradiating of lethal and superlethal doses interphasic destruction of cells
prevails; the death comes the nearest minutes or hours after an irradiating. At an
irradiating medial doses life is possible, but in all without exception the functional
systems pathological changes move. Their intensity is in dependence on a relative
radiosensitiveness of tissues.
Infri ngeme nt of a he mopoiesis and blood system is most typical.
The quantity of all blood cells decreases, cells become functionally incomplete. At the
first hours after an irradiating the lymphopenia, later – a disadvantage of granulocytes,
thrombocytes and even later – erythrocytes is noted. Exhausting of a bone marrow is
possible.
T he immune reactivit y is reduce d. Immunodefence is depressed,
therefore an infection is the earliest and serious complication of an irradiating. The
infection develops in an intestine; there is an adsorption of toxins and bacteria into a
blood. Infringement of function of a digestive tract gives in an attrition of an organism.
T he hemorrhagic s yndrome is the typical attribute of radiation sickness.
The quantity of thrombocytes is reduced, as well as their ability to coagglutination, the
molecular structure of fibrinogenum variates, in a blood there are anticoagulants,
mechanisms of protection of a vascular wall are broken. All this promotes to
hemorrhages.
Circulations in capillaries it is disturbed due to a developing stasis that enhances
a lesion of tissues.
In nervous s ystem rasping structural changes and destruction of nervous
cells come at rather high exposure doses. Therefore the functional changes are evident
in the beginning, since in some seconds after irradiating nervous receptors are exposed
to an irritation by products of radiolysis and disintegration of tissues. Nervous-reflex
activity is broken before appearance of other typical signs of a radiation sickness.
The lens is the most vulnerable for radiation a part of an eye. The lost cells
become opaque, and growth of the turbid fields brings at first to a cataract, and then to
the complete blindness. The greater dose, the more loss of sight. The grown turbid
fields can be formed at exposure doses 2 Gy and less. More serious form of a lesion of
an eye – a progressing cataract – is observed at doses about 5 Gy. The professional
irradiating harmful for an eye: doses from 0,5 up to 2 Gy, received during 10–20 years,
give in augmentation of density and a phacoscotasmus [lenticular opacity, opacity of
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lens cataract].
In organs of endocrine system primary attributes of activity rising are
replaced by depression of endocrine glands function. Single exposition of spermaries at
a dose only in 0,1 Gy gives in a time sterility of men, and doses from above 2 Gy
can give in a permanent sterility.
Owing to chromosomal damages somatic cells can undergo to a malignant
degeneration, and aberration chromosomes in sex cells give in development of
hereditary diseases. A cancer is most serious of all consequences of an irradiating
of the human at small doses.
Children are extremely sensitive to activity of radiation. The age of the child
less, the bones grows is more strongly depressed. A cooperative dose about 10
Gy, received within several weeks at a daily irradiating, it happens enough to cause
some anomalies of a skeletogeny.
Dosimetry. Doses of the ionizing irradiation
Dosimetry is an essential part of radiation science.
Exposure doses
Absorbed dose – the energy of an ionizing radiation absorbed by the irradiated
body (substance or tissues of an organism), in recalculation on a mass unit.
Equivalent dose – an absorbed dose increased on coefficient, reflecting ability of
the given kind of radiation to damage a tissue of an organism.
Effective equivalent dose the equivalent dose increased on coefficient, taking
into account different sensitivity of various tissues to an irradiation.
Collective effective equivalent dose – the effective equivalent dose received by
group of people from any radiant of radiation.
Complete collective effective equivalent dose – a collective effective
equivalent dose which will be received with generations of people from any radiant for
all time of its further existence.
Absorbed dose
The radiobiological effect of ionizing radiation is the greater the greater the
radiation energy absorbed by the substance. The amount of absorbed radiation is
determined by a dose, i.e. quantity of an absorbed energy. Influence of the radiation on
objects can be characterized by the ratio of radiation energy (E) absorbed by the
object's material, to the mass (m) of this material, irrespectively of its source. This
characteristic is known as the radiation dose or absorbed dose (D):
D=E/m.
The current unit of absorbed dose in a SI is the gray (Gy). Represents quantity
of energy of the ionizing radiation absorbed by a mass unit of any physical body, for
example tissues of an organism.
1 Gy = 100 rad = 1 J/kg. It’s mean that 1 kg of material absorbs 1 J of energy of
ionizing radiation.
The rad was the original unit of absorbed dose. It is an off-system unit for the
radiation dose.
1 rad=10–2 Gy=102 erg/g; 1 Gy=100 rad. 1 erg = 10–7 J.
One rad corresponds to the absorption of 6.242 x 1013 eV by one gram of
substance for any type of ionizing radiation. Although the basic concept of the rad is
unambiguous, it is often difficult to calculate the absorbed dose in a given system.
Absorbed dose is an average quantity for a macroscopic material. The local dose in
different regions of the absorber may vary owing to the production of secondary ionizing
particles or electromagnetic radiation (EMR) which contribute to the dose in other
133
regions of the material.
Exposure dose of photonic radiation (X- or γ-radiation) is measured by value
equal to ratio of sum of electric charges of all same charge (one-sign) ions (Q) which
are produced by electrons under the affect of X-radiation or γ-radiation to the mass of
this air (m):
X=Q/m.
In the SI the unit of exposure dose is coulomb per kilogram (C/kg).
In practice, a widely used off-system unit of the exposure dose is roentgen (R). It
is one of the first unities of X-ray and γ-radiations dose. One roentgen is the dose of Xradiation or γ-radiation, under the affect of which, at total ionization in 1 cm3 of air under
normal conditions (temperature 0°C and pressure 760 mm Hg), 2.08·109 pairs of ions of
each sign are formed. 1 R=2,58•10–4 C/kg.
1 roentgen (1 R) – such X-ray or γ radiations dose at which 1 g of air absorbs 84
erg of energy at 0°С temperature and 760 mm hg atmospheric pressure.
Unity is applied to dosage measurement of any ionizing radiation exposure doses
– a physical roentgen-equivalent (rep). It is a dose of any ionizing radiation at which 1 g
of materials absorbs 84 erg – as much, how many as 1 g of air absorbs at 1 R
electromagnetic radiation.
This unit is difficult to measure and not often used today.
Ratio of the radiation dose to the time of exposure is known as the dose rate or
exposure rate (Ď). Ď =D/t.
It unit is grey per second (Gy/s) or rad per second (rad/s). In practice, it is difficult
to measure the dose rate. Hence, the radiation dose absorbed by a body is estimated
by measuring the degree of ionization of air ambient to the body.
Fluence (F) [integrated flux density] is a unit of exposure dose defined as the
number of particles or amount of energy incident per unit area.
Fluence rate is the fluence per unit time. "Flux" is often used in neutron physics
in lieu of fluence rate. This usage is confusing because radiant flux is a power unit in
optical physics with the units of watts.
Equivalent dose
Other units of absorbed dose have been employed to express the biological
effectiveness of a given radiation.
The biological effect of radiation depends on an ionic density which is measured
by number of ions pairs formed on 1 micron of a particle trajectory.
The ionic density is proportional to a quadrate of a charge and in inverse
proportion to particle velocity. As at peer energies velocity of a particle is inversely
proportional to particle mass that the ionic density will be directly proportional to mass of
a particle. Therefore at identical energies the greatest ionic density is given with the αparticles having the greatest charge and the greatest mass. The least ionic density is
given with electrons, X-ray and γ-ray. Protons, neutrons and deuterons occupy the
intermediate standing between the first and second groups of radiation.
The rem (roentgen-equivalent-man) [biological equivalent of roentgen] is the
dose in rad multiplied by a relative biological effectiveness (RBE) factor. For unity the
relative biological effectiveness is accepted efficiency of X-ray with energy 200 keV.
The RBE is taken as unity for "hard" X-rays and γ-rays and may be much higher for
other types of radiation, for example, the RBE is about 20 for fast neutrons.
Drem = Drep ·RBE,
where D — radiation absorbed dose,
or in standard signs:
H = D·q,
where H – equivalent dose, D — radiation absorbed dose, q – quality coefficient
(RBE factor, table 15.4). H is measured in rem or sievert, D – in rep or coulomb per
kilogram correspondingly.
134
Unit of aggregate exposure dose of particular group of people is person-rem.
An alternative unit of the equivalent dose in a SI-system is the sievert (Sv) which
equals 100 rem. 1Sv=100 rem. Represents unity of an absorbed dose multiplied on
coefficient, taking into account unequal radiative danger to an organism of different
kinds of an ionizing radiation. 1 sievert corresponds to an absorbed dose in 1 J/kg for Xray, γ- and β-radiations.
Because the rem is a relatively large unit, typical equivalent dose is measured in
millirem (mrem), 10–3 rem, or in microsievert (μSv), 10–6 Sv. 1 mrem = 10 μSv.
Thus, the dose in Sv and Gy are the same for RBE = 1. The maximum
permissible lifetime radiation exposure is 5 mSv in the U.S. for the general population,
which is equivalent to 0.5 rad of X-rays and gamma-rays. This is 0,1% of the expected
lethal dose for a whole body exposure.
Natural sources of ionizing radiation create a certain radiation level that
continuously affects all the organisms on Earth. This level is known as the
“background”. The annual equivalent dose related to the natural background is usually
equal to 125 to 300 mrem (1,25–3 mSv) for most of people.
In medicine the maximum permissible dose is used. The maximum permissible
dose is the maximum value of an individual annual equivalent dose, which, at uniform
exposure during 50 years, shall have no detrimental effect on man's health. The
maximum permissible annual equivalent dose for professional exposure is equal to 5
rem.
Relative biological effectiveness value for different kinds of radiation
Kind of radiation
RBE
X-rays and γ-rays
1
β-particles and electrons
1
α-particles and protons
10
Slow neutrons (energy less 1 keV)
3
Fast neutrons (energy more 100 keV, before 20 MeV)
10
Multicharged ions (polyvalent ions) and recoil nuclei
20
Different organs and tissues have different sensitivity: for example, at an
identical equivalent exposure dose originating of a cancer in lungs is more
probable, than in a thyroid gland, and an irradiation of sexual glands especially
dangerously because of hazard of genetic damages. Still in 1906 I. Bergonje and
L. Tribondo have formulated a rule: sensitivity of cells to an irradiation is directly
proportional to them proliferative activity and inversely proportional degrees of their
differentiation. After multiplying of the equivalent doses on the corresponding
coefficients (see table below) and summation on all organs and tissues, we shall
receive the effective equivalent dose reflecting a cooperative effect of an
irradiation for an organism; it also is measured in sievert.
The weight coefficient accounting for the contribution of the tissue (organ) to the
body's total radiosensitivity
Tissue or organ
W
Gonads
0,2
Red bone marrow
0,12
Large intestine
0,12
Lungs
0,12
Stomach
0,12
Urinary bladder
0,05
Mammary gland
0,05
Liver
0,05
Esophagus
0,05
135
Tissue or organ
W
Thyroid gland
0,05
Skin
0,01
Periosteum
0,01
After summation of the individual effective equivalent doses received by group
of people, we shall come to a collective effective equivalent dose which is
measured in person-sievert (person-Sv).
As many radioactive materials decay very slowly also will be the active in the
long-term future too, that collective effective dose which will be received with many
generations of people from any radioactive source for all time of its further existence,
term as an expected (complete) collective effective equivalent dose.
Dose rate
Dose rate is dose of irradiation in a unit of time. Dose rates can be calculated for
all before-mentioned dosimetric characteristics. They can use, for example, if it is
necessary to calculate influence of some permanent active source of radiation: native or
professional sources. They ca calculate in day, in year and so on.
For evaluation of population radiation risk it is used such unit as mSv/year.
Dosimetry
Instruments used for detecting ionizing radiation, determining their
characteristics, and measuring radiation doses can be divided into two groups:
detectors of ionizing radiation and dosimeters.
Detectors of ionizing radiation. Ionizing radiation detectors are intended for
registering radiation and measuring some of their characteristics (e.g., energy and
velocity of particles, the ratio of their charge to mass, and others). Detectors can be
referred to three groups: track detectors, counters and integral devices.
Output measurement
Sensor –
Y
(registering) apparatus
nuclear radiation
Amplifier
detector
Fig.1. The general scheme of all dosimeters.
Track detectors allow to observe particle path, counters register particle
appearance in device chamber, integral devices give information about ionizing radiant
flux.
Track detectors include the Wilson chamber, the bubble chamber, spark
chamber, thick-layer photo plates. Counters are proportional counter, the Geiger
counter and others.
In the Wilson chamber (cloud chamber, expansion chamber, fog chamber or
diffusion chamber) there are saturated pairs of any fluid, which are made
supersaturated by sharp magnification of volume of the chamber.
The chamber is in a magnetic field. Ionizing particles flying in this moment
through the chamber leave tracks as fluid droplets condensed on the ions formed by
particles. Tracks are photographed. The shape and volume of a track depends on a
charge of a particle, its mass and energy.
In bubble chamber (bubble cell) there is a superheated fluid, and the flying
particle produces an ebullition (boil) and formation of pair bubbles. Registering
descends as in an expansion chamber.
In thick-layer photo plates particles leave tracks on emulsion which becomes
visible after development of photo plates.
In the capacity of an instance of gas devices we shall consider a Geiger-Muller
counter; it will consist of coaxially located cylindrical electrodes (fig.2): 1 – the
cathode (a metal evaporated on a glass tube, 3 – the anode (the thin hairline tensioned
X
136
along an axis). Pressure of gas inside the counter is of 100-200 mm Hg. The voltage
about several hundreds volts is created between electrodes. The ionizing particle,
flying by in the chamber, ionizes atoms of gas; the formed free electrons move to
the anode. Electrons near to a thread are sped up so, that begin ionize gas. In
result there is a discharge and a current flows in a circuit.
Fig.2. Scheme of Geiger counter camera. 1 – sealed tube (gas filled); 2 – to
electronics; 3 – anode (wire at high voltage stretched along axis); 4 – particle
track; 5 –
primary electrons; 6 – electron avalanche.
It is necessary to extinguish the self-sustained discharge in a Geiger-Muller
counter, differently the counter will not react to the following particle. To
quenching the discharge there are applying a radio engineering method and a
method based on addition of polyatomic gases in a tube (self-quenched counters).
The electrical impulses incipient in an external circuit are strengthened and
filed by the special device.
Scintillation (luminescent) counter counts short-term flashouts of light –
scintillations which descend in some materials under activity of an ionizing radiation.
In the luminescent counter they are filed automatically with use of the
photomultiplier tube.
Semiconductor counters react to change of an electrical conduction of p-n
junction under action of a charged particle.
X-ray and γ radiations are filed due to ionization which is invoked by the charged
particles formed at a photoeffect, the Compton effect, etc.
Counters should meet some general requirements, such, as the efficiency,
resolvent time, etc. Efficiency is the relation of the registered number particles to general
number of the particles which has flown by through the counter. Resolvent (or dead) time
of the counter is the minimum time which should part the particles following one after
another that they have not been counted as one.
Dosimeters are devices for measuring doses of ionizing radiation, or values
related to doses. Depending on the physical phenomenon determining the dosimeter's
principle of operation is based, the following devices are distinguished: ionization,
luminescent, semiconductor and photo dosimeters.
Radiometers are the devices applied to measuring activity or concentration of
radioactive isotopes.
Self-control material:
B. Test tasks (α=ІІ)
1. What is law for determination of weakening of ionizing radiation in substabce?
A) Mozli law
B) Bouguer law
C) Plank law
D) Einstein law
2. What are radiotoxins?
A) Substabces amplified toxic effect of irradiation;
B) Toxical compound formed in irradiated tissues;
C) Toxic substances, which toxic effect is amplified by irradiation.
3. What is Bouguer law?
137
A) Φ = Φ0e–μt.
B) I = dn/dl.
dR
C) S 
.
dl
t
D) N  N    T .


mv
.

4. Unity of an absorbed dose of an ionizing radiation in SI is:
A. Roentgen
B. Coulomb per kilogramme
C. Sievert
D. Grey
E. Kerma
5. Unity of an exposition dose of a photon ionizing radiation in SI is:
A. Coulomb per kilogramme
B. Grey
C. Sievert
D. Kerma
E. Roentgen
6. Unity of the equivalent dose of an ionizing radiation in SI is:
A. Roentgen
B. Coulomb per kilogramme
C. Grey D. Sievert
E. Kerma
7. Unity of an exposition dose of a photon ionizing radiation in SI is:
A. A coulomb per kilogramme
B. Grey
C. Sievert D. Kerma
E. Roentgen
Literature recommended
Main sources.
─ Lecture.
─ Chaliy at all., Biological and medical physics. – Kiyv, 2009.
─ L.D.Korovina. Biophysics with beginnings of mathematical analysis and statistics.
Extended course of lectures. – Vol.3. Optics. Quantum phenomena. – Poltava,
2014.
Additional textbook, journals and references::
─ Compendium of Medical Physics, Medical Technology and Biophysics for
students, physicians and researchers. Nico A.M. Schellart. – Department of
Biomedical Engineering and Physics Academic Medical Center University of
Amsterdam.– Amsterdam.– 2009 (electronic book).
─ Roland Glaser. Biophysics: An Introduction.– 2010.
─ Philip Nelson. Biological Physics (Updated Edition).– 2007.
─ Paul Davidovits. Physics in Biology and Medicine, Third Edition (Complementary
Science). – 2007.
─ Bengt Nölting. Methods in Modern Biophysics.– 2009.
E) E 
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