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Essentials
of nuclear medicine
Medical imaging
CT
Rtg
X- rays
usg
Ultrasound
MR
Nuclear Magnetic Resonance
Nuclear Medicine
SPECT
PET
A conventional radiological, ultrasound and magnetic resonance
diagnostics is of morphological character, i.e. the imaging using these
modalities gives insight into the structure of human tissues and
organs. As such these modalities enable detection of foci or regions
of abnormal composition:
 the radiological image visualises differences in intensity of X-ray
absorption
 ultrasound image reflects different echogenicity by registration of
acoustic wave reflection by structures of varying acoustic
resistance (impedance)
 imaging by magnetic resonance modality records local changes in
intensity of magnetic field which occur while absorbing
electromagnetic waves of radiofrequency by atomic nuclei
contained in a uniform magnetic field of high intensity. The
resulting image reflects spatial distribution of such atomic nuclei
(mostly commonly protons – nuclei of hydrogen atoms) and their
chemical bounds.
Nuclear medicine
This modality uses radionuclides (radioactive
atoms) introduced into human body in form of
unsealed sources of radiation (in form of
radiopharmaceuticals and sometimes also in
atomic form, e.g. noble gases) for purposes of
diagnostics and therapy.
Atomic structure
A
Z
protons
X
neutrons
A – mass number – a sum
of protons and neutrons
in an atomic nucleus
Z-atomic number – a number
of protons in the atom of a
given element
electrons
Isotopes
Variants of the same element differing in numbers
of neutrons (A) in the nucleus
Hydrogen isotopes
Radionuclides
Atoms of elements with unstable nuclei, undergoing
spontaneous decay with emission of energy (photons,
particles)
Atomic nucleus
electromagnetic quanta
(photons γ)
charged particles
(β – electrons, positrons,
α – particles)
Radiations emitted as a result of radioactive
decay
Photons (gamma)
Penetrating the tissue and leaving the body
Particles (beta rays)
- electrons with negative charge
- positrons with positive charge.
Maximum range in tissues – a few mm.
alfa particles (helium nuclei).
Maximum range in tissues – a few tens of
μm
Quantities characterizing
the radioactive decay
- Half-life – time needed for decay of 50% of the
initially present atoms of radionuclide.
- Activity – number of radioactive decays in a given
sample per unit of time
Unit: Becquerel (1 Bq) = 1 decay/sec
1 MBq = 106 Becquerel
- Energy of emitted photons and particles
Unit:
eV – electronvolt
Radionuclides used
in nuclear medicine
Diagnostics: emitters of gamma rays with half-lives
from a few hours to several tens of hours, for
instance: technetium - 99mTc, iodine – 131I, 123I,
indium – 111In, thallium – 201Tl, gallium – 67Ga;
emitters of positrons – b+ particles (PET): 18F, 11C,
15O, 68Ga, etc.
Therapy: emitters of b- particles with range
of a few mm, for instance: iodine - 131I,
strontium – 89Sr, samarium – 153Sm, renium –
186Re, ytrium - 90Y, lutetium - 177Lu
(emitters of a particles under consideration –
experimental and clinical tests: astatine - 211At,
bismuth - 212/213Bi)
Nuclear
Medycyna
nuklearna
medicine
99m
Tc
Radioactive technetium 99mTc, (a metastable
radionuclide), is the most frequently used radioisotope
in nuclear medicine. This is due to:
low dose of radiation absorbed in a patient body (short half life of
6h, very low contribution of electrons to the energy emitted)
Energy of emitted gamma rays (140 keV) well suited to detection
by scintillation camera
High chemical reactivity of the element, which is prone to form
complexes with a wide range of chemical compounds (ligands)
Due to the fact that 99mTc atoms originate from decay of 99Mo it
can be obtained from Mo/Tc generators in every nuclear medicine
lab, day by day for ab 10 days (restoration of the radioactive
equilibrium between 99Mo and 99mTc)
Radiopharmaceutical
This is a substance containing a radioactive atom in
the molecule, which emits gamma rays that can be
utilized for diagnostics or charged particles (alfa,
beta minus) of very short range in tissues that may
kill cells in the vicinity of deposited molecules, and
therefore utilized for treatment of pathological
tissue at the site of deposition or in vicinity.
RF
131I
131I↔
Hippuran
Routes of administration of radiopharmaceuticals
By inhalation
Inj. into vertebral
channel
Per os
Inj. intravenously
Introduction into
urinary bladder
Inj. intraarticularly
(joints)
Inj. subcutaneously
Functions of nuclear medicine
Diagnostics
Imaging
(scintigraphy)
Static
scintigraphy
• organs
planar
• whole body
• emission tomography SPECT
• emission tomography PET
}
Therapy
Non-imaging
(eg. clearances, metabolism)
Dynamic
scintigraphy
Nuclear medicine
Diagnostics
Imaging (scintigraphy)
- image generated by emitted photons
- image represents specific function of an organ (normal, pathological)
- Scintigraphy:
1) static (planar or tomography)
provides distribution of activity (2 or 3D), represents functional state of
specific tissues, as well as localization, shape and dimensions of the
organ of interest
2) dynamic
by providing qualitative or quantitative data on passage of the
radiopharmaceutical through a given organ. This may provide
information on organ’s function, e.g. flow of urine via urinary tract,
kinetic behavior of the left heart ventricle, etc, etc.
Resolution of scintigraphic images is inferior to that of US, X-rays or MRI.
A scintigraphic image (scintigram) presents
distribution (2D or 3D) of the activity in
a studied organ (or system); such an
image reflects always a given function of
the organ (normal – physiological or
pathological)
Static scintigraphic image (example)
External detection of radiation by means of scintillation camera
provides information on distribution of administered activity in a given
organ
Example: static scintigraphy of the liver
Liver – normal image
Liver – cancer
Developing tumour destroys the tissue
(including the cells of R.E. system)
In this case after administration of 99mTc labelled colloid in the liver (distribution
reflects regional phagocytic function of the reticulo-endothelial system in liver)
Nonimaging studies utilizing radiopharmaceuticals
Investigation of distribution of radiopharmaceuticals in various
compartments of the system as well as rates of the transfer between
compartments, and elimination from the body (e.g. clearance rates).
Cp
Example
99mTc
DTPA
conc. in plasma
diethylenetriamine
pentaacetic acid
time
This curve can be used for calculation of glomerular filtration rate (GFR)
Nuclear medicine - therapy
Therapy of pathologically altered cells and
tissues using radiation (beta minus and alfa
particles) emitted by radionuclide taken up by
the cells or deposited in their vicinity (within
the range of particles in question)
Nuclear medicine - therapy
The therapy is used for treatment of:
diseases of the thyroid (benign and
malignant)
pains due to malignant metastases into
the skeleton (paliative treatment)
exsudates and proliferation of
the synovia in chronic arthritis
of selected malignancies (receptor
affinity, antibodies)
Scintigraphy
Basic tool: SCINTILLATION CAMERA
collimator
preamplifiers
electrical signals
to console
Gamma ray hits a scintillation
crystal, causing emission of
light photons by a crystal
(scintillations).
Those photons are absorbed
in photocathodes of
photomultiplers releasing
electrons, thus forming an
electrical current, which is
then amplified in
photomultipliers and
registered in form of electrical
signals at the detector output
photomultipliers
photocatode
scintillator
(NaI(Tl) crystal)
collimator (passes only gamma rays moving in a direction parallel to axes of collimator holes)
Scintigraphy
Basic tool: SCINTILLATION CAMERA
Light photons (scintillations)
scintillator
collimator
Distribution of a
radiopharmaceutical in
a given organ is
reflected in a
scintillation crystal in
the form of light
photons.
Coordinates of every
flash event are noted
by a special electronic
system, thus enabling a
2D presentation of a
distribution of a
radiopharmaceutical in
a patient organ.
Localization of every flash event
in x,y coordinates
Origination of a planar scintigram
Digital image
51 cm
n
n
51 cm
Komórki matrycy cyfrowej
Matrix
with pixels
Digital images are in fact matrices of pixels,
presented in colors.
Static scintigraphy
Conditions to be met:
1. Distribution of activity in an organ must not change over the interval of image
acquisition.
2. The acquisition should only start when stable activity level in an organ has
been reached.
Information gathered:
1. Presence or absence of regions in an organ of abnormal (reduced or enhanced)
uptake of the radiopharmaceutical administered.
2. In addition, data on position, shape and magnitude of the organ are obtained
Normal lung perfusion scintigrams
Anterior view
Posterior view
anterior
mediastinum
R silhouette
of heart
posterior
mediastinum
L
L
R
Technetium labeled microspheres (small albumin spheres of diameters comparable to
diameters of capillary arteries in lungs - in micrometers) are trapped in those arteries
thus enabling imaging of lung perfusion.
Whole body static scintigraphy
(skeletal scanning)
Skeleton of an adult
- normal image
Skeleton of a child
- normal image
Abnormal image: numerous
metastases to the skeleton
(cancer)
Bone scintigraphy – an image presenting bone metabolism. Abnormal image – lesions of
enhanced bone metabolism at sites of cancer metastases
Single Photon Emission Computed Tomography (SPECT)
Dynamic model of
3D-activity
distribution
reconstruction
A method for presentation of a distribution of a radiopharmaceutical in 3
dimensions. Study acquisition is performed with a camera detector turning around
a patient body. Then, using a special method for tomographic reconstruction,
organ cuts along respective planes can be obtained.
Single Photon Emission Computed Tomography (SPECT)
Various planes of „cutting” the 3D brain matrix
Brain SPECT perfusion study after Tc-HMPAO administration
Transverse planes (cuts)
From left to right and from top to the bottom: from base to the top of the brain
Dynamic scintigraphy
• The acquisition of scintigraphic information is started
(usually) at the moment of i.v. injection of the RPharm.
• The study consist of a series of scintigraphic image
acquisitions.
• The frequency of image acquisition depends upon the
rate of the studied process.
Dynamic scintigraphy of the urinary system (renoscintigraphy)
Serial acquisition of images takes place continuously over 20 min. (images provide
information recorded over 20 minutes at 1 min intervals)
Renographic curves
counts
Left kidney
Right kidney
Background
Ur. bladder
time
Counts are recorded at acquisition intervals over several regions of interest: kidneys,
urinary bladder and over region representing „the blood in organs background”. Curves
of activity in theses regions are automatically converted into renographic curves.
Principles of Positron Emission Tomography (PET)
Another kind of tomography
used in nuclear medicine.
This modality makes
advantage of radionuclides
emitting positrons. As a
result of a phenomenon of
annihilation of positron with
an electron in a patient
body 2 photons appear
escaping in opposite
directions and they are
detected in PET detector
ring with a coincidence
system.
Positron + electron anihilation
→ 2 photons of 512 keV each
Detector
Detector
Radio- T1/2
nuclide [min]
18F
- 109
15O
- 2,1
11C
- 20,4
13N
- 10
82Rb
- 1,2
Coincidence
system
Preconditions: on site production of positron emitting nuclides in a cyclotron; automatic on site
synthesis of radiopharmaceuticals.
Main benefits: a possibility to use for PET imaging the natural compounds (or their closely related
analogues) of well understood physiological and biochemical behavior.
Disadvantage: high cost
CLEARANCES
Definition:
The volume of plasma completely cleared
of a specific compound (substance S) per
minute and measured as a test of kidneys
or liver function.
There is an obvious relationship between a clearance
and rate of the decline of the substance (S)
concentration in the plasma
lack of
kidneys
Sp(t)
(conc. in
plasma)
reduced
function
A clearance is
calculated as a ratio
of an activity
administered to a
patient and a definite
integral of a function
Sp over the interval
from zero ( moment
of injection) to infinity
The faster
decline of the
curve, the higher
the clearance of
the substance.
normal
function
t
CL =
4
A0
I S (t)dt
p
0
(Activity of subst. S administered to a patient )
(Area under the curve presenting declining
concentration of substance S in plasma)
Determination of kidney and liver clearances
- the selected RPhs
GFR - 99mTc DTPA
ERPF - 131I orthohipuric acid
- 99mTc MAG3
- 99mTc Ethylene dicystein (EC)
Clliver - 99mTc Hepida
(derivative of an imin-bi-acetic acid)
Advantages of radionuclide methods:
 high accuracy of determination of plasma concentrations
 possibility to measure CL after a single intravenous injection
 determination of CL is possible without collection of urine or gall
 low labour input required (particularly for simplified procedure, based on
one sample of blood).
Patients’ care in nuclear diagnostics or therapy
General information
1. Diagnostics or therapy by means of radiopharmaceuticals
are in general non-invasive (there are very few exceptions
e.g. intraarticular administration).
2. Majority of diagnostic procedures of nuclear medicine do not require
pretreatment of the patient (there are a few exceptions).
3. Administration of a radiopharmaceutical is not followed by
complications resulting from hypersensitivity (this applies also to
patients hypersensitive to iodine contained in contrast media).
4. Doses to patients of ionizing radiation, resulting from diagnostic
procedures are small, comparable to those accompanying most common
radiological examinations.
5. Doses to the personnel injecting the radiopharmaceuticals to patients
are very small if appropriate syringe shields are used and the patient
has been prepared by introduction a venflon needle into his/her vein
prior to injection.