Download Digital: Chapter One

Chapter 1: What Is Digital Imaging?
What is Digital Imaging?
Digital Imaging is the transforming of energy:
(from light photon, sonic, magnetic, x-ray, or
gamma radiation sources) to electrical signals
that are measured and assigned discrete binary
values.
Binary data is processed into image information
which may be enhanced, printed, displayed on a
monitor, and stored as a computer file.
Digital Modalitites
Every imaging modality may be digital. Some are
only digital.
From an equipment standpoint, the major difference
between the modalities is the type of energy used,
how the energy is changed as is traverses the body,
and how the remnant energy is measured as it leaves
the body.
Computed Tomography (CT)
Is only digital
X-radiation passes through,
and is attenuated by the atomic
composition of cells and tissues.
Cardiovascular Interventional
Technology (CVI) digital application started in the 1980s
X-radiation passes through,
and is attenuated by the atomic
composition of cells and tissues.
Magnetic Resonance Imaging (MRI)
Is only digital
Hydrogen atoms
excited by radio
frequencies (RF)
create magnetic
vectors that sweep
an antenna.
Nuclear Medicine Technology
An isotope is injected, ingested
or inhaled. After being
metabolized, concentrations of
the isotope are collected by the
nuclear medicine camera.
Diagnostic Medical Sonography
and Vascular Technology
Sound waves pass into, and
are reflected off of interfaces
of tissues and organs.
Digital Radiography (DR)
Digital applications were available in the early 1980s, but the
difficulties of displaying radiographic quality images (in terms of
spatial resolution) made it unpopular. In the year 2000 it was
beginning to be accepted.
X-radiation passes through,
and is attenuated by the atomic
composition of cells and tissues.
Digital Mammography
X-radiation passes through, and is attenuated by the atomic
composition of cells and tissues. Like digital radiography,
highly dependant on excellent spatial resolution.
Digital Fluoroscopy (DF)
R/F Digital C-Arm
Question: How is an analog
radiographic image made?
• Begin with photons
coming off the anode.
• Outline the process,
step by step.
• Use the appropriate
terminology.
Incident, Attenuation, Remnant radiation, Latent, Manifest
Answer: How does a
radiographic image get on a film?
• Incident beam leaves anode.
• Attenuation in body.
• Remnant radiation exits in pattern of
anatomy.
• Photons interact with silver halide crystals.
• Latent image is formed.
• Manifest image on development.
Question: What does a graphic
representation of density building
on a film look like, and what is it
called?
D log E (or)
H & D Curve (or)
Hurter & Driffield Curve (or)
Characteristic Curve (or)
Sensitometric Curve
Producing a digital radiograph is the
same as for analog film, up to the point
of the photons interacting with the film.
Digital imaging samples the remnant
radiation with (some kind of) a detector,
not film.
Analog : The continuous build up
of density on a radiographic film
is an analog process.
For Example:Analog Time
• The passage of time as
recorded on a watch
with a continuoussweep secondhand is
an example of an
analog measurement of
time.
Digital Time
• The passage of time as
recorded on a digital
clock, in discrete
values, is an example
of a digital process
Analog is continuous.
Digital is discrete.
Computer circuitry is made up
of a series of switches that store
data in one of two elementary
-discrete- states: on, or off.
Open
=0
Closed
=1
0 and 1 are the only two numbers
used in the binary (two numbers)
numbering system
0 and 1 are
binary digits
or bits
Digital computers
store data as binary
digits.
Pascal’s calculator - 1642
A mechanical
device, not
programmable
A series of gears, turned by hand, rotated a wheel with numbers
that showed in a window. When the number in the ones column
reached nine, it turned the wheel in the tens column to 1, and
the ones column returned to zero.
Pascal invented his device to relieve the fatigue of spirit
associated with the work of doing arithmetic.
Jacquard’s Loom - 1804
Instructions for weaving
patterns into cloth were fed
into Jacquard’s machine
by this early version of
punched cards that were
made of wood.
The red arrows show the
cards entering and leaving
the machine.
A mechanical device,
that was programmable
Babbage’s Difference Engine - 1822
A crank was turned to perform a mechanical progression
of numbered gears in columns that, like Pascal’s calculator,
represented increasing powers of ten.
Hollerith’s tabulator
In 1880 it took 9 years to tally
the results of the US census.
Herman Hollerith built an
electromechanical calculator
that used punched cards to
input data on the population
(age, gender, numbers in
family, etc), and reduced the
time to do it in half, on a
greater population, with a
more detailed analysis.
Like Pacal’s calculator, and Babbage’s difference engine numbers
were carried over from one column to the next. The great advantage
of this device was the use of electric motors to drive mechanical
parts, and punched cards to input data.
George Boole
1815-1864
Mark I - 1944
An electromechanical
device, that was
programmable.
The gears of its predecessors were replaced by mechanical
switches. Electric motors, were used to drive the mechanics
that opened and closed the switches, and punched cards were
used to input data.
AND Gate
Off
+
Off = Off
On
+
Off = Off
On
+
On = On
OR Gate
Off
+
Off = Off
On
On
+
+
Off = On
On = On
NOT Gate
Off = On
On = Off
Operation of a Half Adder
0
+
0
0
0
=0
Operation of a Half Adder
1
+
0
0
1
=1
Operation of a Half Adder
0
+
1
0
1
=1
Operation of a Half Adder
1
+
1
1
0
=2
Three Things a Computer Does
1. Arithmetic functions
2. Comparison functions
3. Memory
Accomplished with accuracy and speed
ENIAC - 1946
The first fully electronic calculator used 18,000 vacuum tubes
that replaced the switches of Mark I. The input of data was
accomplished by turning knobs, reconfiguring telephone
patch cords, and punched cards.
UNIVAC I - 1951
“Computers of the
future may weigh no
more than 1.5 tons.”
Popular Science, 1949
The first commercial computer sold in the United States.
UNIVAC was build by the inventors of ENIAC, J Presper
Eckert, and John Machly.
Vacuum Tubes and Transistors
Vacuum tube: When the grid is positively
charged electrons are drawn from the cathode
to the anode, creating a closed circuit (1).
When the grid is negatively charged electrons
are repelled, and circuit is open (0).
Grid
Cathode
Transistors: Similar in principle to the
Anode
operation of a vacuum tube. The solid
state semi-conducting material allowed
this switching device to use less energy
and produce less heat in a smaller
component.
Vacuum tube, Transistor, and IC
Integrated Circuits
Within an integrated circuit (IC)
are millions, billions, or trillions
of AND, OR, and NOT gates
embedded in the layers of the
miniaturized circuits of the
semi-conductor material.
Silicon wafers are manufactured
in clean rooms to prevent the
smallest contaminate from being
introduced.
Generations of Electronic Computing
1st - 1951- 57
Vacuum tubes
2nd - 1958 - 63
Transistors
3rd - 1964 - 69
Integrated circuits
4th - 1970 - 90
Very large scale integration (VLSI)
leading to the microprocessor (computer in
single chip).
5th - 1999 -
Age of connectivity
Binary numbering
2
4
3
2
1
0
2 2 2 2
512 256 128 64 32 16 8 4 2 1
0
0
0
0
0
0
1
1 1
0
0
1
1 1 1 0 = 14
1 0 1 0 = 42
1 1 1 1 = 127
Binary numbering
512 256 128 64 32 16 8 4 2 1
1
84
0
1
0 1 0 0
Binary numbering
512 256 128 64 32 16 8 4 2 1
1
1
0
0
384
400
1
0 0 0 0
Picture Elements
(PIXELS)
One Pixel
An image displayed on
a monitor is comprised
of individual dots called
pixels.
One bit of computer memory (on or off)
is all it takes to light up a pixel, or not.
Picture Elements
(PIXELS)
The sum of the pixels
in an image display
forms a matrix
21 Scale of Contrast
MRI: Mid-sagittal
plane, brain scan.
Scale of contrast 21
Only one bit of data
is needed to control
each pixel: on or
off.
Question: How can a simple
on/off switch be used to store
complex information that
contains many shades of gray?
Answer: Many switches are
used in combination.
On/off switches are arranged in groups
of eight in the computer’s circuitry
Eight bits = one byte
CC
Consider the expanded gray scale of two switches in combination.
(Chapter 2 has a complete explanation of the binary numbering system.)
Black
OFF OFF
Dark gray
OFF
ON
Light gray
ON OFF
White
ON
ON
In addition to turning the electron been on and off, a second switch
stores values that control the quantity of electrons in the beam,
creating a gray scale.
With enough bytes of memory, any
number can be represented by
combinations of binary digits
16
8
4
2
1
on
off
on
1
0
1
=5
1
1
1
=7
Printout of the data
in the matrix of a
CT image
250
The number 47 defines the
shade of gray for the pixel
in column 250, row 210.
Values of digits stored in bytes of computer memory directly
correspond to the illumination of pixels.
Column 250
Row 210
In this case, the pixel in column 250, row 210.
A representation of a CT section as image data,
analogous to a paint-by-numbers drawing
Question: If one bit of data is
enough to turn a pixel off or on,
what can a byte of data do for a
single pixel?
Answer: A byte of image data stores
values for 256 shades of gray.
(Chapter 2 has a complete explanation of the binary numbering system.)
How many KB of computer memory is
required for a monitor with a 512 x 512
matrix displaying a gray scale of 2?
512 x 512 = 262,144 bits
262,144 / 8 bits per byte = 32,768 bytes
32,768 bytes / 1024 bytes in a kilobyte = 32KB
Answer = 32KB
How many bytes of computer memory is
required for a for a monitor with a 512 x 512
matrix, displaying 256 shades of gray (28 )?
512 x 512 = 262,144 bits
262,144(8bits)/8 bits per bytes = 262,144 bytes
262,144 bytes/1024 bytes in a kilobyte =262KB
Answer = 262KB
Conclusion: Images are
memory hogs.