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Medical X-ray
Imaging System
Imaging Science Fundamentals
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Medical X-ray Systems
 Chest
x-rays (Abnormalities in lungs, heart,
other abdominal organs, broken ribs)
 Mammography (Calcifications/abnormalities
in breast tissues)
 Dental x-ray (Cavities, wisdom teeth)
 Others include detecting broken bones.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Typical Imaging Chain for
Medical X-ray Systems
processing
X-ray source
Collimator
Imaging Science Fundamentals
Object
Film
Image
Chester F. Carlson Center for Imaging Science
Electromagnetic Radiation



EM radiation can be thought of as oscillating electric
field which generates oscillating magnetic field
which generates oscillating electric field…and so on.
Can also be thought of as photons (particles), as in
CCD detection of visible light.
This is called the “wave-particle duality” of EMR.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Wavelength


(lambda) is called wavelength, the distance
between two identical points on a wave.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Frequency
time
unit of time
 (nu)
is called frequency, the number of
cycles per unit of time.
 It is inversely proportional to the wavelength.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Wavelength and Frequency Relation: review
 =v/




Wavelength is proportional to the velocity, v.
Wavelength is inversely proportional to the frequency.
eg. AM radio wave has a large wavelength (~200 m), therefore it
has a low frequency (~KHz range).
In the case of EM radiation, the equation becomes
=c/
Where c is the speed of light: 3 x 108m/s
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Photons: review
 Photons
are little “packets” of energy.
 Each photon’s energy is proportional to its
frequency.
 A photon’s energy is represented by “h”
E = h
Energy = (Planck’s constant) x (frequency of photon)
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
X-Rays
10-11 m (0.01 nm)
“hard”
10-9 m (1 nm)
“soft”
 Usually
detected as particles of energy (photons).
 Discovered in 1895 by Wilhelm Conrad Roentgen.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
X-Ray Production
Cathode(-)
eeAnode (+)
 Electrons
h
h
are accelerated from cathode to
anode.
 When high energy electrons hit atoms of
heavy metals, the atoms produce X-ray
photons.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Object
 What
can happen to an X-ray when it
encounters the object to be imaged?
Passes
right through the object.
Absorbed completely by the object.
Scattered by the object
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Attenuation Coefficient
5
Attenuation
Coefficient
Bone
Muscle
Fat
1
0.1
10
50
100
150
500
Photon Energy (keV)
Attenuation coefficients tell you the “x-ray blocking power” of a material.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Attenuation Coefficient
 Coefficient
depends on the property of
the material.
 Density
(Bone has a high density compared
to soft tissues)
 Chemical Make-up (Lead blocks x-rays;
lead screening used to protect patient &
technicians)
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Detector
Exposure
(Capture)
Processing
Image
A
special photographic film is used to
capture the x-ray photons which passed
through the object.
 The film is then processed.
 Film turns dark where it was exposed
to x-ray photons.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Typical X-Ray Images
X-ray image of hand
Dental X-ray
Mammogram
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Image Quality Factors
 Source
 Energy
of the photons
 Collimation
 Object
 Attenuation
coefficient
 Source-object geometry
 Detector
 Object-detector
geometry
 Efficiency
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Advantages of Standard Diagnostic
Medical X-ray Imaging Systems
 Readily
available
 Reasonably cheap
 Simple systems to maintain
 Many experienced and trained
personnel due to the fact that
technology has existed for a while
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science
Disadvantages of Diagnostic
Medical X-ray Imaging Systems
 Exposure
to harmful radiation.
 Not much contrast between different
soft tissues.
 Image is a shadowgram (projection
image) with no depth information.
Imaging Science Fundamentals
Chester F. Carlson Center for Imaging Science