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Medical Image Analysis
Medical Imaging Modalities: X-Ray Imaging
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

Anatomical or structural
◦ X-ray radiology, X-ray mammography, X-ray
CT, ultrasound, Magnetic Resonance Imaging

Functional or metabolic
◦ Functional MRI, (Single Photon Emission
Computed Tomography) SPECT, (Positron
Emission Tomography) PET, fluorescence
imaging
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray Imaging

Conrad Roentgen
◦ Discovered X rays
in 1895
◦ Received the
Nobel Prize in
1901
Figure comes from the Wikipedia, www.wikipedia.org.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

Soft X rays
◦ Wavelengths from 10 nm to 0.1 nm,
corresponding to 120eV to 12.3 KeV

Hard X rays
◦ Wavelengths shorter than 0.1 nm up to 0.001
nm

Diagnostic
◦ 12.3 KeV to 123 KeV
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-Ray Generation

Principle
◦ An accelerated electron loses energy in
interaction with an atom and the loss of
energy emits X-ray photons in a scattered
direction
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Ejected
Electron
39 P
50N
K
L
N
O
X-ray
Photon
Incident
Electron
Figure 4.1. Atomic structure of a tungsten atom. An incident electron with
energy greater than K-shell binding energy is shown interacting with a K-shell
electron for the emission of an X-ray photon.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

Tungsten
◦ K-shell binding energy level: 69.5 keV
◦ L-shell binding energy level: 10.2 keV
◦ An emission of X-ray photon of 59.3 keV

X-ray generation
◦ Electrons are released by the source cathode
and are accelerated toward the target anode
in a vacuum under the potential difference
ranging from 20,000 to 150,000 volts
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure comes from the Wikipedia, www.wikipedia.org.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure comes from the Wikipedia, www.wikipedia.org.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

White radiation

Also called Bremsstrahlung radiation
spectrum
Figure comes from the Wikipedia, www.wikipedia.org.

An X-rat generation tube with rotating
anode
Figure comes from the Wikipedia, www.wikipedia.org.
Figure comes from the Wikipedia, www.wikipedia.org.
X-ray 2-D Projection Imaging

Diagnostic radiology
◦ 2-D projection of the three-dimensional
anatomical structure of the human body
◦ Localized sum of attenuation coefficients of
material: air, blood, tissue, bone
◦ Film or 2-D array of detectors

Digital radiographic system
◦ Use scintillation crystals optically coupled
with photomultiplier
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray Source
3-D Object or
Patient
Anti-scatter Grid
X-ray Screen
Film
X-ray Screen
2-D Projection
Image
Figure 4.2. (a). A schematic diagram of a 2-D X-ray film-screen radiography
system. A 2-D projection image of the 3-D object is shown at the bottom. (b).
X-ray radiographic image of a normal male chest.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray 2-D Projection Imaging

Scattering
◦ Create artifacts and artificial structures

Reduce scattering
◦ Anti-scattered grids and collimators

X-ray intensifying screen
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray Mammography

Target material
◦ Molybdenum: K-, L-, M-shell binding energies
levels are 20, 2.8, 0.5 keV. The characteristic
X-ray radiation is around 17 keV.
◦ Phodium: K-, L-, M-shell binding energies levels
are 23, 3.4, 0.6 keV. The characteristic X-ray
radiation is around 20 keV.

A small focal spot of the order of 0.1mm
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray Source
Compression
Device
Compressed
Breast
Moving
Anti-scatter Grid
X-ray Screen
Film
X-ray Screen
Figure 4.3. A film-screen X-ray mammography imaging system.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure 4.4. X-ray film-screen mammography image of a normal
breast.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

Normal (left) versus cancerous (right)
Figure comes from the Wikipedia, www.wikipedia.org.
X-ray Computed Tomography

3-D
I out ( y; x, z )  I in ( y; x, z )e 
  ( x , y , z ) dx
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure comes from the Wikipedia, www.wikipedia.org.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
y
x
z
X-Y Slices
Figure 4.5. 3-D object representation as a stack of 2-D x-y slices.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
y
x
(x,y; z)
15
z
12
Iin(x; y,z)
22
42
52
62
72
82
92
Iout(x; y,z)
11
Figure 4.6. Source-Detector pair based translation method to scan a
selected 2-D slice of a 3-D object to give a projection along the y-direction.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure 4.7: The translate-rotate parallel-beam geometry of first generation
CT scanners.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
X-ray Computed Tomography

Generations
◦ First: an X-ray source-detector pair that was
translated in parallel-beam geometry
◦ Second: a fan-beam geometry with a
divergent X-ray source and a linear array of
detectors. Use translation to cover the
object and rotation to obtain additional views
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.

Generations
◦ Third: a fan-beam geometry with a divergent
X-ray source and an arc of detectors.
Without translation. Additional views are
obtained by simultaneous rotation of the Xray source and detector assembly. “Rotate
only”
◦ Fourth: use a detector ring around the
object. The X-ray source provides a divergent
fan-beam of radiation to cover the object
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure 4.8. The first generation X-ray CT scanner
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Ring of Detectors
Source
Rotation Path
Source
X-rays
Object
Figure 4.9. The fourth generation X-ray CT scanner geometry.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure 4.10. X-ray CT image of a selected slice of cardiac cavity of a
cadaver.
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Figure 4.11. The pathological image of the selected slice shown with the Xray CT image in Figure 4.10
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.
Spiral X-ray CT

Spiral CT
◦ The patient bed is moved at a constant speed
◦ The gantry is rotated within the circular
opening
◦ Provide the data along a spiral or helical path
◦ Pitch:
 t : slice thickness
 d : the movement of bed one complete ratation (360
degrees) of gantry
d
p
t
Contrast Agent, Spatial Resolution,
and SNR

Contrast agent
◦ Barium sulfate, to enhance contrast in upper
gastrointestinal (GI) tract imaging
◦ Barium atom has a K-edge at 37.4KeV
◦ Iodine-based, used in angiography, urography,
and intra-arterial DSA to improve visibility of
arteries and blood vessels
◦ Iodine has a K-edge at 33.2KeV
Figures come from the textbook: Medical Image Analysis, Second Edition,
by Atam P. Dhawan, IEEE Press, 2011.