Medical Image Analysis Medical Imaging Modalities: X-Ray Imaging Figures come from the textbook: Medical Image Analysis, Second Edition, by Atam P. Dhawan,

Medical Image AnalysisMedical Image AnalysisMedical 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


X-ray ImagingX-ray Imaging


Figure comes from the Wikipedia, www.wikipedia.org.

Conrad Roentgen◦Discovered X

rays in 1895◦Received the

Nobel Prize in 1901

Soft X rays◦Wavelengths from 10 nm to 0.1 nm,

corresponding to 120eV to 12.3 KeVHard X rays

◦Wavelengths shorter than 0.1 nm up to 0.001 nm

Diagnostic◦12.3 KeV to 123 KeV


X-Ray GenerationX-Ray GenerationPrinciple

◦An accelerated electron loses energy in interaction with an atom and the loss of energy emits X-ray photons in a scattered direction



39 P50N K

LO

N

Ejected Electron

Incident Electron

X-ray Photon

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.

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

keVX-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







White radiationAlso called Bremsstrahlung

radiation spectrum

An X-rat generation tube with rotating anode



X-ray 2-D Projection X-ray 2-D Projection ImagingImagingDiagnostic 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 detectorsDigital radiographic system

◦Use scintillation crystals optically coupled with photomultiplier



X-ray Source

X-ray ScreenFilmX-ray Screen

3-D Object orPatient

2-D ProjectionImage

Anti-scatter Grid

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.


X-ray 2-D Projection X-ray 2-D Projection ImagingImagingScattering

◦Create artifacts and artificial structures

Reduce scattering◦Anti-scattered grids and collimators

X-ray intensifying screen


X-ray MammographyX-ray MammographyTarget 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



X-ray Source

X-ray ScreenFilmX-ray Screen

CompressedBreast

MovingAnti-scatter Grid

CompressionDevice

Figure 4.3. A film-screen X-ray mammography imaging system.


Figure 4.4. X-ray film-screen mammography image of a normal breast.

Normal (left) versus cancerous (right)


X-ray Computed X-ray Computed TomographyTomography3-D


dxzyx

inout ezxyIzxyI),,(

),;(),;(




y

x

zX-Y Slices

Figure 4.5. 3-D object representation as a stack of 2-D x-y slices.


x

z

y

Iin(x; y,z)Iout(x; y,z)

(x,y; z)

11

22 92

15

12 42 52 62 72 82

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.


Figure 4.7: The translate-rotate parallel-beam geometry of first generation CT scanners.

X-ray Computed X-ray Computed TomographyTomographyGenerations

◦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


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 X-ray 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



Figure 4.8. The first generation X-ray CT scanner


Ring of Detectors

Source

SourceRotation Path

X-rays

Object

Figure 4.9. The fourth generation X-ray CT scanner geometry.


Figure 4.10. X-ray CT image of a selected slice of cardiac cavity of a cadaver.


Figure 4.11. The pathological image of the selected slice shown with the X-ray CT image in Figure 4.10

Spiral X-ray CTSpiral X-ray CTSpiral 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: : slice thickness : the movement of bed one complete

ratation (360 degrees) of gantryt

dp

td

Contrast Agent, Spatial Contrast Agent, Spatial Resolution, and SNRResolution, and SNRContrast 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


Medical Image Analysis Medical Imaging Modalities: X-Ray Imaging Figures come from the textbook: Medical Image Analysis, Second Edition, by Atam P. Dhawan,

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