Diagnostic X-ray Imaging: Physics and Technology

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Diagnostic X-ray Imaging Physics and Technology

• Dr. Nabil Maalej

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Outline

• X-ray Production
• X-ray Interaction with Matter
• X-ray Damage to Tissue
• X-ray Image Detectors
• Major Advances in X-ray Imaging

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Discovery of X-rays

• In December 1895, German physicist Wilhelm
  Roentgen discovered these mysterious rays X-rays,
  with X standing for unknown. In recognition of
  his discovery, Roentgen in 1901 became the first
  Nobel laureate in physics.

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What are X-rays?

• They are an electromagnetic radiation emitted by
  charged particles interactions
• Photons which can penetrate through matter
• They have no mass or charge
• They travel at the speed of light
• Energy h? hc/?

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EM Spectrum
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X-ray Production
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Electron Striking High Z material
99 or more of electron Energy goes into heat
Electron
1 or less of electron Energy goes into X-rays
High Z Material
X-ray Photon
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Bremsstrahlung X-rays
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Bremsstrahlung Spectrum
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Characteristic X-rays
Ejected Electron
Electron
Rebounding Electron
Characteristic X-ray
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X-ray Spectrum
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X- ray spectrum
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Outline

• X-ray Production
• X-ray Interaction with Matter
• Photoelectric
• Compton Scattering
• Pair Production
• Rayleigh scattering
• X-ray Damage to Tissue
• X-ray Image Detectors
• Major Advances in X-ray Imaging

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Photoelectric Interaction
T
h?
h? T BEelectron
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Compton Scattering
T
h?
h?
h? T BEelectron h?
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Pair Production
h?1
T
h?2
h?
T-
h? 2m0c2 TT?
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Rayleigh (Coherent) Scattering
h?
h?
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X- ray Interactions
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Importance of Different Interactions
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Total Interaction Cross Section

• Three relevant interaction processes with
  individual atomic cross-sections
• Photoelectric absorption (a?)
• Compton scattering (a?)
• Pair production (a?)
• Total atomic cross section a?T a? a? a?

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Linear Attenuation Coefficient

• The linear attenuation coefficient ? /cm is
  the probability of interaction per unit length

• ? mass density g/cm 3
• NA 6.02....1023 1/mol (Avogadros number)
• A Atomic Weight g/mol
• a?T Total atomic cross section cm2

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Attenuation of X-ray Intensity (Narrow Beam
Geometry)

• I is the radiation intensity after traversing a
  thickness x
• Io is the original radiation intensity
• µ is the linear attenuation coefficient (cm-1)
• x is the thickness of attenuating material (cm)

I Io e (- µ x)
Io
x
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Attenuation Coefficients
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Outline

• X-ray Production
• X-ray Interaction with Matter
• X-ray Damage to Tissue
• X-ray Image Detectors
• Major Advances in X-ray Imaging

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Damage to DNA
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Damage to DNA

• Direct damage to DNA molecule
• Indirect damage to DNA by Ionisation of water and
  the release of free radicals
• H20 ? H20 e-
• H20 ? H OH (free radical)
• OH OH ? H2O2 (Hydrogen peroxide)
• Release of H2O2 ? DNA damage

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Biological Effects
Stage Timescale Effect
Initial Physical Interaction 10-17-10-15s Ionization and Excitations
Chemical 10-14-10-3s Creation of free radicals excited molecules yielding biologically harmful products
Bio-molecular Sec - Hours Damage to DNA, proteins, nucleic acids, etc.
Biological Hours-Decades Cell damage, death, mutations
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Estimated Risk of Cancer
X-ray examination Estimated risk of fatal cancer
Dental intra-oral 1 in 2 000 000
Chest 1 in 1 000 000
Barium meal 1 in 6 700
CT head 1 in 10 000
CT chest 1 in 2 500
Car Accident 1 in 10 000
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Outline

• X-ray Production
• X-ray Interaction with Matter
• X-ray Damage to Tissue
• X-ray Image Detectors
• Film
• Film-Screen Combination
• Image Intensifier
• Flat Panel Detectors
• Major Advances in X-ray Imaging

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X-ray Film
(1-5 ?m)
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Film Characteristic
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Screen-Film Combination
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Image Intensifier
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Flat Panel Image Receptor
Active Matrix Array sizes of up to 40 cm x 40 cm
containing up to 9 million pixels
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Direct Image Receptors
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Film Vs. Flat panel Image
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Film Vs. Flat Panel Detector
Linearity for the flat panel detector and x-ray
film. The X-ray film has a non-linear response
and is limited in dynamic range.
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Outline

• X-ray Production
• X-ray Interaction with Matter
• X-ray Damage to Tissue
• X-ray Image Detectors
• Major Advances in X-ray Imaging

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X-ray Radiography Machine
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X-ray Images
Chest X-ray
Head X-ray
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Fluoroscopy

• Enables radiologists to visualize X-ray images in
  real time on a television monitor. In most
  instances the procedure would involve the
  administration of some form of 'contrast' agent
  to outline the region of interest

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Fluoroscopy Images
Barium Used to Visualize Intestines
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Mammography

• A mammography machine is an X-ray machine
  dedicated to breast images. Compared with
  conventional X-ray techniques, mammograms are
  obtained with much lower energy X-rays of around
  20,000 volts.

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Digital Angiography
It is a diagnostic procedure that produces X-ray
pictures of blood vessels. A catheter is inserted
in the vessel to inject contrast fluid into the
lumen of the blood vessel, which then becomes
visible on X-ray images.
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Digital Angiography Images
First Angiogram(1896, Hankel) Mercury was
injected in a post mortem hand
Digital Subtraction Angiography (Mistretta, 1980s)
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Digital Angiography Images
3-D Angiogram of The Brain Arteries
Angiogram of The Coronary Arteries
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Computerized Tomography (CT)

• The technique of CT scanning was developed in
  1973 by Hounsfield. A thin fan beam of X-rays
  generated by a conventional X-ray tube passes
  through a single 'slice' of a patient through to
  a bank of X-ray detectors.

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Principle of Image Reconstruction
I0
?y
?x
I1 I0e-(ß1ß2)?x
ß1
ß2
I0
I2 I0e-(ß3ß4)?x
ß3
ß4
I4 I0e-(ß2ß4)?y
I3 I0e-(ß1ß3)?y
4 equations solved for 4 unknown ß
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CT Image Reconstruction
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CT Machine
CT Machine Rotating Parts
CT Machine
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Helical CT
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CT 3-D Images
3-D CT Image of the Head
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X-Ray Historical Events

• 1895 Roentgen discover X-ray
• 1896 First medical application of x-rays in
  diagnosis
• 1913 The Coolidge hot-filament x-ray is
  developed
• 1929 The rotating anode tube is introduced
• 1948 Coltman develops the first fluoroscopic
  image intensifier
• 1973 Hounsfield completes the development of the
  first CT imager
• 1979 Mistretta demonstrates digital fluoroscopy
• 1982 Toshiba introduces the Spiral CT
• 1996 Direct digital radiography is developed
  (thin film transistors)
• 2000 GE introduces the first direct digital
  mammography imaging

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Thank You