Medical Xray Imaging System

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Medical X-ray Imaging System

• Imaging Science Fundamentals

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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.

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Typical Imaging Chain forMedical X-ray Systems
X-ray source
Film
Object
Image
Collimator
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Electromagnetic Radiation
Ultraviolet Rays
Infrared (IR)
Radio wave
Gamma Rays
Microwave
X Rays
Light

• EM radiation can be thought of as oscillating
  electric field which generates oscillating
  magnetic field which generates oscillating
  electric fieldand 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.

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Wavelength
?

• ??(lambda) is called wavelength, the distance
  between two identical points on a wave.

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Frequency
time
unit of time

• ??(nu) is called frequency, the number of cycles
  per unit of time.
• It is inversely proportional to the wavelength.

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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
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Photons review

• Photons are little packets of energy.
• Each photons energy is proportional to its
  frequency.
• A photons energy is represented by h?

E h?
Energy (Plancks constant) x (frequency of
photon)
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X-Rays
Ultraviolet Rays
Infrared (IR)
Gamma Rays
Radio wave
Microwave
X Rays
Light
10-9 m (1 nm)
10-11 m (0.01 nm)
soft
hard

• Usually detected as particles of energy
  (photons).
• Discovered in 1895 by Wilhelm Conrad Roentgen.

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X-Ray Production
Cathode(-)
e-
e-
h?
h?
Anode ()

• Electrons are accelerated from cathode to anode.
• When high energy electrons hit atoms of heavy
  metals, the atoms produce X-ray photons.

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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

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Attenuation Coefficient
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Attenuation Coefficient
1
0.1
10
50
100
150
500
Photon Energy (keV)
Attenuation coefficients tell you the x-ray
blocking power of a material.
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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)

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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.

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Typical X-Ray Images
X-ray image of hand
Dental X-ray
Mammogram
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Image Quality Factors

• Source
• Energy of the photons
• Collimation
• Object
• Attenuation coefficient
• Source-object geometry
• Detector
• Object-detector geometry
• Efficiency

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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

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Disadvantages of DiagnosticMedical 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.