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Medical Xray Imaging System

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This is called the 'wave-particle duality' of EMR. Gamma Rays. Ultraviolet Rays. X Rays ... wavelength, the distance between two identical points on a wave. ... – PowerPoint PPT presentation

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Title: Medical Xray Imaging System


1
Medical X-ray Imaging System
  • Imaging Science Fundamentals

2
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.

3
Typical Imaging Chain forMedical X-ray Systems
X-ray source
Film
Object
Image
Collimator
4
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.

5
Wavelength
?
  • ??(lambda) is called wavelength, the distance
    between two identical points on a wave.

6
Frequency
time
unit of time
  • ??(nu) is called frequency, the number of cycles
    per unit of time.
  • It is inversely proportional to the wavelength.

7
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
8
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)
9
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.

10
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.

11
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

12
Attenuation Coefficient
5
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.
13
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)

14
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.

15
Typical X-Ray Images
X-ray image of hand
Dental X-ray
Mammogram
16
Image Quality Factors
  • Source
  • Energy of the photons
  • Collimation
  • Object
  • Attenuation coefficient
  • Source-object geometry
  • Detector
  • Object-detector geometry
  • Efficiency

17
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

18
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.
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