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Week 7 Medical Imaging (types (x-ray (methods (principle (high energy…

- - - - scintillator
    - - principle
        
        high energy electon
        
        strips atom of electron in low energy shell
        
        electron in high energy shell drops to fill the void, releasing X-ray
        
        specific energies are released in this way (k-lines)
      - bremsstrahlung
        
        anode contains heavy element
        
        as electrons pass into anode, it is decelerated or change direction
        
        results in release of kinetic energy as radiation
        
        results in release of heat
      - control
        
        voltage
        
        maximum energy of x-rays
        
        affect contrast
        
        affect attenuation and dose(absorption)
        
        current
        
        intensity
        
        brightness
        
        dose
        
        spot size(where the electrons hit the anode)
        
        affects spatial resolution and image sharpness
        
        small
        
        sharper
        
        heavy heat loading
        
        solution
        
        rotating anode
    - - lens & mirror
      - fibre-optic taper (demagnification)
    - - attenuation coefficient
      - when AC is not adequate for contrast
        
        add a contrast agent to increase contrast (angiography)
    - - x-ray image from different angles, then reconstruct
  - - - energy from the pulse is reflected off interfaces between materials
      - echo are detected by the transceiver
      - time taken for the echo to return gives the depth of the interface
      - strength tells the various material
      - frequency shift tells the speed of the material
    - - solution
        
        special ultrasound gel to provide transmission into the body
    - - attenuation coefficient path length frequency
        
        higher frequency
        
        high attenuation
        
        low penetration
        
        high spatial resolution
        
        high penetration
        
        high power
        
        low frequency