DI – general

1. Diagnostic Imaging

2. Physics

xray tube

  • current through cathode filament generates e-
  • voltage difference at anode target attracts e-  
  • radiative interactions of electrons with tungsten atoms:
  • characteristic radiation – collisional interaction (electrons collide and release energy as xray)
  • bremsstrahlung – braking interaction (electron orbits nucleus, releasing energy)

film/screen radiography

  • exposure = blackness
  • increases with either # or energy of photons
  • contrast
  • increase mAs; high contrast (more photoelectric interactions)
  • increase kVp; low contrast (more compton interactions)
  • grid: to decrease scatter fuzz from thick patient structures; increase mAs 2-3x
  • intensifying screens: converts xray photon to multiple visible light photons; spare mAs
  • film: exposed by light photons from intensifying screen
  • spatial resolution: film is #1 (b/c no pixels?)

3. Digital Radiography

direct-readout electronic x-ray detectors (DX): no cassette; use either direct or indirect technique to convert xrays into electric charge

exposure latitude: the extent to which a plate (film, image plate, or flat panel) can be over- or underexposed and still achieve an acceptable result.

4. MRI & CTI

5. Interpretation

  • opacities
  • metal > bone > fluid/soft tissue > fat > air
  • geometry
  • magnification
  • superimposition: something that is not even part of a structure looks like a lesion
  • summation “shadow”: overlapping opacities stack
  • silhouette: the lack of a silhouette, because surrouded by tissue of the same opacity
  • to xrays, fluid and soft tissue are the same
  • standardization
  • roentgen signs (describing abnormalities)
  • size – shape – number – location – margination – opacity

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