*X-ray Definitions

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Author:
sirius
ID:
177590
Filename:
*X-ray Definitions
Updated:
2012-10-14 23:22:55
Tags:
Xray Definitions
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NBCE 2
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  1. Density (Film)
    Density is directly related to the quantity of x-rays produced (mAS)
  2. Contrast (radiographic)
    Different densities (black and white). High contrast (short scale) very white and very black; low contrast (long scale) more shades of gray.  
  3. What is contrast inversely related to?
    kVp
  4. What happens to contrast kV is increased?
    Decrease contrast/ more grays
  5. What happens to contrast kV is decreased?
    Increased contrast/ more black and white
  6. What do geometric factors include?
    • Focal spot size
    • FFD
    • OFD
    • xray machine alignment
    • patient placement
  7. Distortion
    Misrepresentation of the size or shape of an object.
  8. Detail
    Degree of film sharpness
  9. How do you improve detail?
    • Smaller focal spot
    • Collimation
    • Increase FFD
    • Decreased OFD
    • grids
    • patient positioning
    • machine alignment
    • shorter exposure time
  10. Penumbra
    Area of unsharpness or fuzziness
  11. What happens when penumbra is increased?
    • Larger focal spot size
    • lack of collimation
    • decrease FFD
    • increase OFD
  12. Primary radiation
    The purpose of exposing the film (the useful beam). 
  13. * Scatter radiation
    Secondary radiation produced by an absorber (body), produced film fog.
  14. FFD Focal Film Distance
    (Also TFD, SID, SFD) Distance between the focal spot and the film. 
  15. If you increase FFD what happens?
    Decreases magnification
  16. OFD Object Film Distance
    Always decrease as much that is practical to decrease magnification.
  17. Inverse square law
    The intensity of the radiation varies inversely with the square of the distance. 
  18. Inverse square law: what happens if you double the distance (FFD)?
    Decrease of intensity of the radiation to 1/4 and requires a compensatory increase of the mAs by 4x's.
  19. Anode heel effect
    • Due to the angle (bevel) intensity.
    • INCREASES slowly towards CATHODE; and DECREASES rapidly towards the ANODE.
  20. Air gap technique
    Reducing scatter radiation. between 10-15cm from the film.
  21. What is the disadvantage of the air gap technique?
    increases magnification
  22. Rectification
    converting AC current to DC current
  23. 15% Rule
    Increase kVp by 15% double the mAs.
  24. Wolff's Law
    Bone deposition occurs along the lines of increased mechanical stress.
  25. Hueter-volkmann Law
    Pressure on a growth plate retards the rate of growth, traction accelerates.

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