exposure

Card Set Information

Author:
nethers-1944
ID:
10605
Filename:
exposure
Updated:
2010-03-15 12:49:47
Tags:
rad exposure
Folders:

Description:
grids, screens etc
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  1. DQE
    detection quantum efficiency
    Percent of x-rays absorbed by screen
  2. CE
    conversion efficiency
    Light emitted for each x-ray absorbed
  3. screen layers
    • protective layer
    • phosphor - active layer (the thicker the more converted to light)
    • reflective layer
    • base
  4. Stimulus
    • outer shell electrons absorb some energy and raised to higher energy level
    • and creates a hole in the outer shell
  5. Phosphorescence
    • visible light emitted after stimulation stops
    • elec returns to normal after more than one revolution
  6. fluorescence
    • Visible light emitted only while the phosphor is stimulated
    • elec returns to normal in one revolution
  7. intensifying factor equation
    IF = exposure required without screens/ exposure required with screens
  8. speed is determined by
    • –Number of x-rays interacting with the phosphor
    • –Efficiency of conversion of x-ray energy into light
  9. dye is added to screens to:
    • –Added to control spread of light
    • –Improve spatial resolution, decrease speed
  10. noise
    • Appears on radiograph as speckled background
    • Occurs more with fast screens, high kvp
    • Noise reduces image contrast
  11. spatial resolution
    • ability to produce ACCURATE image
    • How small an object can be imaged
  12. contrast resolution
    ability to distinguish between similar tissues
  13. image detail
    determined by spatial resolution and contrast resolution
  14. faster screens
    • larger crystals
    • low spatial resolution
  15. front of screen
    low atomic number so xr aren't attenuated
  16. conversion efficiency
    • Amount of visible light emitted to xray energy absorbed
    • calcium tungstate about 5% of absorbed converted (amber safe light)
    • Rare earth absorbs about 15 –20% converted (red safe light)
  17. screen speed technique equation
    relative speed from/ relative speed to x mAs old = mAsnew
  18. grid ratio
    • The higher the strip and the smaller the interspace---the straighter the beam must be to get thru
    • The shorter the strip, or the wider the interspace, the more angled beam can get thru
  19. grid frequency
    • number of lead strips per inch
    • .. high freq requires higher tech and results in high pt dose
  20. disadvantages of air gap tech
    • -image magnification
    • -Loss of recorded detail
    • * so you have to use a longer SID
  21. bucky factor values from nongrid to 16:1
    • ng=1
    • 5=2
    • 6=3
    • 8=4
    • 10&12=5
    • 16=6
  22. wetting the image:
    • •Allows chemicals to reach the emulsion
    • •swells emulsion and causes it to expand
  23. developing agents
    • –hydroquinone acts slow and gives blacks
    • –phenidone acts fast and gives shades of gray
  24. preservative
    • controls oxidation in the developer
    • helps maintain proper development rate and keeps chemistry lasting longer
  25. 3 factors affecting developing
    • •Time
    • •temperature
    • •concentration of chemicals
    • all lead to inc development of crystals giving more density
  26. fixer:
    • •Stops action of developer
    • •neutralizes the alkaline
    • •acetic acid
  27. buffer
    helps maintain the ph
  28. 6 principle components of processing
    • •Transport
    • •temperature control
    • •circulation
    • •replenishment
    • •dryer
    • •electrical
  29. 3 types of rollers
    • transport rollers–1 inch
    • Master rollers–3 inch
    • planetary rollers
  30. Turnaround assembly
    • –master roller
    • –planetary roller
    • –guide shoe
  31. film layers
    • • supercoating
    • • emulsion
    • • adhesive layer
    • • Base
  32. 2 parts of the emulsion
    • –gelatin
    • –silver halide crystal
  33. speed of films depends on
    the thickness of emulsion=greater speed b/c more sensitive to light
  34. reciprocity law
    Exposure = intensity x time

    fails at very long and short times
  35. storage of film
    • 68 F up to one year
    • 40-60% humidity
    • no light
    • jeep away from rad
  36. factors affecting scatter
    • kvp
    • field size
    • pt thickness
  37. grid ratio formula
    height of grid/distance of interspace
  38. grid frequency
    10,000/ width of strip + width of interspace
  39. CIF
    contrast with grid/ contrast w.o grid
  40. Bucky Factor
    hit top/ hit bottom
  41. tech change for grids
    ratio of BF to/ ratio of BF from *mAs
  42. selectivity
    primary transmitted thru/scatter transmitted thru
  43. cut off
    SID/ grid ratio
  44. magnification factor
    • image size/ object size
    • or
    • SID/SOD
  45. noise components
    • film graininess
    • structure mottle
    • quantum mottle
    • scatter radiation
  46. shape distortion depends on:
    • object thickness
    • object position
    • object shape
  47. prevent shape distortion by:
    • part parallel to grid
    • CR perpendicular to part
    • CR perpendicular to IR
  48. if you angle the part what happens
    foreshortened
  49. angle the IR what happens
    elongation
  50. prevent size distortion by:
    • part close to IR
    • straight beam.. can make straighter by inc SID
  51. reduce magnification by using
    high SID and low OID

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