Card Set Information

2014-02-02 17:47:00

Show Answers:

  1. what are intensifying screens used for
    used to amplify the incoming xray beam and reduce patient dose
  2. when intensifying screens are struck by xray beams what do the produce
    large amounts of light photons
  3. what is 99 percent of the latent image produced by
    light photons created by the intensifying screens and only 1% is contributed to actual xray photons striking the film
  4. what are the film screen speeds for no screen film/screen 50 f/s 100 f/s 200 f/s 300 f/s
    • film/screen = .05
    • 50 f/s = .5
    • 100f/s = 1
    • 200f/s = 2
    • 300f/s = 3
  5. what is the non screen called
    cardboard holder
  6. what is the basic function of the screen
    to produce light
  7. what is the construction of the screen
    screens are composed of radiolucent plastic coated with phosphors that will emit light when struck by xray photons
  8. what is the active layer of intensifying screens
    phosphors that emit light
  9. list all the layers of an intensifying screen
    • base
    • reflective layer
    • phosphor layer
    • protective coat
  10. what is the base made out of
    polyester plastic
  11. what is spectral matching
    when intensifying light matches emitting light from the film
  12. what is the reflective layer
    what is it used for?
    is a layer of magnesium oxide or titanium dioxide used to reflect the light towards the film
  13. what happens when a phosphor is struck by light
    it emits light isotropically, so when a reflective layer is added to nearly twice as much light is reflected toward the film
  14. what film has a better result in detail no screen on film or film w/ intensifying screen
    a film with no screen because it has less layers to go through but there is in increase of patient dose
  15. what are phosphors
    materials that are capable of absorbing the energy of an incident xray photon and the emitting light photons
  16. what layer is applied on top of the phosphor layer
    what is its function
    • protective coat
    • protects from abrasion and stain during loading and unloading cassette
  17. what are the four characteristics of phosphors
    • high atomic number (allow for more photoelectric interactions)
    • high conversion efficiency (xrays to light)
    • appropriate spectral matching (not sensitive to red)
    • minimal phosphoresence (over emission of light)
  18. what is conversion efficiency
    ability of phosphor to emit as much light per xray photon interaction as much as possible is a measurement of film screen speed
  19. what is spectral emission
    an indication of the precise wavelength emitted by the phosphor
  20. what is spectral matching
    the spectral emission must match the sensitivity of the film to ensure maximum latent image formation
  21. what is luminescence
    is the ability of a material to emit light in response to excitation
  22. what are the two types of luminescence
    fluorescence and phosphorescence
  23. what is fluorescence and phosphorescence
    is instantaneous and phosphorescence is delayed emission
  24. what is desirable in regards to fluorescence
    maximum fluorescence and minimal phosphorescence are desirable
  25. delayed phosphorescence is aka
    screen lag or afterglow
  26. what is the normal life span of an intensifying screen
    5-7 years
  27. what is the best type of phosphors used in intensifying screens
    rare earths phosphors
  28. why are rare earth phosphors best
    2 reasons
    because their greater absorption abilities, intensification factors and conversion efficiency

    they offer increased speed with maintaining resolution when compared to similar calcium tungstate screens
  29. what is the conversion efficiency percentage of rare earth phosphors
    15-20% which is good
  30. what is the difference between calcium tungstate and tungsten
    calcium tungstate is phosphor and tungsten is a metal
  31. what is the conversion efficiency of the calcium tungstate
  32. list examples of rare earth phosphors
    • gadolinium
    • lanthanum
    • yttrium
  33. what is the k-edge energy of calcium tungstate
    what color does it emit
    • 70
    • blue light
  34. what is orthochromatic and panchromatic
    • orthochromatic is films are not sensitive to the red spectrum
    • panchromatic films are sensitive to all colors
  35. what happens if the film and screen are not spectrally matched
    its conversion efficiency will be greatly reduced
  36. what is resolution
    the ability to accurately image an object
  37. small crystals and thinner phosphor layer have increased resolution but what speed
    slow speed
  38. what is the naked eye measurement of the lines pairs measurement
  39. what is line pairs/mm
    minimum size and space between objects that can be visualized
  40. what is line spread function
    ability of the system to accurately represent borders of object
  41. what is Modulation transfer function
    recorded detail/availabel detail used in CR and DR
  42. what is the most common problem screen resolution
    poor film/screen contact
  43. what is the result of poor film screen contact
    increases image density
  44. how do we test for poor film screen contact
    using wire mesh test
  45. how do we decrease quantum mottle
    increasing mAs
  46. what is another name for quantum mottle
    radiographic noise it is where the radiograph looks very grainy and blotchy
  47. how does quantum mottle occur
    when insufficient phosphor crystals emit light to expose a coherent expanse of film the resulting image will appear grainy which is caused by an insufficient quantity of photons striking the screen
  48. at what temperature will cause a decrease in speed
    over 100 degrees in outdoor radiography
  49. what other factor increases speed
    increase of kvp
  50. what determines screen speed and sensitivity
    phosphor size, concentration and layer thickness determines speed
  51. large phosphor has what type of speed
    fast speed reduced resolution
  52. what is the most useful rating of an intensifying screen
    relative speed
  53. what are the three screen speed classifications
    • intensification factor
    • descriptive rating
    • relative speed number
  54. what back part of the cassette is used to reduce the residual beam and reduce back scatter
    lead foil
  55. what do we need for good screen film contact
    foam inside
  56. what is a white spot and what is considered as
    it is a low density spot and considered as an artifact
  57. how should cassettes be stored
    how on the tops
    what should we never do to a cassette
    • on end like a book and empty of film
    • tops should never be fully opened
    • never close a wet cassette
    • cleaned with electrostatic solution