Dmi 100 Review image evaluation

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Dmi 100 Review image evaluation
2012-11-24 12:43:27
density grids filters SID OID mAs kVp intensifying screen film developer curve AEC artifacts

image evaluation
Show Answers:

  1. what is density?
    amount of blackness on a given area of a radiograph
  2. how do you calculate density?
  3. what is light incident?
    light striking the radiograph from the back, coming from the view box
  4. what is light transmitted?
    light that is seen coming through the radiograph whilte it is being viewed by either the human eye or a densitometer
  5. how is optical density made visible?
    when the crystals in the film's emulsion are converted to black metallic silver in the developer solution
  6. what is the reciprocity law?
    any combination of mA and time that produce the same mAs value will result in the same density on the radiography
  7. what relationship does mAs have with density?
    direct proportional
  8. how does kVp affect density?
    directly affects it, although not in a directly proportional relationship
  9. what is the 15% rule?
    an increase in kVp of 15% will double the density
  10. what is inverse square law?
    the intensity of the x-ray beam is inversely proportional to the square of the distance between the source of x-rays and the image receptor

  11. what is the density maintenance formula?
  12. what type of relationship does film-screen combination have with density?
    • direct proportion
    • as speed (sensitivity) increases, density increases
  13. What do grids accomplish?
    • decrease the amount of scatter radiation striking the image receptor
    • decreases density unless is increased to compensate
  14. what do beam restriction devices do to density?
    decrease density by limiting the size of the x-ray beam unleass mAs is increased to compensate
  15. what does filtration do to the density?
    • negligible effect on density
    • for radiation protection
    • reduces soft, long wavelength rays
  16. what is contrast?
    differences in adjacent densities on a radiograph
  17. how do grids affect contrast?
    less scatter = fewer gray tones = higher contrast
  18. how does beam restriction affect contrast?
    less radiation = less scatter = fewer gray tones = higher contrast
  19. how does filtration affect contrast?
    decreases small wavelength x-rays = stronger beam = increase scatter = more gray tones = decrease contrast
  20. what is subject contrast?
    patient's body controlling contrast
  21. what are the three controlling factors for subject contrast?
    • atomic number
    • tissue density
    • tissue thickness
  22. what are the factors that affect recorded detail?
    • OID
    • SID
    • Focal spot size
    • Film-Screen combo
    • Motion
  23. what are the two type of shape distortion?
    • size
    • shape
  24. what are the different parts of film?
    • protective coat
    • emulsion (active layer)
    • adhesive
    • base
  25. what is the base of the film made out of?
  26. what is the anatomy of a double emulsion film?
    • super coat
    • emulsion
    • adhesive
    • base
    • adhesive
    • emulsion
    • super coat
  27. what does the emulsion of a film contain?
    silver halide crystals suspended in gelatin
  28. what are the sensitive specks on silver halide crystals for?
    serve as centers for making the latent image visible
  29. what is the latent image?
    image contained in the silver halide crystals after exposure but beforew development
  30. what determines the speed of a film?
    • size of silver halide crystals
    • number of silver halide crystals
    • thickness of emulsion
    • (the larger the crystals and the thicker the emulsion, the faster the film)
  31. how does the speed of the film affect contrast?
    the faster the film the higher the contrast
  32. what determines the latitude of a film?
    • depends of the inherent contrast
    • the lower the inherent contrast the wider the latitude
  33. what are the other names for H&D curves?
    • sensitometric curves
    • characteristic curves
    • D log E curves
  34. what is plotted on a H & D curve?
    • x-axis: exposure
    • y-axis: density
  35. what does the toe portion of the H & D curve represent?
    • low exposure
    • low density
  36. what does the toe portion of the H&D curve also called
    base plus fog
  37. what does the body portion of the H&D curve also called
    • straight line portion
    • gamma
    • slope
  38. what does the body portion of the H & D curve represent?
    • measures usable densities
    • indicates overall gray scale of the film
  39. what does the shoulder portion of the H & D curve represent?
    • maximum density
    • blackest portion
  40. how do you determine the speed of a film by looking at the H&D curve?
    the closer the curve to the y-axis the faster the speed
  41. how do you determine the conrast of a film by looking at the H&D curve?
    • the steeper the slope of the curve the higher the contrast
    • the shallower the slope the lower the contrast
  42. how do you determine the recorded detail of a film by looking at the H&D curve?
    • based on the speed of the film
    • the faster the speed, the poorer the recorded detail
  43. what is the safe temperature for storing film?
    no greater than 68 to 78 degrees
  44. how much humidity is safe to store film?
    40 to 60%
  45. what causes the crinkle or half-moon marks on film?
    bending film over fingernail during handling
  46. what are the different parts of an intensifying screen?
    • protective layer
    • phosphor layer
    • reflective layer
    • base
  47. what determines the speed of an intensifying screen?
    • phosphor used
    • phosphor size (larger = faster)
    • active layer thickness (thicker = faster)
    • efficiency of reflective layer (higher = faster)
    • kvp used (higher = faster)
    • prescene of yellow dye in active layer (dye absorbs light)
    • conversion effciency of  phosphors
  48. what controls what in a film-screen combination?
    • speed controlled by screen
    • contrast controlled by film
  49. how many intensifying screens are used with a single emulsion film? how many for double emulsion film?
    • single = one intensifying screen
    • double = two intensifying screens
  50. what is the intensification factor?
    • ratio of exposure in mAs needed to produce image without screens compared with exposure in mAs needed to produce image with screens
  51. how is film-screen contact tested?
    by radiographing a wide-mesh screen
  52. what does a grid accomplish?
    reduces amount of scatter radiation reaching the image receptor
  53. when is a grid used?
    • when part thickness is 10 cm or greater
    • 70 kvp or higher
  54. how is a grid constructed?
    lead strips separated by aluminum interspacers
  55. what is grid ratio?
    • height of lead strips divided by the distance between them
    • grid ratio = H/D
  56. what is grid frequency?
    • number of lead strips per inch or cm
    • lines per inch or lines per cm
  57. what happens to the lead strip thickness when grid frequency increases?
    • decreases
    • becomes less visible
  58. what are the different types of grids?
    • linear
    • focused
    • crossed
  59. what is a linear grid?
    • lead strips are parallel to one another
    • x-ray tube may be angled along the length of the grid w/o cutoff
    • used primarily with large SID or small field
  60. what is a focused grid?
    • lead strips are angled to conincide with divergence of beam
    • used with specific ranges of SID
  61. what is grid radius?
    • distance at which focused grid may be used
    • also called focal distance or focal range
  62. what is a crossed grid?
    • consist of two linear grids placed perpendicular to each other
    • superior scatter cleanup
    • allow no angulation of x-ray beam
    • require perfect positioning and centering
    • primary use is biplane cerebral angiography
  63. what is contrast improvement factor?
    • measure of a grid's ability to increase contrast
    • ratio of the contrast with a grid to the contrast without a grid
  64. what is grid selectivity?
    ratio of primary radiation transmitted through the grid to secondary radiation transmitted through the grid
  65. what happens to selectivity when the grid frequency and grid ratio are high?
    more selectivity
  66. what does high selectivity mean?
    indicates high efficiency of scatter cleanup
  67. what is grid conversion factor?
    amount of exposure increase necessary to compensate for the absorption of image forming rays and scatter in the cleanup process
  68. what are the grid conversion factors?
    • 5:1 - 3
    • 8:1 - 4
    • 12:1 - 5
    • 16:1 - 6
  69. upside down focused grids will produce what type of grid error?
    normal density in the middle with decreased density on the sides
  70. off level focused grids will produce what type of grid error?
    decreased density over the entire image
  71. lateral decentering of focused grids will produce what type of grid error?
    cutoff visible to one side of the image
  72. focused grid decentering will produce what type of grid error?
    normal density in the middle with cutoff visible on the sides
  73. air gap technique is similar to what grid ratio?
  74. what does a grid do to contrast?
    increases contrast because it absorbs scatter radiation which decreases the amount of gray tones
  75. each step on the density control for AEC represents how much change in density?
  76. what does the developer do during processing of film?
    • converts exposed silver halide (bromide) crystals to black metallic silver
    • or convert latent image to manifest image
  77. what are the different types of agents in the developer?
    • reducing agents
    • activator
    • hardener
    • restrainer
    • preservative
    • solvent
  78. what are the reducing agents and what do they accomplish?
    • phenidone- quickly build gray tones
    • hydroquinone- slowly fill in black tones
  79. what does an activator do during processing?
    soften and swells film emulsion
  80. what does a hardener do?
    controls swelling of film emulsion to allow safe transport through the processor
  81. what does a restrainer do?
    prevents reducing agents from producing fog, which is created when unexposed silver bromide crystals develop
  82. what does a preservative do?
    slows oxidation of reducing agents by room air
  83. what is the solvent in the processor?
    water which is the medium in which chemicals are dissolved
  84. what does the fixer accomplish?
    clears and removes unexposed silver bromide crystals
  85. what does the transport system do?
    • moves film through processor
    • agitates chemistry
  86. what do deep racks do?
    • move film into and through solutions in developer, fixer, and wash tanks and between drying tubes in dryer section
    • has turnaround assembly at the bottom
  87. what does a crossover accomplish?
    moves film from the developer tank into the fixer tank and from the fixer tank to the wash tank
  88. when does replenishment of chemicals occur inside the processor?
    • for each film fed into the processor
    • activated by micro switch at end of entrance roller
  89. replenishment rates in a typical workday are based  on what size of film?
  90. what is the temperature maintained in inside the developer?
    90 to 95 degrees F
  91. what is the temperature in the dryer?
    120 degrees F
  92. Maintenance of processor: what is recommended daily?
    • wash crossover racks twice daily
    • drain wash tank
  93. Maintenance of processor: what is recommended weekly?
    clean deep racks
  94. Maintenance of processor: what is recommended monthly?
    • drain and clean by hand all tanks and dryer
    • put in fresh developer and fixer
    • add starter solution to developer chemicals
    • change developer filter
    • change water wilters
  95. When is sensitometric testing done for automatic processors?
  96. what does sensitometric testing check?
    • speed
    • contrast
    • base plus fog
  97. what does a densitometer measure?
    • speed step
    • contrast step
  98. what are pi line artifacts?
    • small marks 3.14 inches apart
    • caused by raised nick on roller scratching film
    • also by chemical stain or dirt
  99. increased developer temperature does what to a film? 
    • chemical fog
    • increased density
  100. what type of malfunction to the processor causes light films?
    developer too low
  101. what type of malfunction to the processor causes film to appear milky?
    poor fixer replenishment
  102. what type of malfunction to the processor causes dark flakes to appear?
    algae from wash water
  103. what type of malfunction to the processor causes dark films?
    • developer temp too high
    • developer overreplenishment
    • fixer contamination of developer
    • white light leak
    • crack in safelight
  104. what type of malfunction to the processor causes film fog?
    • developer contamination
    • developer overreplenishment
    • crack in safelight
    • developer temp too high
    • outdated film