XR202 Exposure

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Author:
Shutrbug20
ID:
91145
Filename:
XR202 Exposure
Updated:
2011-06-21 23:30:41
Tags:
Contrast
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Description:
Chapter 9 LR Book
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  1. Contrast
    • Range of Gray shades
    • The difference in density between adjacent areas of image
    • Allows anatomic detail to be visualized
  2. Clear Detail
    Definition and Resolution
  3. Distortion / Magnification
    Size and Shape
  4. Visual Properties Catagories:
    Photographic Properties - Contrast
  5. Photographic Factors:
    Contrast
    • 3 Types:
    • Radiographic
    • Subject
    • Film
  6. kVp
    • Primary control Contrast
    • By penetrating power
  7. kVp
    Visualized (2)
    • Shades of Gray
    • Differences between organs / tissues
  8. Contrast
    Enhances
    Information
  9. Black
    • Less radiation absorbed by body
    • More radiation absorbed by film
  10. White
    • More radiation absorbed by body
    • Less radiation absorbed by film
  11. Long Scale Contrast
    More range of gray scale
  12. Short Scale Contrast
    More Black and White tones
  13. High Energy Radiation
    • Short wave
    • More penetration
    • Long Scale
    • More gray tones
  14. Subject Contrast
    • Depends on radiation attenuated as it enters,
    • Passes, and exits tissue of body
    • Known as Arial Image
  15. Film Contrast
    • Type film
    • Processing conditions
    • Use of screens / no screens
  16. Film Contrast
    Screens
    • Convert x-ray to light
    • = more contrast
  17. 15% Rule
    • Raise kVp 15%
    • Doubles kVp penetration
    • Visibility decreases contrast
  18. 15% Rule
    kVp vs mAs
    • Increase / decrease kVp 15%
    • Similar to increase / decrease mAs by 50%
  19. Distance
    kVp
    • Any change in distance
    • No contrast change
    • No penetration change
  20. Other Contrast Factors
    • Beam restriction
    • Beam filtration
    • Tissue compression
  21. Other Contrast Factors
    Beam Restriction
    • Reduces scatter from interacting with body
    • Prevents excessive scatter from fogging film
    • Reduces increased density and decreased contrast of image
  22. Other Contrast Factors
    Beam Filter
    • Filters added to radiation beam
    • Eliminate nonuseful, soft, low-energy (long-wave) rads
    • Hardens beam by only allowing high-energy (short-wave) rads to pass through
    • Contrast improved
  23. Other Contrast Factors
    Tissue Compression
    • Reduced tissue thickness
    • Contrast reduced from increased kVp penitration
  24. Visual Properties
    Geometric Factors
    Recorder detail of image and accuracy of true edges of anatomy to be seen
  25. Visual Properties
    Geometric Factors
    Detail
    • Degree of info
    • Definition of anatomy
    • Resolution / sharpness of lines that separate structures
  26. Visual Properties
    Geometric Factors
    Image Influence
    • Focal spot size (FFS)
    • Source to image distance (SID)
    • Object to film distance (OFD)
    • Screens used / not used
  27. Geometric Blur
    (Penumbra)
    Gradient unsharpness / edge of image
  28. Focal Spot
    Small is better
    • Single most important factor
    • Recording detail of anatomy
  29. Geometric Blur
    Greater SID
    • Reduces geo-blur
    • Improves detail
  30. Object to Image Distance (OID)
    Image Distortion
    • Place part as close to IR as possible
    • Magnification occurs as you separate from IR
    • Enlarged and fuzzy image
  31. Magnification
    • Size distortion
    • Decrease Object to image distance (OID) or
    • Increase Subject to image distance (SID)
  32. Magnification
    Formula
    SID / SOD = x Times magnification
  33. Intensifying Screens
    • Effects image detail according to size of phosphor crystals
    • Small = less bluring, less diffusion of light created by crystals
  34. Film Resolution
    • Ability of crystals within film emultion to efficiently record info
    • Crystal size
  35. Grids
    • Designed to absorb scattered radiation
    • Greater exposure needed above 12cm thick
    • No grid to grid = 4x more mAs needed
  36. Grid Ratio
    • Height of lead strips to distance between lead strips
    • 6:1 not as good as 10:1
  37. Filtration
    • Filter beam
    • Remove lower-energy rads
    • Aluminum = added filtration
    • .5mm in tube as glass and oil = inherent filtration
    • 2.5mm minimum filtration =
    • Added filtration + inherent filtration = Total filtration
  38. Processing
    • Safelights
    • Film Age
    • Chemicals
  39. Processing
    Safelights
    • Proper filter
    • Distance
    • Color
    • Size
  40. Processing
    Film Age
    No expiration date used
  41. Processing
    Chemicals
    • Time-temp process
    • Increased temperature = increased density
  42. Image Quality Factors
    • Density
    • Contrast
    • Resolution
    • Distortion
  43. Off-Center Grid
    • CR must be centered along center axis of grid / table
    • If not, Lateral de-centering will occur
  44. Off-Level Grid
    • Grid at angle from CR
    • Results in overall decrease density
  45. Off-Focus Grid
    • Must be used at a specific distance
    • Has focal range (usable distance)
    • Portable = smaller ratio for more error latatude
    • Bucky has larger ratio
  46. Upside-Down Grid
    • Placed label down instead of up
    • Will block all but straight CR in middle
  47. High kVp
    • Long Scale Contrast
    • More gray tones
  48. Low kVp
    • Short Scale Contrast
    • Less gray
    • More B&W
  49. Short Scale
    Use
    • Low kVp
    • On extremities
    • More B&W
  50. Long Scale
    Use
    • High kVp
    • On chest / abdomen
    • More gray scale tones
  51. Long Scale Contrast
    • Low Contrast
    • More gray tones
    • More detail
  52. Short Scale Contrast
    • High Contrast
    • Less gray tones, more B&W
    • Less detail
  53. Radiographic Density
    • Less absorbed radiation = lung = black
    • More absorbed radioation = bone = white
  54. Radiopaque
    • Higher atomic number
    • Absorbs more radiation
    • Bone
    • White
  55. Radiolucent
    • Lower atomic number
    • Absorbs less radiation
    • Tissue
    • Gray
  56. Subject Contrast
    (Patient)
    • Differential Absorption
    • Affected by:
    • Patient size
    • Type of tissue
    • Part be radiographed
  57. Greater Absorption
    • High contrast
    • Short scale
    • Low kVp
  58. Lesser Absorption
    • Low contrast
    • Long scale
    • High kVp
  59. Film Contrast
    Factors
    • Film
    • Proceing
    • Screen vs non-screen
  60. Replenisher Speed
    Too Low
    • Lower contrast
    • More gray tones
    • Radiographic fog
  61. Increase in kVp
    • Decrease in contrast
    • Long scale
    • Decrease in density
    • More grays
  62. Decrease in kVp
    • Increase in contrast
    • Short scale
    • Increase in density
    • More B&W
  63. Scatter Radiation
    • Increase with increased patient thickness
    • Increase with larger field sizes
    • Decreases in atomic number
    • Bone / muscle absorbs more radiation, less scatter
  64. Radiographic Fog
    • Graying of overall film
    • Weak appearance of overall detail and densities
  65. Primary Cause of Fog
    Secondary Radiation (Scatter)
  66. Collimation
    • Reduce primary radiation to patient
    • Limit fied size to area of clinical interest
    • Improved image quality, increase contrast, reduce fog
  67. Controlled Contrast Factors
    • Film
    • Developer
    • Grid
  68. Grids
    • Placed between patient and film
    • Used to reduce scatter radiation
    • Increase grid ratio = increase tech factors
    • Higher grid ratio = more critical centering
    • Focus grid ratio = specific SID range
  69. Bucky Grids
    Move to eliminate grid lines
  70. Grid Contrast
    • Use of a grid will increase contrast
    • Scatter is eliminated, less fog, more contrast (B&W)

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