XR202 Exposure

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Author:
Shutrbug20
ID:
90810
Filename:
XR202 Exposure
Updated:
2011-06-19 14:02:39
Tags:
Density
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Description:
Chapter 9 LR Book
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  1. Density
    Darkness
  2. Contrast
    Range of gray shades
  3. Clear Detail
    Definition and resolution
  4. Distortion / Magnification
    Size and shape
  5. Visual Properties
    Catagories (two groups)
    • Photographic Properties :
    • Density and Contrast
    • Geometric Properties :
    • Distortion and Magnification
  6. Photographic Factors
    Density
    • Overall blackness of total image
    • Controlled by mAs (quantity of radiation)
    • Directly proportional to amount of mA used and length of time (more rads = more blackness/density)
    • mA x S = mAs
  7. Primary Density Controlling Factors
    • mA
    • mAs
    • S
    • SID
  8. Photographic Factors
    Density (mA doubled)
    Quantity of rads doubled
  9. Photographic Factors
    Density (time doubled)
    Quantity of rads doubled
  10. Exposure Factors
    • mA
    • Time
    • kVp
    • SID (source to image distance)
  11. Exposure Factors
    (Other Effects)
    • Heel Effect
    • Tube Alignment
    • Film and Body Part
    • OFD (object to film distance)
    • Tissue Thickness
    • Screen Selection
    • Collimation and Beam Filters
    • Fog
    • Film Processing
  12. Reciprocity Law
    • Any combo of mA x T factors that are equivalent
    • mAs will produce same density
  13. mAs
    Primary control of Density
  14. mAs Selection Factors
    • Size of focal spot
    • Amount of time needed
  15. Focal Spots
    • Primary factor
    • Controlling recorder detail (geometric property)
  16. Focal Spot
    (Small)
    • Sharper detail
    • 300mA or less
  17. Focal Spot
    (Large)
    • Less Detail
    • Use if object greater than 12cm thick
    • 400mA or greater
  18. Heat Unit (HU)
    • Amount of heat tollerance
    • How much a tube can handle
    • mA x T x kVp
  19. Control Density
    Other Factors
    • kVp
    • SID
    • Heel Effect
    • Processing
    • Fog
  20. Control Density
    Other Factors
    kVp Increases
    • Increase penetration
    • Density increases (increase scatter)
    • Controlled by addition of Grid
  21. Visible Change
    Film
    Must have 25-30% difference
  22. Grid
    • Controls Density
    • By absorbing scatter rads
    • Greater exposure needed above 12cm thick object
    • No Grid to Grid = needs 4x more mAs exposure
  23. Grid Ratio
    • Hight of lead strips to distance between lead strips
    • Width stays constant
    • Hight will change to give different ratios
    • 6:1 is less efficient than 12:1
    • Higher the number the better
  24. Inverse Square Law
    • Intensity of radiation is inversely proportional to square of distance
    • I2 = I1 x D12 Divided by D22
  25. Heel Effect
    • Radiation intensity diminishes along a line parallel with long axis of tube
    • Intensity is stronger on Cathode side
    • Align thicker body part to Cathode side
  26. Film Fog
    • Generalized
    • Unwanted increase in density
    • Makes structures dificult to see
  27. Artifacts
    • Foreign marks
    • Unwanted marks
    • (physical or chemical or light)
  28. Intesifying Screens
    • Effects image detail according to size of Phosphor Crystals
    • Small crystals = less blurring of image because less diffusion of light created by small crystals
  29. Film Resolution
    Ability of crystals within film emultion to efficiently record information (Silver Halide)
  30. Filtration
    • Filter beam
    • Remove lower-energy rads
    • Aluminum = called added filtration
    • .5mm in tube as glass and oil (inherent filtration)
    • Total = 2.5mm minimum filtration (inherent + added)
  31. Processing
    • Safelight = proper color filter, distance, size
    • Film Age = not used past expiration date
    • Chemicals = time-temp process; increase temp = increase density
  32. OFD
    Object to film distance
  33. SID
    TFD
    FFD
    • Refer to Tube
    • Source to Image Distance
    • Target to Film Distance
    • Focal Spot to Film Distance
  34. SID
    Change
    Density Stays Same
    • Increase SID = mAs times 4
    • Decrease SID = mAs times .25
  35. Compton Effect
    P.E.
    • Scatter effect = fog =
    • Overall grayness / darkness
    • Density goes up
  36. SID vs Density
    • SID decreases = Density increases
    • SID increases = Density decreases
  37. 15% Rule
    • Every 15% increase in kVp
    • Must reduce mAs by 50% (cut mAs in half)
    • Every 15% decrease in kVp
    • Must increase mAs by 50% (double mAs)
  38. Slight Overexposure Correction
    Reduce kVp by 7%
  39. Overexposure Correction
    Reduce kVp by 15%
  40. Slight Underexposure Correction
    Increase kVp by 7%
  41. Underexposure Correction
    Increase kVp by 15%
  42. Silver Halide
    Used as light sensitive component of x-ray film
  43. Latent Image Caused By
    • Light
    • X-rays
  44. Cassette Advantage
    • Because of intensifying screens:
    • Lower mA needed
    • Faster exposure times
  45. Phosphors
    • Fluoresce (give off light)
    • When hit by x-rays
  46. Film Screen
    Speed
    • Slow (detail)
    • Medium (par)
    • High (fast)
  47. Rad Protection
    Most Important
    Use High Speed film screen
  48. Film Storage
    • Upright to avoid static from weight
    • Closest due dates up front
  49. Safe Light
    Distance
    • Minimum distance 3 feet
    • From work bench
  50. Safelight Fog
    • Film more sensitive after exposure
    • During developement
  51. Static Marks
    Caused by dry air
  52. White on Film
    Fixer before developer
  53. Crescent Marks
    Bends in film (finger nails)
  54. Reticulation
    • Web like markings
    • Extreme difference in solutions
  55. Fog
    • Light leak
    • Scatter x-rays
    • Chemical Vapor
  56. Dirty Film
    • Dust
    • Poor storage
  57. Radiographic Density
    Recorded Detail
  58. Distance and Radiation Intensity
    Relationship
    The intensity of radiation is inversely proportional to the square of the distance
  59. Change Focal Spot
    • Without changing mAs
    • Changes resolution / detail
  60. Screen Types
    • Calcium Tungstate
    • Rare-Earth (more sensitive to light) Desireable
  61. Sodium Sulfate
    • In both developer and fixer
    • Used to prevent oxidation
  62. Auto Developer
    Time Control
    • Time kept by roller system
    • Maintains proper time in each stage of process

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