RAD-172 CH.26 RADI-DENSITY/IR EXPOSURE

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anatomy12
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262885
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RAD-172 CH.26 RADI-DENSITY/IR EXPOSURE
Updated:
2014-02-22 16:41:14
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xray
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xray
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  1. when we speak density that refers to film or CR
    when we speak IR exposure is that for film or CR
    • density relates to film
    • IR exposure deals with CR and DR
  2. density is defined as the overall ______ (2 reasons)
    • degree of blackness from the metallic silver deposited in the film emulsion
    • and the amount of radiation that has exposed the IR
  3. In the digital environment (DR) DENSITY can be expressed as ______
    image receptor exposure
  4. How is a CR/DR similar to an intensifying screen on a film
    what is the difference
    • they both absorb xray photons and then produce light
    • the difference is that there is a delay between the xray exposure and the production of the light
  5. how does CR work (general steps)
    • Take an xray on a cassette with only stimualible phosphor screen and now becomes an invisible latent image
    • next the cassette is run though a processing unit
    • it is scanned by a very small laser beam
    • when the beams strikes a spot it causes light to be produced
    • the result is the light that is produced is proportional to the xray exposure specific spot
  6. Are brightness and desnity interchangeable
    no
  7. what is brightness
    a monitor control function that can change the lgihtness and darkness of an image on a display monitor but it is not related to IR exposure
  8. what is window level
    • describes the digital post processing that produces changes in brightness so it is also appropriate to use when controlling the display of an image
    • deals with darkness of the image
  9. what is window width
    contrast
  10. does mas effect recorded detail
    no
  11. what is one of the photographic properties that comprise visibility of detail
    density
  12. what two properties allow us to view an image as visible
    because of density and contrast
  13. when dealing with film what is the best decision to make when justifying between excess and insufficient density
    always choice the factors produce the darker image
  14. if the density of your film is way to dark what must you adjust
    cut mas in half to much mas was used
  15. what causes quantum mottle
    low mas and high kv
  16. what are controlling factors
    factors that affect radiographic density and IR exposure
  17. what is the controlling factor of radiographic density(film)
    mAs (millapere-seconds)
  18. what happens to xray exposure as you increase mAs
    xray exposure increases proportionally and radiographic density increases as well
  19. Reciprocity law states what about film density
    if density is unchanged on film as long as mas stays the same
  20. if i took a knee xray at 60 kv @ 3.2 mas (80 ma .04s) what other ma stations could I use to get the same image
    • 160 ma and .02s
    • or 60 kv @ 3.4 mAs
  21. what percentage change in mas is necessary to cause a visible shift in density when using film and DR
    25-35 percent of mas
  22. what is the general rule of the thumb when changing mas
    cutting mas in half or doubling it
  23. when using DR what must we check to make sure we are exposing our patient properly
    the s value number b/c DR systems like when you over expose the image the computer will rescale the image and make it appear acceptable to the human eye
  24. what is the main influencing factor of radiographic density
    kVp
  25. what three things does kvp alter or change
    contrast, the intensity(strength) of the beam and some scatter is produced
  26. if your image is underexposed or too light what could you do to fix it
    you could increase kvp or double the mas
  27. what could you do to your image if it was exposed too much
    decrease kvp
  28. how does quantum mottle occur in CR and DR
    underpenetration or underexposed
  29. a visible change in density is usually detected with what percent change at low kv (30-50kv), 50-90kv 90-120kv
    • 4-5percent
    • 8-9%
    • 10-12%
  30. what is the 15% rule to compensate and maintain density
    • a 15% increase in kv causes a doubling of exposure to film
    • a 15% decrease in kv causes a halving of exposure to film
  31. why do we need to use the 15% rule
    to get a different scale of contrast (kv)
  32. a increase in kvp will _______ contrast and an a decrease in kv will _______ contrast
    • decrease
    • increase
  33. if you were using a single phase 2 pulse configuration would you need double the radiation or half of the radiation
    double because the single phase is less efficient and needs more energy photons to create the same image
  34. the closer the OID the _____ the IR exposure
    the further the OID the _____ the IR exposure
    • more
    • less
  35. when we decide to use large mA stations what happens to the focal spot
    Does FSS deal with density
    • focal spot increases because the electrons are not easily contained (focused) in the focusing cup
    • No it deals with detail
  36. when is the anode heel effect most noticeable
    • at short SID and Large IR size
    • (ex humerus on a wall bucky)
  37. how do we take advantage of the anode heel effect
    the thicker body part should be placed under the cathode end of the tube
  38. whats SID aka
    FFD focal film distance
  39. can SID alter the intensity of the beam
    yes
  40. the density maintenance formula is based on what?
    direct square law
  41. if you double your SID from 40 to 80 using 10 mAs what is you new mas to maintain density
    is patient dose increase or decreased
    • 40 mAs
    • the distance is doubled so you increase Mas 4x
    • patient dose decreases
  42. if you decrease the SID from 72 to 36 at 10 mAs what is your new mAs to maintain density
    • 2.5mas
    • since the distance is cut in half you decrease mas by 4x
  43. what would do to your mas once you increase your SID from 40-56-72
    decreasing SID
    • double mAs from 40in SID to 56in and then double again if you are going up to 72inches
    • halve mAs
  44. what is OID and does it affect IR exposure
    object to image distance and yes
  45. an increase in OID can _______ radiographic density and why?
    decrease b/c the air gap between the object and IR is more so less photons will hit the IR reducing density
  46. when using and SID ____ _____ radiation gets to the film and therefore causes a density difference when radiographing large patients
    less scatter
  47. can filtration(added coherent total compensating) affect radiographic density
    yes b/c when you use a filter it gets rid of xray photons unwanted photons low energy there reducing IR exposure
  48. what does beam restriction do (2 things)
    • reduces the total numbers of photons available and reduces the amount of tissue irradiated.
    • this reduces the amount of scatter produced and reduces overall density of the image
  49. when restricting the beam to a 4x4 with no grid what is required to maintain image density
    mAs compensation (double it) because collimating will underexpose the image
  50. As tissue thickness increases what also increases and decreases
    tissue density increases and radiographic density decreases b/c due to the thickness of the tissue less photons will hit the IR thus reducing IR exposure/density
  51. what does radiolucent contrast due to density and why?
    increase density because xray beams will penetrate right through since the contrast is radiolucent
  52. what does radiopaque contrast do to density and why?
    this contrast will decrease radiographic density because the contrast is absorbing the majority of the photons so less are hitting the IR reducing density
  53. does additive pathology increase or decrease tissue density
    does destructive pathology increase or decrease tissue density
    • decrease
    • increase
  54. what happens to body part thickness once the tube is angled
    if the angle is more than 15 degrees the tissue thickness increases therefor reduces density /IR exposure
  55. what is used to calculate necessary changes in Mas when using grids
    • maintaining density formula with grid conversion factors
    • (must use 4x more mas)
  56. what is the function of grids
    do grids add density to the film
    • it improves contrast by absorbing scatter
    • yes and the more efficient the grid the less radiographic density
  57. in film processing what three variables will increase density
    developer solution temperature increases, immersion time increases or replenishment rates increase, concentration
  58. what condition of the tissue require an increase of kvp
    additive conditions because it makes the body part thicker denser which requires more penetration
  59. what are some diseases that cause attenuation or additive conditions
    • pagets disease ostepetrosis acromegaly
    • hydro thorax
    • some cancers
    • empyema
  60. what are decreased attenuation (destructive) conditions
    • pneumothorax
    • osteomalacia and osteoporosis in bone
    • bowel obstructions in abdomen

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