RAD-171 CH.15 BEAM RESTRICTION

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Author:
anatomy12
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248475
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RAD-171 CH.15 BEAM RESTRICTION
Updated:
2013-11-22 11:33:08
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xray
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xray
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  1. what is the purpose of collimation
    improves the quality of your image and reduces scatter
  2. when does most scatter happen
    how can we reduce some scatter
    lower kvp and doubling your mas or collimating more
    bigger body parts and high kvp
  3. what are the three affects on the increase of kvp
    • increased transmission
    • decreased photoelectric absorption
    • increased compton scatter
  4. what happens to photoelectric absorption when you decrease kvp
    it increases
  5. what contributes more to patient dose
    a decrease in kvp which causes an increase in patient dose even more
  6. which exposure factors will produce higher contrast and more penetrating scatter
    • 30 mAs 75 kvp higher contrast b/c lower kvp
    • 15 mAs 85 kvp more penetration and scatter higher kvp
  7. increase field size increases volume of tissue _______ which results in what?
    • irradiated
    • increased scatter
  8. what happens when we decrease field size
    • decreases beam quantity decreases scatter
    • shortens scale of contrast in image
  9. ______and _______ produce more scatter
    thicker and denser
  10. what devices are used to improvoe spatial resolution and contrast
    compression devices
  11. what are the four affects of using compression devices
    • decreases patient thickness
    • results in lower patient dose brings tissue closer to film
    • utilized in mammography
  12. what are all the benefits of using beam restricting devices
    • scatter decreases
    • scale of contrast shortens
    • visibility of detail increases
    • unecessary tissue exposure decreases
  13. list the four beam restricting devices
    • aperture diaphragm
    • cone or cylinders
    • collimators
    • anciallary devices
  14. what is the most simple beam restricting device for collimation
    what is it made of
    • aperture diaphragm
    • it is a lead lined or lead plate attached to the xray tube
  15. in what situations do we use aperture diaphragms
    • dental equipment
    • trauma units
    • dedicated chest or head units
  16. which beam restricting devices is used with a fixed application with an IR and a fixed SID
    aperature diaphragm
  17. what are the disadvantages in using a aperture diaphragm
    • causes penumbra (lack of sharpenss of the film)
    • -due to the proximity of the port it decreases the beam restrictor is to the object being imaged
    • increased off focus radiation (due to distance from focal spot)
  18. aperature diaphragms can be supplmented with what two structures
    cones and cylinders
  19. which has more penumbra cone or a cylinder
    a cone because the divergence of the beam is greater in a cone than cylinder
  20. what is the forumal for determining field size
    image size = SID x diaphragm diameter/distance from focal spot to diaphragm
  21. cone aperture diaphragms are mostly used where
    in dental radiography
  22. cones and cylinders are used for what?
    greater detail in small areas (reduction in scatter makes the image sharper)
  23. what is the purpose of the first set of shutters in collimation
    and the second set of collimation shutters
    • to reduce off focus radiation
    • to restrict the beam (adjusted by the technologist length and width of light field)
  24. mirror in the collimator box is what?
    added filtration
  25. what do we use to test the beam coincidence of the light field
    8 penny test
  26. while doing the 8 penny test what is the accuracy limit range
    2% of a forty inch SID  = .8
  27. what is the benefit of the collimator housing
    it has an alignment light that helps to center beam with the IR
  28. what are ancillary devices
    • lead blockers -shields
    • lead masks - attached to collimator

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