dexa 3

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  1. Precision is expressed as what in bone densitometry?
    ability to reprodeuce the smae numerical result in the setting of no real biological change when the test is repeatedly performed in an identical fashion
  2. What is the purpose of figuring out the least signigicant change?
    to find the real biological change
  3. What are the "degrees of freedom" and how many do you need to have a statistically valid short term precision study with a 95% confidence level?
    the number of measurements that independtly contribute to precision value. Must have 30
  4. What are the 4 basic rules that are followed to choose a skeletal site to
    monitor the effects

    of diseases and drugs on the

    • 1) Measure the skeletal site or type of bone (cortical or trabecular) that is expected to be affected by the disease process or thearpy.
    • 2) of the site potentially affected measure the site at which the greatest change in BMD is expected.
    • 3)Use the site at which the BMD can be measured with the best precision
    • 4) Perpheral sites are not used for monitoring by any technique
  5. Why is trabecular bone the bone of choice to see changes in bone density? How
    much of

    the PA spine is trabecular and which
    regions of the femur are the most trabecular?

    because it has a higher metabolic rate than the cortical bone and more likely to see a change 3 or 4 vertebrae- total femur region then trochantric region
  6. What regions of the proximal femur make up the total femur area?
    femoral neck, Wards area, trochanteric area, and shaft
  7. Know that the larger and the more area you have, the higher the precision in

    changes and that is why the PA Spine
    is the preferred choice for monitoring changes in


  8. What are the Z’ prime values for 80% and 95% confidence levels?
    • 95% is 1.96
    • 80% is 1.28
  9. What is an in vivo study? What is an in vitro study?
    • A Vivo study when you use patients to do your cross calibration
    • Vitro study is when you use a phantom to do your cross calibration.
  10. What are some other examples of electromagnetic waves besides x-rays?

    Radio and Television waves, Microwaves, Radar, infared waves, visible and UV light, gamma radiation
  11. What is the definition of radiation and ionizing radiation?

    • Radiation- When energy is released and transmitted through a substance
    • Ionizing Radiation- Radiation that causes the release of an electron from its orbit around an atom when the radiation passes through the substance containing the atom
  12. What does rad and rem stand for?
    • Rad- Radiation Absorbed Dose used to express the quanity of radiation received by a patient
    • Rem- Rad Equivalent Man- quanity of radiation recieved by a patient, but the quality has been adjusted to reflect the type of radiation involved
  13. What are the SI equivalents of rad and rem?
    • Rad is Gy
    • Rem is Sv
  14. What is the quality factor or medical x-rays?
    1 rem=rads
  15. What is the Effective Dose Equivalent?
    a concept used to relate the magnitude of an exposure in Rems or Sv to the risk created by that exposure
  16. What is the tissue weighting factor of the whole body? Which body parts are the

    sensitive to radiation?

    • 1
    • Ovaries and Testes
  17. What is erythema? How many rads are needed to see this effect in 50% of the


    Reddening of the skin. 600 rads (6 gy)
  18. How many rads may cause permanent sterility in females and males?

    500 rads
  19. Which type of blood cells are the most sensitive to radiation?
    White Blood Cells - Lymphocyte
  20. What are the types of acute lethal radiation syndromes and what would be the
    most likely cause of death with each of these 3 syndromes?
    • Hemotologic Death- 10-60 days death occurs b/c of bacterial infection occurs w/in 2 weeks w/o medical intervention
    • Gastrointestinal Death- 4-10 days death occurs b/c of bacterial infrection affecting the crypt cells in the intestines
    • Central Nervous System Death- 72 hours-3 days Death occurs b/c of edema exerting pressure on the brain
  21. What are the names of the two types of biological effects seen with radiation

    and give examples of each?

    • Stochastic- cancer and mutations
    • Determininistic- acute radiation sickness and cataracts
  22. How does PA spine and proximal femur radiation doses compare to other forms of


  23. Do array or pencil beam scanners have a higher radiation dose?
    Array Scanners
  24. How far away from the x-ray source should you be as a technologist scanning a

    3 ft
  25. What are the ways to protect the public, the patient, and the technologist in


    No one undergoing the exam should be allowed in the room, place radiation warning signs on entrances
  26. What are the two types of radiation badges mentioned in this chapter and are
    they used for protection from radiation?
    • Film badges- changed monthly
    • TLD's- thermoluminscence dosimeter, more sensitive, can be worn up to 3 months
    • NO
  27. What is the maximum permissible dose to a fetus? What is the maximum
    permissible dose to a member of the public and to a
    radiation worker per year?
    • 500 mrem
    • 100mrem(0.1) per year
    • 5000mrem 5 rem a year
  28. Who is a “member of the public”?
    Anyone not undergoing radiologic procedures and who do not work w/radiation producing devices or substances
  29. What does ALARA stand for?
    • As
    • Low
    • As
    • Reasonably
    • Achievable
Card Set:
dexa 3
2011-07-07 02:03:23

mr answers
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