Physics and Quality and Safety Review

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Physics and Quality and Safety Review
2015-06-14 22:34:55
physics radiology

Radiology Physics and Quality and Safety review
Show Answers:

  1. What is the appropriate thickness of a lead apron?
    0.5 mm
  2. What is the minimum ANNUAL radiation dose allowed for radiation workers?
    50 mSv
  3. What is the minimum ANNUAL radiation dose allowed for PREGNANT radiation workers?
    5 mSv (1/10 of annual dose of non-pregnant radiation worker)
  4. What is the minimum radiation dose required in order to get early transient erythema?
    2 Gy
  5. What is the maximum EYE dose equivalent for a RADIATION worker?
    150 mSv
  6. What is the maximum dose of radiation acceptable for 1 hour in a nuclear medicine waiting room?
    2 mrem (0.02 mSv)
  7. What is the definition of a major radiation spill?
    100 mCi of Tc or Thallium (lower energy)

    10 mCi of Gallium or Indium (medium energy)

    1 mCi of I-131 (high energy)
  8. What is the maximum possible fetal dose?
    0.5 mSv every month

    5 mSv for the duration of the pregnancy
  9. For a radiation worker, what is the maximum annual dose permissible for skin/individual organs?
    500 mSv
  10. For the public, what are annual limits for radiation exposure?
    5 mSv - Effective dose limit

    15 mSv - Lens of eye

    50 mSv - Skin/hands/feet/organs
  11. What is side lobe artifact?

    Side lobes are multiple beams of low-amplitude ultrasound energy that project radially from radial expansion of piezoelectric crystals

    - Seen primarily in linear-array transducers

    - Strong reflectors present in the path of these low-energy, off-axis beams may create echoes detectable by the transducer.

    - Most likely to be recognized as extraneous echoes present within an expected anechoic structure such as the bladder.
  12. When incoming electrons interact with the target at the anode, where is radiation intensity higher?
    Cathode side - x rays have less material to go through

  13. What is the definition and units of absorbed dose?
    Absorbed dose is the concentration of energy deposited in tissue as a result of an exposure to ionizing radiation (measured in mGy)
  14. What is the difference between equivalent dose and absorbed dose?
    Equivalent dose is an amount that takes the damaging properties of different types of radiation into account (unit Sv (Joules/kilogram))

    Absorbed dose tells us the energy deposit in a small volume of tissue. Equivalent dose addresses the impact that the type of radiation has on that tissue. Also known as the " biological dose," the dose equivalent is calculated as the product of absorbed dose in tissue multiplied by a quality factor and then sometimes multiplied by other necessary modifying factors at the location of interest.
  15. What is effective dose?
    Effective dose is a calculated value (measured in mSv) that takes three factors into account:the absorbed dose to all organs of the body,the relative harm level of the radiation, andthe sensitivities of each organ to radiation. The sum of the products of the dose equivalent to the organ or tissue (HT) and the weighting factors (WT) applicable to each of the body organs or tissues that are irradiated (HE = ΣWTHT).
  16. What are the common and standard units for equivalent dose?
    SI unit - Sievert (Sv)

    Non SI unit - rem

    1 Sv = 100 rem
  17. What is the relationship between cancer incidence and absorbed dose?
    Approximately 10% per gray (0.1% per rad)
  18. What is the threshold for cataracts from acute radiation exposure?
    0.5 Gy
  19. What is the most sensitive part of the cell cycle?
    M phase - mitotic phase
  20. What is the threshold for temporary epilation (hair loss)
    2 Gy
  21. What is the threshold for temporary sterility in males?
    0.1 Gy
  22. What is the unit of exposure?
    Quantity of charge in air due to ionization from x-rays or gamma rays (C/kg, historical unit was the Roentgen)
  23. What determines the absorption edge of a contrast agent?
    Binding energy of the k-shell electron
  24. What is the MQSA standard for maximum exposure of a CC view of a phantom mammogram?
    3 mGy
  25. What happens in Compton Scattering?
    • It occurs due to the interaction of the X-ray or gamma photon with the outermost (and hence loosely bound) valence electron at the atomic level. The resultant incident photon gets scattered (changes direction) as well as ejects the electron (recoil electron), which further ionizes other atoms.
  26. What is linear energy transfer?
    Average energy deposited in mass per unit path length
  27. At what threshold can acute radiation syndrome symptoms occur?
    1 Gy - may start seeing nausea/anorexia
  28. What is the threshold dose for permanent hair loss?
    7 Gy
  29. What is the maximum dose an individual member of the public may receive from the release of patients injected with radioactive material?
    500 mrem (5 mSv)
  30. What fluoroscopy dose is considered to be a sentinel event?
    15 Gy
  31. What is the threshold for PERMANENT sterility in males?
    6 Gy

    (3 Gy for females)
  32. What does NRC regulatory commission 10 CFR Part 19 deal with?
    Notices, instructions and reports to workers
  33. What is the definition of stochastic effects of radiation?
    As the dose increases, the probability of occurence increases (not severity)
  34. When should occupational doses be measured in an individual?
    Greater than 10% annual dose limit expected 

    > 500 mrem (5 mSv)/year
  35. What are the effects of rapidly switching magnetic field gradients?
    Can cause peripheral nerve stimulation - tingling/twitching sensation
  36. What factors are related to imaging time of a single MR slice?
    TR x number of phase encoding steps x average number of excitations
  37. What is the difference in recommended management comparing above the knee pulselessness versus distal below the knee pulselessness?
    Above the knee - surgical

    Below the knee - thrombolytics
  38. What are complications of static magnetic fields in MR scanners?
    Can cause augmentation of T waves