Principles

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Author:
cccdct123
ID:
52459
Filename:
Principles
Updated:
2010-12-11 22:38:33
Tags:
grid radiography kvp xray
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Description:
grid errors, density
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  1. Off focus error
    SID is wrong. Ok in the middle
  2. Lead content is high with what frequency and ratio?
    Lowfrequency but high ratio
  3. What is grid cutoff?
    Undesirable absorption of primary radiation
  4. Two types of moving grids
    Reciprocating and oscillating
  5. Intersection at top of grid radius?
    Convergence line
  6. Decrease in distance between strips results in
    Increased grid ratio
  7. Grid ratio is
    Height divided by interspace distance
  8. Order of tissue density?
    Air fat water muscle bone
  9. Densities of tissues?
    Air 1.29. Fat 916. Water 1000. Muscle 1040. Bone 1650.
  10. Decrease in atomic number causes
    Increase in scatter
  11. A 10 inch air gap is same as what grid?
    15:1
  12. Density is measured as
    Kg per meter cubed
  13. Automatic collimation is called
    PBL- positive beam limitation.
  14. Four Advantages of collimators
    Light field, central ray. Less penumbra. Infinite field sizes.
  15. T/F. Scatter helps create the image
    False, it causes fog
  16. When the beam restrictor is close to the tube, this is created
    Penumbra
  17. At 120 kvp, interactions are what percent PE absorption and what percent Compton?
    25 and 75
  18. Examples of beam restrictors include
    Cones. Cylinders aperture diaphragms and collimators
  19. Off focus radiation comes from
    Somewhere other than the focal spot, such as the tube
  20. Lead content of a grid is determined by
    G over cm 2
  21. Clavicle test
    • Center lock tube
    • Crosswise small IR
    • Right marker, in light field
    • Turn head to side
    • Central ray at mid clavicle
  22. Muscle atomic number
    7.64
  23. Water atomic number
    7.51
  24. Fat atomic number
    6.46
  25. Air atomic number
    7.78
  26. Atrophy osteoporosis, emphysema and acute osteomyelitis are (destructive or additive) conditions?
    Destructive
  27. For additive conditions, increase the
    Kvp
  28. For destructive conditions, decrease the
    MAs
  29. The three main things that happen with the primary photons are
    Transmission, pe absorption, and compton interaction
  30. Primary radiation that interacts with outer shell electrons and change direction is
    Compton interaction
  31. When kvp increases, scatter (increases or decreases) and contrast (increases or decreases)
    Increases, decreases
  32. Greater sharpness is from more or less OID?
    Less
  33. Grid conversion factor equals
    MAs with the grid divided by mAs without the grid.
  34. Grid conversion equation is:
    • Mas 1 over mas 2
    • equals gcf 1 over gcf 2
  35. Off level error happens when
    Tube is angled against grid strips
  36. if lead strips are 3mm high and interspace is .25 mm, what is the grid ratio?
    • 3.0
    • ------
    • 0.25. Equals 12:1
  37. A short sid has a ( more or less) divergent beam than a long sid
    More
  38. The incident photon knocks out an outer electron and changes direction with less
    Energy
  39. At 50 kvp, interactions are --- percent kvp and ---percent Compton
    50/50
  40. At 120 kvp, interactions are what percent PE and Compton?
    25/75
  41. Kg per m3 is the unit of
    Density
  42. Ion chambers ionize the air inside in proportion to what?
    In proportion to the radiation striking the chamber during the exposure.
  43. what happens to the ionized air in the ionization chamber after it is exposed to radiation?
    It completes an electrical circuit, the current is amplified, and termination of the exposure is signaled.
  44. What metal is used inside the ionization chambers of the AEC?
    Aluminum strips.
  45. AEC devices provide diagnostic quality exposure for structures positioned how?
    Directly over the ionization chambers.
  46. What are the most critical guidelines for using ionization chambers of AEC?
    Positioning the patient properly, and selecting the correct chambers
  47. What does a phototimer use to regulate exposure?
    A thyratron
  48. What is an older term for an AEC device?
    A phototimer

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