RAD-171 X-Ray tube Chapter 6 Cont..

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anatomy12
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235201
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RAD-171 X-Ray tube Chapter 6 Cont..
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2013-10-20 16:12:23
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xray tube
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xray
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  1. what technical factor pushes electrons across the from cathode side to the tungsten anode rotating disk
    kVp
  2. What is the focal point
    a specific area or spot located on the rotating anode disk
  3. What will happen eventually to the anode rotating disk or to a specific area on the focal track
    the focal track material will begin to vaporize which causes the area to roughen or pit
  4. what does pitting do to the rotating anode disk
    it reduces the efficiency of the tube
  5. what process or change in focal track allows one to describe how old the focal track's tube is
    from the pitting that has occurred from years of wear and tear
  6. What happens to tungsten overtime
    what happens inside the xray tube because of excessive use of the disk
    • it begins to vaporize
    • it becomes gassy and produces less efficient x ray photons
  7. what exactly causes wear and tear of the focal track
    high usage of mAs or electrons
  8. if you are using an old machine in order to do a chest xray, what technical factor must be changed?
    you have to double the mAs because since the machine is old you need more electrons to make out the image which produces more radiation than if it was a new machine
  9. what causes a melting spot on the focal track (2 reason)
    when rotor fails to rotate the anode and also due to heat damage
  10. What is it called when you need to preheat the xray tube prior to taking any exposures?
    anode warm up procedure
  11. What is the average kVp and mA of a normal warmup procedure
    How many exposures are required for the warmup phase
    • 70-80 kVp
    • 100 or 200 mA
    • 3 exposures each 1 second a part
  12. what happens if you do not warm up the xray tube
    you can cause the anode disk to crack because of sudden pile up of heat
  13. what is the focal track
    is the circular path on the anode that will be impacted by the electron stream
  14. what are the alternative names for the target area
    focal spot focal point or focal track
  15. Is the focal spot the same as the filament
    • yes small filament small focal spot
    • large filament large focal spot
  16. which is a bigger filament .6 FSS or 1.2 FSS
    1.2 FSS
  17. what is the actual focal spot
    the physical area of the focal track that is impacted
  18. what is the effective focal spot
    the area of the focal spot that is projected out of the tube and down to the object being radio graphed
  19. which focal spot happens first the actual or the effective?
    actual
  20. what is the average angle range of the anode rotating disk
    7-17 degrees
  21. What main phrase is the THE LINE FOCUSING PRINCIPLE based on
    what does this do to the image ?
    "when the angle of the anode is less than 45 degrees the effective focal spot size will always be smaller than the actual focal spot size (physical area)"

    provide even more clarity of the image
  22. What causes the line focus principle to happen
    the design or the geometry of the anode target area is angled
  23. what is the purpose of the line focus principle
    to reduce the effective focal spot and will allows for the best resolution of detail
  24. what determines the sized of the effective focal spot?
    the actual focal spot
  25. what controls the size of the actual focal spot?
    the length of the filament
  26. what happens when the actual focal spot size increases?
    the effective focal spot increases as well but still remains smaller than the actual FSS
  27. what is the most common target angle on a rotating disk
    12 degress
  28. Can a 12 degree anode target area cover a 14x17 cassette at a 40'' SID
    yes
  29. what is the largest cassette size
    14x17 mostly used for abdomens
  30. if we increase mAs too much using a small filament what will happen?
    what do we use instead
    • although the machine wont let this happen, the small filament will not be able handle the massive amts of electrons
    • so instead we would use a larger filament
  31. Can small focal spot sizes utilize high mA stations
    no
  32. what is the anode heel effect?
    because of the geometry of the angle target area the radiation is intensifies on the cathode side
  33. why does the anode heel effect happen?
    • this happens b/c once the kVp pushes all the electrons over to the anode side the photons are more likely to be absorbed by the target material (located at the back of anode disk )
    • thus less photons are on the anode side and they are now exiting towards the cathode side
  34. B/c of the anode heel effect how much more photons can wind up being on the cathode side and anode side?
    20% more on cathode side 25% less on anode side
  35. What is the SID?
    source to image distance
  36. when is the anode heel effect more noticeable?
    when large film sizes are used at a short distance (refer to note book if you dont remember)
  37. In regards to the anode heel effect, why do radiographic tables have a head end?
    so the least amount of photons being emitted towards the head which means less radiation exposure
  38. How would you use the anode heel effect to your advantage
    when imaging thicker denser body parts, position the patient so that the cathode is over the bigger body parts thus it will recieve more radiation to make a better picture exposure is not a extreme factor b/c the body part is bigger you need more radiation
  39. what major is composed of the stator
    induction motor magnets that turn the anode
  40. what are the two switches to be depressed when taking an image
    • rotor/prep switch
    • exposure button
  41. what is the only part of the x-ray tube located outside the glass envelope?
    how is it able to function outside the tube?
    • the stator
    • the electromagnetic effects that cause the rotor to turn can function through the glass
  42. what happens when the rotor switch is pressed?
    it sends a current to the stator which then causes the rotor to turn the anode
  43. what happens if the stator is not functioning?
    the anode will not rotate resulting in the immediate melting of a spot on the target
  44. where is the rotor located
    inside the stator and inside the glass envelope
  45. what is the rotor composed of
    made of hollow copper cylinder and is attached to the anode disk by a molybdenum shaft
  46. what is the purpose of the ball bearings
    used as lubricants between the cylinder (or cuff) and the anode shaft to facilitate the turning of the anode disk
  47. what do you hear when the rotor switch is depressed
    ball bearings turning at high speed
  48. what does the stator do at the end of an exposure
    it runs in reverse to slow down the velocity (speed) of the rotor
  49. What parts are comprised of the the entire glass envelope
    • the anode and cathode assembly
    • but the stator is located outside the tube and glass envelope
  50. what is the glass envelope made out of?
    why is it sealed tight?
    different types of heat resistant Pyrex glass

    to maintain a high vacuum
  51. how thick is the window segment of the glass envelope where the primary beam exits
    much thinner
  52. what is the function of the glass envelope
    maintain the vacuum between the cathode and anode side
  53. what happens when you remove most of the air in the vacuum (hence its function)
    and does what to the xrays
    it allows the electrons flow from - end to + end without encountering gas/air atoms which increases the efficiency of the tube operation
  54. what is the protective housing the xray tube is made out of
    steel
  55. what does the steel housing control? (2 things)
    leakage radiation and scatter radiation
  56. how does the protective housing provide a means to control the tube?
    by isolating high voltages
  57. what is lined on the inside of the steel housing
    lead
  58. what substance is found between the housing and lead lining
    dielectric oil
  59. what is the purpose of the dilectric oil
    insulates the high voltage components of the tube housing aand absorbs much of the heat
  60. What is the specific term on how x-rays are produced at the anode
    isotropically (in all directions)
  61. where are unwanted photon beams absorbed?
    what is the primary beam?
    by the housing

    the primary beam consists of photons emitted through the glass window and housing window
  62. what is leakage radiation
    any photons that escape from the housing except at the window
  63. leakage radiation must no exceed what length
    100mR/hr at 1 meter
  64. what is mR
    milliroentgen
  65. what is another role of the protective housing
    protection of roughhousing by the radiographer
  66. is a patient or xray tech allowed to touch the housing during exposure
    no
  67. the dielectric oil is found between what two structures
    the glass envelope and the protective housing
  68. what is off focus radiation
    consists of photons that were not produced at the focal spot
  69. when does off focus radiation happen
    when high voltage electrons striking the target area produce scattered electrons or photons
  70. can off focus radiation strike other areas of the tube that can produce xray photons as well
    yes
  71. what absorbs most of the off focus radiation
    the housing
  72. what is the outcome of off focus radiation what do they do to the image
    What is the difference between scatter radiation
    • these photons create a "ghosting effect"
    • scatter radiation does not produce images like the off focus radiation
  73. what percentage of the primary beam is contributed to the off focus radiation
    25-30%
  74. how powerful are the off focus radiation photon beams
    not power low energy than primary beam
  75. what is the purpose of cooling curves and tube rating charts?
    used as safety measure to avoid thermal damage to the tube
  76. Any combination of technical factors on or under the curve is to be considered what?
    safe
  77. what are the three types of charts and cooling curves
    • tube rating charts
    • anode rotating disk
    • housing cooling curves

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