RAD-171 X-Ray Tube Chapter 6

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anatomy12
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233904
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RAD-171 X-Ray Tube Chapter 6
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2013-09-11 19:48:08
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xray tube
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  1. Where do the x-rays come from
    from the anode rotating disk after it receives emitted electrons from the cathode side
  2. What is Kv
    kilovoltage is the strength or power of the electrons or photon beam
  3. what is ma
    ma is milliamperage which is the number of electrons or photons emitted across the anode and cathode space or produced
  4. the higher the kv the stronger the ____?
    x-ray
  5. What allows x-rays to be made under very special conditions including a source of electrons, an appropriate target material, a high voltage and a vacuum?
    the x-ray tube
  6. List the structures located on the cathode side of the x-ray tube?
    • focusing cup
    • filaments
    • filament wires (associated wires)
  7. List the structures located on the anode side?
    • anode rotating desk made of tungsten
    • focal spots on rotating desk
    • molybdenum neck shaft
    • rotor that houses the shaft
    • ball bearings located around the shaft inside the rotor housing
    • stator located externally of the x-ray tube
  8. What is the anode side of the xray tube?
    cathode side?
    • positive side
    • negative side
  9. Where is the area that the electrons hit after thermionic emission?
    focal point on the anode rotating disk
  10. What is the cathode and anode housed in?
    glass envelope
  11. what is the glass envelope housed in?
    a steel protective covering, it is the part that the radiographer actually moves and touches
  12. What part of the x-ray is always located outside of the x-ray tube
    the stator
  13. In what shape does the xray beam comes from after it hits a focal point
    divergence shape of photons that target the material
  14. Where is the source of electrons?
    on the cathode electrode of the xray tube
  15. What 3 parts consist of the cathode end?
    • focusing cup
    • filament tungsten wiring
    • associated wiring entering in for the electrons
  16. Where are the filaments located?
    in the focusing cup
  17. What element is the filament made out of in the focusing cup?
    tungsten
  18. Why is tungsten used? (2 reasons)
    • high melting point
    • it is difficult to vaporize
  19. What is melting point of tungsten?
    3370 degrees C
  20. What is the main function with filament size
    provides clarity of the x ray image
  21. what size is the best filament to use
    small filament
  22. When do we not use a small filament
    when not imaging bigger and thicker anatomy like the femur abdomen pelvis
  23. what happens when you increase mas?
    the higher the mas the more electrons get applied to filament, thus more electrons hit the focal point which results in more xray beams
  24. What is another word for Mas?
    current
  25. what is the space charge
    it is when electrons are liberated or hang around the surface of the filament (wires) and form an electric cloud called space charge
  26. what is thermonic emission?
    It is the process by which electrons are boiled off the filaments or when they bounce off enter the anode side
  27. At what temperature will the tungsten filament no exhibit significant thermonic emission?
    at 2200 degrees Celsius if it is below it will not be emitted it has to be hot enough
  28. What is the main function of the filament in general?
    to provide enough resistance to the flow of electrons so that heat is produced and cause thermionic emission (which is when the electrons bounce off the filament and hit a focal spot)
  29. What is the first step in an xray exposure?
    rotor switch
  30. What happens when the xray tube is turned on?
    a mild current is sent to the filament, which allows it to be preheated and ready for exposure at all times
  31. What can be done in prevention of degradation of the xray tube?
    pressing the rotor switch and the exposure buttn at the same time
  32. What is the approximate life of an xray tube and how much is needed to replace them if damaged?
    • 6-9 hrs
    • costs 10k to replace
  33. What happens if the rotor switch is activated prior to exposure?
    degradation of the tube happens earlier which can be prevented
  34. What divergence has better quality in regards to detail?
    the smaller divergence beam because the amt of photons that are emitted outside of the central ray come at a smaller angle than if it were to come down on a wider angle creating a blurry image on the outside of the area of interest
  35. Why is the middle ray or beam the beast out of all the photons?
    b/c it is the straightest
  36. What causes a bigger divergence beam?
    larger focal spot
  37. What is the focusing cup
    it is a shallow depression on the cathode side or assembly designated to house the filaments
  38. What element is the focusing cup made out of?
    nickel
  39. What is the purpose of the nickel made focusing cup?
    its purpose is to narrow the amount of thermionic emission to the anode
  40. What happens when two atoms are of the same charge ?
    So, what charge is the focusing point provided with?
    they repel one another and spread out or bloom

    low negative charge potential b/c of its shape it focuses electrons toward one another
  41. what is the biased focusing cup
    and what does it cause
    it is the cup that maintains at a more negative voltage than the filament

    causes the the electron stream to become narrower as it goes towards the anode
  42. where is biased focusing cup used often?
    in mammography
  43. what is called when it is possible to decrease size of the focal spot
    based focusing cup
  44. What is the space charge effect?
    happens when more and more electrons build up in the area of the filament and their negative charges begin to oppose the emission of additional electrons
  45. What is the phenomenon that limits the tubes maximum mA range from 1000-1200?
    space charge effect
  46. What is the maximum mA range of the space charge effect?
    1000-1200
  47. what is the other phenomenon that deals with the efficiency of the xray tube?
    saturation current
  48. When is the filament saturation achieved?
    when there are no further thermionic electrons
  49. What happpens to thermionic emission as the kVp increases?
    as kVp increases more electrons r a greater percentage of electrons are driven to the anode
  50. What is positively charged electrode?
    the anode
  51. What is the purpose of the anode assembly?
    serves to decelerate the electrons as well as store and dissipate (disperse)
  52. What area or part of the xray tube serves as target area for the high voltage electrons from the filament?
    anode side
  53. What is the target surface?
    it is where the surface where the electrons are suddenly stopped, resulting in the production of x ray photons
  54. what are the three main portions of the anode assembly?
    • anode roatating disk
    • rotor
    • stator
  55. What are the two types of anodes?
    rotating and stationary anodes
  56. What are all x-ray tubes in radiology departments? (certain type)
    rotating
  57. When does the rotating anode actually start turning and why?
    during exposure to make a much larger target area
  58. The faster the the anode rotates the _____ the ______ dissipation ability
    • better
    • heat
  59. What is the outer material of the focal track or the target area made out of?
    Inner?
    • tungsten
    • molybdenum 5-13 cm in diameter
  60. What is the rpm range of heat dissipation on the anode rotating disk?
    3400-10000 rpm
  61. what is the outer covering of the focal track composed of?
    rhenium alloyed tunsgten
  62. whats another purpose of anode assembly?
    it serves as a pathway for the high voltage flow during exposure
  63. what is the rotor attached to?
    the molybdenum shaft which is part of the anode rotating disk
  64. Why is tungsten the primary metal of choice? (3 reasons)
    • high melting point
    • heat conducting ability (difficult to vaporize)
    • high atomic number
  65. what is the main function of the glass envelope?
    The main function of the glass envelope surrounding the x-ray tube is to create a vacuum environment for more efficient x-ray production

    If Air/Gas present. ē's from electron stream interact with air/gas molecules. result in harder to control x-ray production
  66. How does tube failure happen?
    Loss of the tube's vacuum reduces x-ray production, produces more heat & leads to eventual tube failure
  67. The glass used in x-ray tubes must be...?
    • Pyrex or heat resistant variety
    • Heat is the main product of ē interactions at the target
  68. How does tube failure happen?
    Loss of the tube's vacuum reduces x-ray production, produces more heat & leads to eventual tube failure
  69. To keep the rotor bearings from burning out, what materials is placed between the disc and rotor
    molybdenum or graphite or a combination of such materials

    Molybdenum has a high melting point like tungsten but is a relatively poor conductor of heat (more of an insulator than tungsten)
  70. In a x-ray tube, vaporized tungsten can come from the _______ or _______.
    filament or anode target surface
  71. what is the purpose of collimation?
    to limit the amount of xray exposure towards the patient and that radiation only goes to area of clinical interest
  72. what part of the xray tube serves as a source of the electrons
    the cathode
  73. the _____ and _____ have a great effect on the ability of a particular xray tube to image fine details
    length and width
  74. what happens every time the rotor switch is pressed or depressed?
    it loses life in the filament
  75. what happens when high voltage is released at exposure
    the entire thermionic cloud is avalable to be driven toward the anode target where the xray photons will be produced
  76. What happens to the electrons as kVp increases?
    a greater percentage of thermionic electrons are driven towards the anode
  77. when is filament saturation achieved?
    when there is no further thermionic electrons to be driven towards the anode
  78. What will happen if you try to increase kVp at the level of filament saturation?
    • it will not increase the mA
    • the ray circuitry automatically adjusts this when factors are changed by the operator
  79. what motor turns the rotor?
    stator

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