RAD-172 FINAL EXAM 23 31 34-36 37 39 40

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RAD-172 FINAL EXAM 23 31 34-36 37 39 40
2014-05-03 14:03:10

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  1. what is lines per millimeter
    measurement of recorded detail sharpness and resolution; the minimum size and space between objects that can be visualized on the final image
  2. line spread function
    the ability for a film/screen system to accurately measure the boundaries of an image
  3. modulation transfer function
    measures the resolving ability of a film/screen combination
  4. define size and shape distortion
    size distortion is magnification
  5. a decrease in SID would result in
    A decrease in OID would result in
    • an increase in size distortion
    • a decrease in shape distortion
  6. an increase in tube angle from 10-40 deg would result
    an in crease in shape distortion
  7. a misaligned CR would result in
    an increase in kvp would result in
    a change in OID from 2 in to 6 in would result in
    • an increase in shape distortion
    • no change on distortion
    • increase in size distortion
  8. a change in grid ratio from a 12:1 to 6:1 would result in
    a change in focal spot size would result in
    a change in mAs from 60-70 would result in
    • no change in distortion
    • no change
    • no change for distortion
  9. A change in SID from 72-40 would result in
    placing a part so that it is oblique to the IR or CR would ___
    an angle of the image receptor would result in ___
    • increase in size distortion
    • increase in shape distortion
    • in crease in shape distortion
  10. what is the magnification formula
    how do you find SOD if not given
    • SID over SOD
    • SID -OID = SOD
  11. which of the following would cause the most shape distortion
    10 angle
    45 angle
  12. which factor does not affect distortion
  13. the relationship between OID and size distortion is
    directly proportional
  14. what is the best SID and OID for least size distortion
    short OID and long SID
  15. Distortion is caused by ____
    from tube angle and position of the patient
  16. Distortion is the misrepresentation of the _____ or ___ of the structures being examined
        • size or shape
  17. size distortion is also known as
  18. what is one way to reduce size distortion
    getting rid of OID
  19. how do we control size distortion (magnification) as a tech
    positioning the body part accurately and fixing tube to maximize SID and minimize OID
  20. what is the object size formula
        • IS(image size)/MF (magnification Factor)
  21. shape distortion deals with what two things
    foreshortening and elongation
  22. when does foreshortening occur
    when the object is at an angle (rotated) and the CR is perpendicular to the film the image will appear shorter (squashed together) when compared to the object
  23. what is elongation
    type of distortion that occurs when object is parallel to the film the central ray is angled
  24. what is the standard sid used for an ap chest portable (3)
        • 40 SID

        • 56 SID

        • 72 SID
  25. what is the best grid to use when doing an ap chest portable
    using an lower ratio grid (6:1 8:1) with high frequency (178-200 lpi)

    this grid permits wide exposure and centering latitude
  26. how do we see distinct air fluid levels on an ap chest
    position patient semi erect or erect and the tube must be parallel to the floor in order to see distinct air fluid levels
  27. AEC controls what
    the length of the exposure (time)
  28. List the two types of exposures systems and explain them
    variable kvp system (kvp is changed and manipulated) and fixed kvp systems (kvp does not change mas is changeable)
    variable kvp system (kvp is changed and manipulated) and fixed kvp systems (kvp does not change mas is changeable)
  29. explain why the art of aec is the art of positioning
    because in order for aec to work effectively the body part must be positioned over that certain cell if it is not your image will under or over exposed
  30. what is the usual range of the radiographic densities
    .25 and 2.5 above base + fog
  31. what would happen if AEC was used on a large patient
    it would take a long time for enough exit radiation to get through the patient and into the photocell to charge the xray timer to the predetermined amt of charge exposure length would be long
  32. what would happen if the center cell was chosen for a pa chest instead of a two cell arrangement
    the image will be over exposed because the body part centered over the cent4er cell will be exposed appropriately (the thoracic vertebrae) and the lung field will be way too black because the outer cell was not selec
  33. what happens to your image  a pa chest was centered to low or too high
      • if it was too low the photocell will average the radiation for the abdomen and the chest will be overexposed
      • if it was too high the photocell will average the radiation and thickness for the upper chest (which is thinner) and the lungs will be underexposed
  34. what is minimum response time
    modern scr's may have a minimum reaction tim of less than _____ second
        • shortest amt of time it takes ionization chambers or photocells and tube to turn off  exposure

        • .001 seconds
  35. what is the backup time
    what is it used as
          • when aec is used the ordinary timer used for an exposure made without aec is the back up

          • it is use a safety device for the equipment to save the xray tube life
  36. according to us public law 90-602 generators must terminate the exposure at ______ for exposures above ____ kvp and ______ mAs for exposures under ____kvp
        • 600 mAs; 50

        • 2000 mAs;50 kvp
  37. can backup timers exceed tube limit and what is there percentage of the anticiapated manual exposure mAs
    • no
    • 150%
  38. what is a phototimer
    the old method consisting of a fluorescent screen that emitted light when struck by x-rays. These light photons were then counted by a photomultiplier tube (PM tube) and the exposure was terminated at a predetermined level. Chambers are beneath the bucky.
  39. high or increase in ma causes a _____ exposure time
    a lower or decrease in ma causes a _____ exposure time to produce adequate density which is best to pick
    • decrease (faster) shorter
    • increase (slower) longer time
    • high ma = short exposure time to beat pt motion
  40. what is aec and what does it use
    • automatic exposure control stops the exposure at the right time so that a radiograph with good density is produced using photocells
  41. when using aec, if the centering point for a c spine is at c7 instead of c4, how would the radiographic density be affected
    it will be overexposed
  42. if the back up time  is set at 0.5 second, what will happen tothe radiograph if the required exposure time is 0.8
    the image will be underexposed because not enough radiation will make it to meet 0.8 it will cut off at 0.5 which is not enough radiation needed to make the image
  43. an ionization device is located between what
    tabletop and the image receptor
  44. if the minimum reaction time is 0.01 second, what will happen to the radiograph if the required exposure is 0.008
    the image will be overexposed because 0.008 is shorter than 0.01 thus the exposure will not stop until it passes 0.008 and reaches 0.01 which is a longer time so more radiation will occur
  45. which of the following changes decrease the length of exposure when using AEC
    decrease mA
    decrease kVp
    change density -1
    change density setting +1
  46. change density setting -1 because it gives you 25 percent less radiation less radiation less length of exposure
  47. when should collimation be avoided
    too close collimation would result in
    not enough collimation would result in
    • when the collimation is close to the activated chambers
    • overexposed image
    • in a light image underexposed
  48. if low ma is selected the automatic exposure control will _____ to the time
    increase or longer
  49. if the primary beam is collimated from an activated field the field will ______
    operate as if the tissue was extremely dense
  50. what is the best way to control motion
    high ma short exposure time
  51. the _____ absorbs light and emits electrons:
    electrostatic lenses
    input phsophor screen
    output phosphor screen
  52. the ____ serves to absorb electrons and emit light
    output phosphor screen
  53. the _____ absorbs xray photons and emits light
    input phosphor screen
  54. the ______ are used to accelerate and focus the electrons in the image intensifier
    electrostatic lenses
  55. the input phosphor screen is composed of a layer of _____
    zinc cadmium sulfide
    cesium iodide
    cesium and antimony compunds
    calcium tungstate
    cesium iodide
  56. what is the fluorscopic tube mA range
    .5-5.0 mA
  57. the minimum source to skin distance for stationary flouoroscopy is _____ inches
  58. the minimum source to skin distance for general radiography is ____ cm
  59. the minimum source to skin distance for mobile fluorscopy (c-arm) is _____ in
  60. what is the charge of the electrostatic lenses
    the output phosphor screen is composed of a layer of _____
    • positive
    • zinc cadmium sulfide
  61. the photocathode layer is composed ____
    cesium and antimony compounds
  62. what is the primary function of fluoroscopy
    is to perform dynamic studies to visualizethe motion of internal structures and fluids
  63. how does fluoro work
    after beam exits patient it strikes the input phosphor screen of the II (which absorbs photons to lightthese photons then strike the photocathode layer which is in contact with the input screen (also absorbs light photons and emits electrons)electrons are shot thru the II from photocathode and strike the anode and output screenthen output screen absorbs electrons and emits light photons (50-75x as many more light photons now created)
  64. the tabletop exposure rate on a patient should not exceed ____R/min during fluoro
  65. During a five minute fluoro how much radiation does a pt recieve
  66. when using the c arm where is it safer to stand and where is scatter produced more at
    • safer to stand at the image intensifier side of the tube
    • scatter is produced more at the xray tube side
  67. describe the advantage of imaged intensified fluor over conventional screen flouro
    the advantage was that the radiologists could view the fluoro in brighter light and the images were transmitted onto a video camera and monitor system instead of the image being reflected on mirrors
  68. what is the purpose of the anode in the II
    it attracts electrons because the anode has positive charge and they attract to accelerate from the photocathode through the anode and onto the output phosphor screen
  69. define flux gain
    a simple word for flux and minification are
    • a measurement in the increase of light due to the conversion efficency of the output screen
    • light
    • this gives it the ability to of the phosphor to emit as much light per xray photon
    • electrons
  70. what is minification gain
    how do you calculate it
    • it occurs as a result of the same number of eletrons that were produced at the large input screen being compressed into a small area at the output screen
    • this causes an increase in brightness or intensity of an image
    • minification gain = input screen diameter(squared)/output screen diameter (squared)
  71. formula for total brightness gain:
    minificication gain x flux gain
  72. what is a magnification tube used for
    to make an area bigger that radiologist is viewing this happens by the focal spot (point were electrons meet in II) moving closer to the inout screen by an increase of voltage
  73. what is ABC
    this is like what other system ____
    it does how
    • automatic brightness control is used to automatically maintain satisfactory fluorscopic image density and contrast and brightness
    • AEC
    • because it maintain this brightness of the image automatically by adjusting the exposure factors as necessary to according to subject density and contrast (body part the fluoro is over)
    • adjusts through kvp ma and time
  74. lag:
    defined as the persistence of luminescence (light) after xray stimulation has been terminated
  75. Distortion in fluoro is caused by ____
  76. shape distortion in fluoro is caused by _____
    a geometric problem in the shape of the image intensification tube
  77. high signal to noise ratio is ___
  78. what is vignetting and what is it known as
    this results in what?
    • a fall off in brightnes at the periphery of an image
    • pincushion distortion
    • a better resolution brighter image and less geometric distortion at the center of the image intensifier screen
  79. quantum mottle
    • blotchy or grainy appearance caused by insufficient radaition to create a uniform image
    • increase flouor tube mA  
  80. what are the two different viewing systems that are coupled to the output phosphor screen of the II
    • Mirror optics
    • videos system (television monitoring system)
  81. which viewing system is more common today and differentiate between the mirror optics and video system
    • video system is more common
    • mirror optics uses a series of lenses and mirrors tht magnify the image to a viewer
    • video system is a closed circuit with all transmission thru cables to avoid broadcast interference. It uses a video camera attached to the image intensification tube output phosphor and a display monitor for viewing
  82. what are the different types of systems used to record fluorscopic image
    differenctiate between the two
    • cine and spot film
    • cine consists of a movie camera positioned to intercept the mage produced by the output screen
    • spot film are used to take static xrays for permanent record of the fluoroscopic exam desired for document findings
  83. what is the horizontal line pattern called in the camera atached to the II
    raster pattern
  84. how do we protect ourselves during flouoro
    • wearing a lead apron of at leas .5mm pb/eq
    • must not turn your back towards the fluoro
    • stand behind the radiologist
    • lead drapes over fluoro
    • bucky slot cover
    • stay far from beam as possible
  85. what is the ability to perform dynamic studies to visulaize the motion of internal structures and fluids