Dmi 100 Review Physics and equipment

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swtjo3joe
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185769
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Dmi 100 Review Physics and equipment
Updated:
2012-12-02 17:05:10
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autotransformer rectifier fluoroscopy pixels CR DR image intensifier bremsstrahlung characteristics
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Physics and equipment
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  1. In many cases, digital fluoroscopy eliminates which of the following?
    postprocedure "overheads" films
  2. a photostimulable phosphor is the active component of what piece of equipment?
    computed radiogrophy imaging plate
  3. in computed radiography, the image must be turned into digital form by what device?
    analog-to-digital converter
  4. a mathematical formula used to reconstruct the image in digital imaging is called?
    an algorithm
  5. picture elements in a digital image are called
    pixels
  6. a digital image is composed of rowns and columns known as a
    matrix
  7. direct digital radiography differs from computed radiography in what way?
    the use of fixed detectors that communicate directly with the computer
  8. window width in CR and DR controls what image property?
    contrast
  9. a graphic display that is constructed to show the radiographer the distribution of pixel values is called
    a histogram
  10. the law stating that the outer shell of an atom can contain no more than eight electrons is called
    octet rule
  11. electromagnetic radiation travels in bundles of energy called
    photons
  12. x-rays travel at what speed?
    • speed of light
    • 186,000 miles per second
  13. waves of radiation are called
    sine waves
  14. wavelength is defined as the distance from
    peak to peak of the wave
  15. frequency is defined as the
    number of waves passing a point per unit time
  16. wavelength and frequency have a what type of relationship?
    inverse proportion
  17. the x-ray beam will change as it travels through the patient by a process called
    attenuation
  18. what are the two types of electromagnetic induction?
    • self-induction
    • mutual induction
  19. self-induction is used in the operation of what device?
    autotransformer
  20. electricity is supplied to the imaging department by a
    generator
  21. the electricity provided to the radiology department is
    60Hz AC
  22. the electricity provided to the radiology department operates at?
    120 pulses per second
  23. high-frequency power
    has almost no ripple
  24. the primary advantage of three-phase power is that
    voltage never drops to zero
  25. a variable transformer that is used to select kVp for the x-ray circuit is the
    autotransformer
  26. a transformer that has more turns in the secondary than in the primary coil is called a
    step-up transformer
  27. voltage coming to the x-ray machine is kept constant through the use of a
    line voltage compensator
  28. where does thermionic emission occur
    cathode
  29. what device is prereading
    kVp meter
  30. what device reduces voltage and provides current to produce an electron cloud or space charge at the filament?
    step-down transformer
  31. what changes AC to DC?
    rectifier
  32. what is surrounded by a negatively charged focusing cup?
    filament
  33. what is composed of solid state, silicon-based diodes?
    rectifier
  34. what measures tube current?
    mA meter
  35. what device spins at 3,300 to 10,000 rpm?
    anode
  36. what is the source of bremsstrahlung and chracteristic rays?
    anode
  37. what is the most commonly used AEC?
    ionization chamber
  38. activating the rotor will
    reduce tube life
  39. the process of thermionic emission causes
    electrons to boil off the filament
  40. the electron stream passes from the cathode to anode because of ______ passing through the x-ray tube
    current
  41. heat is produced in the x-ray tube as
    electrons interact with the target material
  42. most of the energy conversion in the x-ray tube produces
    heat
  43. what percentage of energy in the x-ray tube is converted to x-rays?
    1%
  44. the xray beam is homogenous or heterogenous?
    • heterogeneous or polyenergetic
    • consists of many different energies (wavelength)
  45. what is total filtration?
    • not less than 2.5 mm aluminum equivalent
    • inherent filtration- glass envelope, tube housing, oil
    • added filtration - aluminum
  46. what type of chart may be consulted to determine the safety of a single x-ray exposure?
    tube rating chart
  47. what type of chart may be consulted to determine the safety of a series of x-ray exposures?
    anode cooling curve
  48. the portion of the image-intensifier tube that converts visible light to an electronic image is the
    photocathode
  49. the input phospor of the image-intensifier tube converts
    x-ray energy to visible light
  50. total brightness gain achieved using an image intensifier equals:
    flux gain times minification gain
  51. single phase, full-wave rectification produces:
    pulsating direct current with 120 pulses per second and 100% ripple
  52. three-phase, six pulse full-wave rectification produces:
    direct current with 13% ripple
  53. three-phase, twelve pule full-wave rectification produces:
    direct current with 4% ripple
  54. the increase in average photon energy when using three-phase, six pulse equipment compared with single-phase equipment is:
    35%
  55. the increase in average photon energy when using three-phase, 12 pulse equipment compared with single-phase equipment is:
    41%
  56. the collimator must be accurate to a level of:
    2% of SID
  57. kVp must be accurate to within
    4
  58. exposure linearity must be accurate to within
    10%
  59. exposure reproducibility must be accurate to
    5%
  60. when a spinning top test is performed on single-phase equipment, a radiograph exhibiting four dots would indicate:
    an accurate timer, if set on 1/30sec
  61. when a spinning top test is performed on three-phase equipment, a timer setting of 1/60sec should indicate the following on the resultant radiograph:
    a 6-degree arc
  62. the test that measures the accuracy of adjacent mA stations is
    exposure linearity
  63. the test that measures the accuracy of successive exposures is
    exposure reproducibility
  64. automatic exposure controls may be tested using:
    phantoms
  65. the amount of mA used for fluoroscopy is
    3 to 5
  66. marks on the focal track of the anode resulting from bombardment of electrons are called
    pitting
  67. what is the shortest time with an AEC
    1 ms = 0.001
  68. what does the falling load generator do?
    calculates the most efficient method of obtaining the required mAs
  69. 100% ripple results from which unit containing what type of rectification?
    full-wave rectification for single-phase generator with 4 diodes
  70. 13% ripple results from rectification of which unit?
    three phase, six-pulse
  71. 4% ripple results from rectification of which unit?
    three phase, 12 pulse
  72. 1% ripple results from rectification of which unit?
    high-frequency unit
  73. where are the filaments located in the x-ray tube?
    cathode side
  74. where are the electrons "boiled off" of during exposure?
    filaments
  75. what does the focusing cup do?
    • surrounds the filaments on three sides
    • has negative charge
    • concentrate electrons boiling off the filaments into a narrower stream and repels them toward the anode
  76. what element are the filaments made up of?
    • tungsten
    • because of its high boiling point
  77. how fast does the anode rotate?
    3300 to 10,000 rpm
  78. what controls the rotation of the anode?
    induction motor located outside the x-ray tube
  79. what does the target angle of the anode accomplish?
    allows for a larger actual focal spot while producting a smaller effective focal spot
  80. what is the actual focal spot?
    area bombarded by electrons
  81. what is the effective focal spot?
    area seen by the image receptor
  82. what is the "line focus principle"?
    • the larger the actual spot, the greater the heat capacity
    • the smaller the effective focal spot, the greater the radiographic image sharpness
  83. how many degrees can a target angle of an anode be?
    7 to 20 degrees depending on tube design
  84. what does the glass envelope contain?
    • cathode and target
    • vacuum
    • tube window
  85. Describe how x-rays are created step by step
    • the x-ray machine is turned on, and a small amount of current is sent to the filament to warm it and ready it for much higher current
    • radiographer takes equipment through warm up exposures to further warm the filament and the anode
    • radiographer chooses exposure factors on control console for the exam to be performed
    • electricity coming into the the radiology department is adjusted by the line voltage compensator in the x-ray equipment to maintain it at a constant level
    • when making the exposure, the radiographer presses the rotor switch and exposure switch in one continuous motion
    • the induction motor begins spinning the anode as the filament gets hotter
    • when the eposure switch is closed, the voltage selected by the mA control flows from the autotransformer, through the variable resistors, and into the step-down transformer in the filament circuit
    • the filament heats considerably, boils off electrons (thermionic emission), and creates a space charge or electron cloud aroud the filament
    • at the same time, the alternating current and voltage the radiographer selects by choosing taps off the autotransformer are sent to the primary coils of the high-voltage step-up transformer, where they are boosted to kilovoltage levels
    • after leaving the secondary coils of the step-up transformer, the voltage and alternating current are sent through the rectifier, which changes the alternating current to pulsating direct current
    • the kilovoltage creates a high potential difference in the x-ray circuit, making the anode less negative (relatively positive) and the cathode highly negative
    • this high potential difference causes the electrons to move at very high speed (approximately half the speed of light) from the cathode to the anode
    • the collision of these projectile electrons with the atoms of the target material causes a conversion of the electrons' kinetic energy (100%) to heat (99.8%) and xrays (0.2%)
    • heat is produced when the projectile electrons strike the outer shell electrons of the target material and place them in an excited state, which causes them to emit infrared radiation
    • the production of x-rays comes from two interactions with the anode
  86. what are bremsstrahlung xrays?
    xrays formed by a projectile electron missing an outer shell electron in the target and moves in close to the nucleus where it is slowed down (braking) due to repulsion (nucleus is positive and the electron is negative) thus releasing energy in the form of xrays
  87. at diagnostic levels, most xrays are produced from what type of interaction? Bremsstrahlung or characteristic?
    brems
  88. what are characteristic xrays?
    • a projectile electron collides with an inner shell electron of a target atom
    • it removes that electron from orbit and ionizes the atom
    • a hole exists in the inner shell from the vacated electron
    • an electron from an outer shell falls in to fill the hole and releases energy
  89. what determines a characteristic xray's energy?
    it is equal to the difference in the binding energies of the shells involve
  90. xrays produced from which shell of an atom are of sufficient energy to be used in radiography?
    k shell
  91. at what kvp level are characteristic xrays produced?
    • above 70
    • only in small number
  92. what does the input phosphor do?
    convert xray energy to visible light
  93. what does the photocathode do?
    • converts visbile light, converted by the input phosphor, into electrons
    • it releases electrons in amounts directly proportional to the visbile light striking it
  94. what are the components of an image intensifier? name the parts in order starting from when xrays first hit it
    • input phosphor
    • photocathode
    • focusing lens
    • output phosphor
  95. what does the output phosphor do?
    • convert electrons from the photocathode into visbile light 50 to 75 times greater
    • known as flux gain
  96. what is minification gain?
    the output phosphor is smaller than the input phosphor, resulting in an increase in brightness
  97. how do you calculate the total brightness gain?
    minification gain x flux gain
  98. how is magnification made possible in fluoroscopy?
    by varying the voltage flowing through the image-intensifier tube, this changes the size of the area on the input phosphor/photocathode being used
  99. how do you calculate the heat units for a single-phase, full-wave rectified equipment
    kvp x mAs
  100. how do you calculate the heat units for a three-phase, six pulse, full-wave rectified equipment?
    • kvp x mAs x 1.35
    • (remember this equipment produces x-ray photons with 35% higher average photon energy
  101. how do you calculate the heat units for a three-phase, 12 pulse, full-wave rectified equipment?
    kvp x mAs x 1.41

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