X-ray Imaging System (Midterms)

Cards (36)

  • Three Principal Parts of X-ray Imaging System
    1. X-ray tube
    2. Operating console
    3. High-voltage generator
  • Operating Console
    • allows RT to control the x-ray tube current and voltage so useful x-ray beam is of proper quantity and quality
    • provides for control of line compensation, kVp, mA, and exposure time
    • located in an adjoining room with a protective barrier separating the two (most systems)
  • X-ray tube
    • located in the examination room
  • High-voltage generator
    • housed in an equipment cabinet positioned against a wall
    • always close to the x-ray tube, usually in the examination room
    • responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production
  • Radiation quantity
    • number of x-rays or the intensity of the x-ray beam
    • expressed in milligray (mGya) or milligray/milliampere-second (mGya/mAs)
  • Radiation quality
    • penetrability of the x-ray beam
    • expressed in kilovolt peak (kVp) or half-value layer (HVL)
  • Meters
    • provided for monitoring kVp, mA, and exposure time
  • 220 V power
    • V power that most x-ray imaging systems are designed to operate
    • some are 110 V or 440 V
  • 5%
    • voltage provided to an x-ray unit may vary by as much as this percent
  • Line Compensator
    • measures the voltage provided to the x-ray imaging system and adjusts that voltage to precisely 220 V
  • Autotransformer
    • has a single winding and is designed to supply a precise voltage to the filament circuit and to the high-voltage circuit of the x-ray imaging system
    • where power supplied to the x-ray imaging system is first delivered
    • works on the principle of electromagnetic induction but is very different from the conventional transformer
    • can be designed to step up voltage to approximately twice the input voltage value
  • Primary connections
    • A and A' conduct the input power to the autotransformer
    Secondary connections
    • C allows autotransformer to increase voltage
    • D and E allow a decrease in voltage
  • Primary voltage
    • voltage it receives
    • operated by autotransformer
  • Secondary voltage
    • voltage it provides
    • operated by induction device
  • Autotransformer Law
    • same as transformer law
  • Minor kilovolt peak Selection
    • "fine tunes"
    • represent two separate series of connections on the autotransformer
  • Major kilovolt peak Selection
    • represent two separate series of connections on the autotransformer
  • kVp
    • determines the quality of the x-ray beam
  • 220 V Primary voltage
    • controllable from about 100 to 400
  • kVp Meter
    • placed across the output terminals of the autotransformer and therefore actually reads voltage, not kVp
  • Scale of the kVp meter
    • registers kilovolts because of the known multiplication factor of the turns ratio
  • Pre-reading kVp Meter
    • kVp meter registers, even though no exposure is being made and the circuit has no current
    • allows the voltage to be monitored before an exposure
  • Milliamperes (mA)
    • measure of x-ray tube current, crossing from cathode to anode
  • Temperature of the filament
    • determines the number of electrons emitted by the filament
  • Filament temperature
    • controlled by the filament current
    • measured in amperes (A)
  • 3 to 6 A
    • currents of normally operated filaments
  • Thermionic emission
    • release of electrons from a heated filament
  • Filament circuit
    • separate circuit that controls x-ray tube current
  • Connections
    • provide voltage for the filament circuit
  • Precision resistors
    • used to reduce this voltage to a value that corresponds to the selected milliamperage
    • result in fixed stations that provide tube currents of 100, 200, or 300 mA, and higher
  • mAs
    • product of x-ray tube current (mA) and exposure time(s)
    • also "electrostatic charge (C)"
  • mA meter
    • connected at the center of the secondary winding of the high-voltage step-up transformer
    • how x-ray tube current is monitored
  • Secondary voltage
    • alternating at 60 Hz such that the center of this winding is always at zero volts
  • Filament Transformer
    • "Filament heating isolation step-down transformer"
    • steps down the voltage to approximately 12 V and provides the current to heat the filament
    • Primary windings
    • thin copper and carry a current of 0.5 to 1 A and approximately 150 V
  • Secondary windings
    • thick and approximately 12 V electric potential and carry a current of 5 to 8 A