RT207 - NOTES5

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    • THREE PRINCIPAL PARTS OF X-RAY IMAGING SYSTEM
      X-RAY TUBE
      OPERATING CONSOLE
      HIGH VOLTAGE GENERATOR
      • Part of the x-ray imaging system most familiar with.
      • Allows radiologic technologist to control the x-ray tube current and voltage so that the useful x-ray beam is of proper quantity and quality.
      OPERATING CONSOLE
      • refers to the number of x-rays or the intensity of the beam usually expressed in mR or mGy per mAs.

      RADIATION QUANTITY
    • RADIATION QUANTITY = X-RAY INTENSITY
      • refers to the penetrating quality of the x-ray beam and is expressed by kVp or half value layer.

      RADIATION QUALITY
    • RADIATION QUALITY = X-RAY PENETRABILITY
    • some basic controls that every panel have:
      on/off control
      mAs selection
      kVp selection
      Table or wall unit activation
      exposure switch
      Line compensation
      mA meter
    • Most x-ray imaging systems are designed to operate on 220V
    • incorporates a meter to measure the voltage provided to the x-ray machine and a control to adjust that voltage to precisely 220 volts.
      LINE COMPENSATION
      • designed to supply a precise voltage to the filament circuit and to the high-voltage circuit of the x-ray machine.
      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.
      AUTOTRANSFORMER
      • It is much safer and easier to control a low voltage and then increase it than to increase a low voltage to the kilovoltage level and then control the kilovoltage magnitude.
      • Some older x-ray operating consoles have labelled major kVp and minor kVp, and by selecting a combination of these controls the radiographer can provide precisely the required kVp.

      kVp Adjustment
      • determines the penetrating quality of the x-ray beam
      kVp
      • placed across the output terminals of the autotransformer and therefore reads voltage.
      kVp meter
      • it allows the kilovoltage to be monitored before an exposure
      Pre-reading kVp meter/voltmeter
    • X-ray tube current crossing from cathode to anode is measured in
      mA
    • mA Control
      • The filament temperature is controlled by the filament current, which is measured in ____

      Amperes (A)
    • Filament normally operates at the current between
      3 - 6 Amperes
      • X-ray tube current is controlled through a separate circuit
      Filament Circuit
      • Xray tube current normally is not continuously variable. Precision resistors result in fixed stations that provide x-ray tube currents of 100, 200, or 300 mA and higher. Except __________

      when falling load generator happens.
      • exposure begins at maximum mA, and the mA drops as the anode heats which results to minimum exposure time.

      Failing Load Generator
      • The filament transformer is a step-down transformer; therefore voltage supplied to the filament is lower than the voltage supplied to the filament transformer.

      Failing Load Generator
      • monitors the x-ray tube current.
      mA meter
      • filament heating isolation step-down transformer
      • It steps down the voltage to approximately 12V and provides the current to heat the filament.
      Filament Transformer
      • Primary windings are thin copper and carry a current of 0.5 to 1A and approximately 150v
      • Secondary windings are thick copper and at approximately at 12 V and carry a current of 5 to 8 A.
    • Device that measures the quantity of radiation that reaches the image receptor
      AUTOMATIC EXPOSURE CONTROL
      • responsible for converting the low voltage from the electric power company into a kilovoltage of the proper waveform.
      HIGH VOLTAGE GENERATOR
    • HIGH VOLTAGE GENERATOR COMPONENTS
      HIGH VOLTAGE TRANSFORMER
      RECTIFIERS
      FILAMENT TRANSFORMER
    • the process of converting alternating voltage into direct voltage and therefore alternating current into direct current.
      RECTIFICATION
    • electronic device that allows current flow in one direction.
      RECTIFIERS
      • Voltage rectification is required to ensure that electrons flow from x-ray tube cathode to anode only.
    • X-RAY TUBE FAILURE:
      Heat can be dissipated in one of three ways:
      RADIATION
      CONDUCTION
      CONVECTION
      • Excessive heat results in reduced x-ray tube life.
    • CAUSE: Excessive anode temperature during a single exposure.
      EFFECT: Localized surface melting and pitting of the anode.
      EFFECT ON RADIOGRAPH: Surface irregularities result in variable and reduced radiation output.
      MANIFESTATION: surface irregularities result in variable and reduced radiation output.
    • CAUSE: Severe surface melting
      EFFECT: Tungsten can be vaporized and can plate the inside of the glass enclosure.
      EFFECT ON RADIOGRAPH: Filtering of the x-ray beam and interference with electron flow from cathode to anode
      MANIFESTATION: Filtering of the x-ray beam and interference with electron flow from cathode to anode
    • SAFE OR UNSAFE TECHNIQUES
      RATING CHARTS
    • THREE TYPES OF RATING CHARTS
      RADIOGRAPHIC RATING CHARTS
      ANODE COOLING CHART
      HOUSE COOLING CHART
      • Most important because it conveys which techniques are safe and unsafe.
      • For a given mA, any combination of kVp and the time that lies below the mA curve is safe.
      • Above, unsafe
      RADIOGRAPHIC RATING CHARTS
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