RT207 - NOTES5

• 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