RT100: CHAPTER 5: THE X-RAY MACHINE

• 1. RAY MACHINE COMPONENTS & PARTS

  • X-ray tube
  • Control console
  • High-voltage section / generator
• 3 PRINCIPAL PARTS


  • X-ray tube
  • Control console
  • High-voltage section / generator
• 1. ray tube


  The component that produces the x-rays
• Control console


  The apparatus that allows the technologist to control the x-ray tube current and voltage
• High-voltage section / generator


  The component responsible for converting the low voltage from the electric power company into a kilo-voltage of the proper waveform
• Protective housing


  • Controls radiation exposure and electric shock
  • Contains the x-ray tube
  • Provides mechanical support and protects the tube from damage
• Useful beam


  1. rays emitted through the window of the protective housing
• Leakage radiation


  1. rays that escape through the protective housing
• Glass envelope


  Contains the components of the x-ray tube and is a special kind of vacuum tube made of Pyrex glass
• Cathode components


  • Filament
  • Focusing cup
• Filament


  A coil of wire that emits electrons when heated, made of thoriated tungsten
• Focusing cup


  Negatively charged to condense the electron beam to a small area of the anode
• Anode types


  • Stationary
  • Rotating
• Stationary anode


  • Used in dental x-ray machines, some portable machines and other special purpose units where high tube current and power are not required
• Rotating anode


  • Used in general purpose x-ray tubes as they must be capable of producing high-intensity x-ray beams in a short time
• Anode parts


  • Target
  • Rotating anode
  • Induction motor
• Target


  The area of the anode struck by the electrons from the cathode, alloyed with tungsten for added mechanical strength
• Rotating anode


  Allows the electron beam to interact with a much larger target area, so the heating of the anode is not confined to one small spot
• Induction motor


  Drives the rotating anode
• Operating console


  Allows the technologist to control the x-ray tube current and voltage to produce a useful beam of proper intensity and penetrability
• Operating console controls


  • Line compensation
  • kVp (kilovolt peak) adjustment
  • mA (milliampere) adjustment
  • Exposure timer
• Line compensation


  Incorporates a meter to measure the voltage provided to the unit and a control to adjust the voltage to precisely 220V
• kVp (kilovolt peak) adjustment


  Adjusts the peak kilovoltage applied to the x-ray tube, which determines the wavelength, penetration ability, and number of shades of gray
• mA (milliampere) adjustment


  Adjusts the x-ray tube current, the number of electrons crossing from cathode to anode per second
• Exposure timer


  Determines the number of x-rays reaching the image receptor, related to both tube current and time the tube is energized
• High voltage section


  Responsible for converting the low voltage from the power company into the kilovoltage required for the x-ray tube
• High voltage section components

  • High-voltage step-up transformer
  • Filament transformer
  • Rectifiers
• Transformer


  Electrical device to alter the magnitude of kVp or mA
• Rectification


  Conversion of AC to DC
• Kinetic energy


  The energy of motion, proportional to mass and the square of velocity
• The distance between the filament and target is only 1-3 cm, requiring intense accelerating force to raise electron velocity
• Projectile electrons


  The electrons traveling from cathode to anode that comprise the x-ray tube current
• Projectile electrons hit the target atoms

  They interact with the atoms and transfer their kinetic energy to the target
• Approximately 99% of the kinetic energy of projectile electrons is converted to heat, only 1% is used to produce x-rays
• Characteristic radiation


  1. rays produced when a projectile electron ionizes a target atom by removing an inner-shell electron, and an outer-shell electron falls into the void
• Bremsstrahlung radiation


  1. rays produced when a projectile electron comes close to the nucleus of a target atom and is deflected by the electric field, resulting in the emission of radiation