RT207 - NOTES4

• • most frequent used system
  • consists of two sets of rails mounted to the ceiling directly over the radiographic table.

  1. CEILING SUPPORT
• Two sets of two-rails are mounted perpendicular to each other so that the tube can move longitudinally along the length of the table and transversely in a perpendicular direction to the length of the table.
• • When x-ray tube is centered above the examination table at the standard SID, the x-ray tube is in a preferred detent position.
• Has a single column with rollers at each end, one attached to a ceiling-mounted rail and other attached to a floor-mounted rail.

  2. FLOOR-TO-CEILING SUPPORT SYSTEM
• • Interventional radiology suites often are equipped with _____

  3. C-ARM SUPPORT SYSTEM
• guards against excessive radiation exposure and electric shock.

  PROTECTIVE HOUSING
• x-rays emitted through the window

  USEFUL BEAM
• X-rays that escape through the protective housing

  LEAKAGE RADIATION
• A proper design protective housing reduces the level of the leakage radiation to less than _____ when operated at maximum condition.

  100mR/hr at 1m
• • The protective housing around some x-ray tubes contains ___
  • serves both an ____ against electric shock and a;
  • ______ to dissipate heat

  OIL

  INSULATOR

  THERMAL CUSHION
• • maintains a vacuum inside the tube. This vacuum allows for more efficient x-ray production and longer tube life.
  • 30 to 50 cm long and 20 cm in diameter a size of x-ray tube.


  3. GLASS/ METAL ENVELOPE OF ENCLOSURE
• • able to withstand the tremendous heat generated.

  PYREX GLASS
• As a glass enclosure ages, some tungsten vaporizes and coats the inside of the glass enclosure. This alters the electrical properties of the tube, allowing tube current to stray and interact with the glass enclosure; the result is ______

  Arching and tube failure
• • area of tube window.

  5 cm^2
• 1. Cathode
  2. Anode

  INTERNAL COMPONENTS
• • negative side of the x-ray tube.

  Cathode
• COMPONENTS OF CATHODE

  Filament

  Focusing cup
• • Is a coil of wire similar to that in a kitchen toaster, except much smaller.
  • Approximately 2mm in diameter
  • 1 or 2 cm long
  • Made of THORIATED TUNGSTEN.


  Filament
• melting point of thoriated tungsten

  3410 C
• melting point of tungsten

  3400 C
• The addition of _______ to the tungsten filament increases efficiency of thermionic emission and prolongs tube life.

  1% TO 2% THORIUM
• an x-ray tube filament emits electrons when it is heated.

  THERMIONIC EMISSION
• The filament is embedded in a metal cup

  FOCUSING CUP
• • the electron beam is spread beyond the anode because of mutual electrostatic repulsion among the electrons.


  W/O FOCUSING CUP
• which is negatively charged, the electron beam is condensed and directed to the target.


  W/ FOCUSING CUP
• • the focusing cup is the grid and therefore the exposure switch. Designed to be turned on and off very rapidly.

  GRID-CONTROLLED X-RAY TUBE
• the tube current is adjusted by controlling the ______.

  FILMANET CURRENT
• CLOUD OF ELECTRONS called a

  SPACE CHARGE
• difficult for subsequent electrons to be emitted by the filament because of the electrostatic repulsion

  SPACE CHARGE EFFECT
• At a given filament current, tube current reaches a maximum level

  SATURATION CURRENT
• • SATURATION CURRENT is not reached at a lower kVp because of space charge limitation. When an x-ray tube is operated at the saturated current, it is said to be emission limited.
• • most diagnostic x-ray tube has two focal spots, one large and other small.


  DUAL FOCUS
• is used when better spatial resolution is required.

  SMALL FOCAL SPOT
• • range from 0.1 to 1mm.


  SMALL FOCAL SPOT
• • is used when large body parts are imaged and when other techniques that produce high heat are required.

  LARGE FOCAL SPOT
• • range from 0.3 to 2mm


  LARGE FOCAL SPOT
• • positive side of the x-ray tube
  • conducts electricity and radiates heat and contains the target.


  ANODE
• COMPONENTS OF ANODE

  ROTOR

  STEM

  TARGET
• 2 TYPES OF ANODE

  STATIONARY ANODE

  ROTATING ANODE
• • x-rays tubes are used in dental x-ray imaging system
  • some portable imaging system and other special purpose units in which high tube current and power are not required.

  STATIONARY ANODE