IR SECOND QUIZ

• X-RAY GENERATOR

  —     a device that acts as the primary control mechanism for the entire fluoroscope.

  —      It is through the X-ray generator that current is allowed to flow into the X-ray tube.
• The basic function of adjusting the voltage differential and current of the X-ray tube are controlled automatically to maintain optimal contrast and brightness
• —     X-rays may be generated in either a continuous or a pulsed mode.
• —     Automatic brightness control is a standard feature of the majority of modern fluoroscopes. Through this system mA and kVp are constantly monitored and adjusted to optimize the image. 
• X-RAY TUBE 

  —     Functions as a specific energy converter,

  —     receiving electrical energy and converting it into two other forms of energy:

  x-radiation (1%) and

  heat (99%).
• —     Heat is considered the undesirable product of this conversion process; therefore x-radiation is created by

  —     taking the energy from the electrons and converting it into photons.

  —     ELECTRONS TO PHOTONS:

  —     This very specific energy conversion takes place in the x-ray tube. 
• CATHODE (━)

  ·       negative side of the x-ray tube;

  ·       it has two primary parts, a filament and a focusing cup. 

  • · The two filaments supply separate electron beams to produce two focal spots.
• Filament 

  ·       Is a coil of wire similar to that in a kitchen toaster, but it is much smaller. 

  ·       Approximately 2 mm in diameter and 1 or 2 cm long. 

  ·       Emits electrons when it is heated. 
• When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are “boiled off” and ejected from the filament. This phenomenon is known as THERMIONIC EMISSION. 
• Focusing Cup 

  ·       The filament is embedded in a metal shroud called the focusing cup 

  ·       Because all of the electrons accelerated from cathode to anode are electrically negative, the electron beam tends to spread out owing to electrostatic repulsion. 

  ·        Some electrons can even miss the anode completely. 
• ANODE (+)

  ● Is the positive side of the x-ray tube 

  ● It conducts electricity 

  ● Radiates heat 

  ● Contains the TARGET 
• TARGET - o Area of the anode struck by the electrons from the cathode

  FUNCTIONS

  o   Conducts electrons from the cathode 

  o   Mechanical support for the target 

  o   Thermal dissipater 
• IMAGE INTENSIFIER

  ·       Complex electronic device that receives the image-forming x-ray beam and converts it into a visible-light image of high intensity 
• Input phosphor = Cesium iodide (CsI) 
• Output phosphor 

  ● Usually made of zinc cadmium sulfide. 

  ● The site where electrons interact and produce light. 
• Electron optics 

  ● Maintaining proper electron travel 

  ● Electrostatic focusing lenses 

  ● Directs the path of electrons towards the anode 
• INPUT PHOSPHOR-X-ray energy is converted into visible light 

  Similar to the effect of radiographic intensifying screens 
• Photocathode 

  ● Usually composed of cesium and antimony compounds that 

  ● Respond to stimulation of input phosphor light by the emission of electrons 

  ● The photocathode emits electrons when illuminated by the input phosphor. 

  ● Photoemission - electron emission that follows light stimulation. 
• The lenses and the mirror in the TV lens system must remain precisely adjusted to avoid a blurred image
• The objective lens accepts light from the output phosphor and converts it into a parallel beam
• An image recorded on film is interrupted by a beam-splitting mirror
• The beam-splitting mirror transmits only a portion of the beam to the television camera
• The beam-splitting mirror is retracted from the beam when a film camera is not in use
• Both the television camera and the film camera are coupled to lenses that focus the parallel light beam onto the film and target of the respective cameras
• TV camera IS Used to electronically convert the visible image on the output phosphor of the image intensifier.
• The television camera consists of cylindrical housing, approximately 15 mm in diameter by 25 cm in length, that contains the heart of the television camera tube.
• TV CAMERA - It also contains electromagnetic coils that are used to properly steer the electron beam inside the tube. A number of such television camera tubes are available for television fluoroscopy, but the vidicon and its modified version, the Plumbicon, are used most often.
• The video signal received by the television picture tube is modulated, that is, its magnitude is directly proportional to the light intensity received by the television camera tube.
• Different from the television camera tube, the electron beam of the television picture tube varies in intensity according to the modulation of the video signal
• ·       The intensity of the electron beam is modulated by a control grid, which is attached to the electron gun.

  This electron beam is focused onto the output fluorescent screen by the external coils
• Photographic Subtraction Technique

  ⚫  Introduced by Ziedses des Plantes, a technique by which bone structure images are subtracted, or cancelled out, from a film of the bones plus opacified vessels, leaving an unobscured image of the vessels
• ⚫  Zero Film or base or control film – shows bony structures only, no patient motion must be present in this film. Zero film is exposed just before contrast medium is injected into vessels
• ⚫  Series film – contains image post-injection of contrast material
• ⚫  Registration - matching of one image over another so that bony landmarks are precisely superimposed
• 1. ray generator is the primary control mechanism for the entire fluoroscope
• Current flows into the X-ray tube through the X-ray generator
• 1. ray generator automatically adjusts the voltage differential and current of the X-ray tube to maintain optimal contrast and brightness
• High-frequency generators provide superior exposure reproducibility, compact size, lowest purchase price, and lowest repair costs
• 1. rays can be generated in either continuous or pulsed mode
• Automatic brightness control is a standard feature in modern fluoroscopes