Mrt 215

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  1. What components are located in the CT gantry?
    The gantry houses the imaging components such as the x ray tube, high tension generator(a small solid state, high frequency generator), collimators, detectors(detector array),and detector elecronics(also known as Data acquision systemD.A.S)
  2. Major components of CT
    • Gantry
    • Patient couch(table)
    • Image display
    • Operator's console for computer system (image acquisition recording storage)
  3. Gantry
    Frame maintains alignment of tube and detectors.
    • Generator
    • tube
    • Detectors
    • Digital acquisition system (DAS)
    • Cooling system
  4. DAS (digital acquition system)
    • Data acquistion system
    • Located between the detector and computer
    • pre amplifier- analog signal from the detector is amplified
    • ADC- Most are 16 bit
    • Transmits this data to the computer
  5. Gantry
    Can be bertical or angled(tilted +-30degrees)
  6. Psitioning lights
    • White halogen or red laser
    • 3 lights
    • Sagital
    • Cornal
    • Transverse
  7. Cooling system
    draws in air from the room, cools the electrical components warmed by the heat generated by the x-ray tube, warm air then expelled through filters at the top of the gantry
  8. data acquisition system
    3 functions: measures transmitted radiation beam (logarithmic amplifier), encodes these to binary data (ADC) and transmits binary data to the computer Most CT ADC are 16 bit Tube rotates around slip rings- low voltage- mains supplied to the slip ring, generator and transformer are directly on the spliring rotating with the tube (added weight , additional cooling required, difficulty upgrading)There use to be the generator outside of the gantry, then would have a high voltage slip ring (use a gas – sulphur hexafluoride to reduce the risk of arcing)- also had a low voltage slip ring for heat exchanger, das fan ect
  9. Ct Xray tube features
    • Rotating anodes
    • High heat load- 0.5 – 5 MHU
    • Pulsed
    • operates at 120 kVp
    • 1-5 msec pulses
    • up to 1000 mA
    • ¡Some 80-140 kVp
    • Anode = layered alloyed
    • ¡Tungsten & rhenium
    • Housing = air or liquid cooled
  10. Philips Brillaiance 40 Slice Configuration
    • 40 slices per rotation
    • 40 mm coverage
    • 40 x .625 mm, 32 x 1.23 mm, 16 x 2.5 mm
    • 8.0 MHU MRC X-ray tube
    • 40 images per second reconstruction
    • 60kW Generator
    • 0.4 sec rotation: scan time/rotation
  11. Detectors Two types¡
    • Xenon ionization chambers (obsolete)¡Scintillation
    • ¡Solid state
  12. Scintillation Detectors
    • In conjunction with photomultiplier
    • Converts X-ray photon to lightLight converted into electrical energy
    • Light amplified by photomultiplier
    • At anode electrons converted into digital signal
    • Processed by computer
    • Early generations:
    • ¡Sodium iodide (lag)
    • ¡Calcium fluoride (lag)Bismuth germanate
  13. Solid Sate (scintillation) detector
    • Used in helical & MSCT scanners
    • Similar to DR system detectors
    • Made of:
    • Calcium tungstate
    • Yttrium or gadolinium (ceramic)
    • Scintillator bonded to top of photodiode
    • X-ray photon causes crystal to fluoresce
    • Photodiode transforms light to electrical (analog) signal
    • Detector on circuit board (very close)
    • Allow for large angles of X-ray beam (permits fan-shaped beam)
    • Increased sensitivity
  14. Detector Characteristics
    • High capture efficiency: receive photon from patient
    • Controlled by detector size & distance between detectors
    • High absorption efficiency: converts incoming x-ray
    • ¡Determined by detector: material, size & thickness
    • High conversion efficiency
    • Converts absorbed photon to digital signal
    • Equals= detector dose efficiency
  15. List features of a CT table
    • Low-density composite
    • -carbon-graphite
    • Programmed indexing
    • Horizontal movements
    • Height adjustable
    • Weight limit up to 600lbs
  16. CT Console
    All image acquisition and exposure parameters can be set on the CT control console
  17. Parameters on the control console
    • —On/off switch
    • —Technical factor selection –kV, mA
    • —Scan time
    • —Slice thickness
    • —Display matrix dimensions (DFOV)
    • —Scan area
    • —Window width & levelData entry (pt info)

    • —Image manipulation
    • —Archiving
    • —Gantry & couch controls
    • —Algorithms
  18. CT Computer System
    • Operates image acquisition
    • Tube
    • Detectors
    • Collimation
    • Displays and Archives images
    • Post-processing capabilities

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Mrt 215
2012-02-11 21:36:17

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