Mrt 215

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)

• Gantry
• Patient couch(table)
• Image display
• Operator's console for computer system (image acquisition recording storage)

• Generator
• tube
• Detectors
• Digital acquisition system (DAS)
• Cooling 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

Can be bertical or angled(tilted ^+-30degrees)

• White halogen or red laser
• 3 lights
• Sagital
• Cornal
• Transverse

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

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

• 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

• 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

• Xenon ionization chambers (obsolete)¡Scintillation
• ¡Solid state

• 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

• 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

• 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

• Low-density composite
• -carbon-graphite
• Programmed indexing
• Horizontal movements
• Height adjustable
• Weight limit up to 600lbs

All image acquisition and exposure parameters can be set on the CT 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

• Operates image acquisition
• Tube
• Detectors
• Collimation
• Displays and Archives images
• Post-processing capabilities