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CT Data Acquisition

Ch. 5 CT Physics Seeram, 3rd edt.

first generation scanners parallel beam, translate-rotate scanning. used fixed-anode, oil-cooled tubes.
second generation scanners fan beam, translate-rotate. used fixed-anode, oil-cooled tubes.
Third generation scanners fan beam, rotate-rotate. ring artifacts.
Fourth generation scanners fan beam, fixed detectors.
4th generation: 2 beam geometries 1) rotating fan beam within circular detector array 2) rotating fan beam outside nutating detector ring
Slip Ring allows continuous gantry rotation. 2 designs: disk and cylinder.
Low voltage slip ring 480 AC power to ____ to high voltage generator to x-ray tube.
High voltage slip ring AC to high voltage generator to _____ to x-ray tube. generator does not rotate with tube.
5th generation scanners EBCT and DSR (dynamic spatial reconstructor). high speed.
EBCT fan beam produced by a beam of electrons. detector tungsten is stationary. 3D imaging. Boyd.
6th generation dual source ct scanner (cardiac imaging). 2 tubes, 2 detectors 90* apart.
7th generation flat panel digital detectors. prototype development. angiography and breast imaging.
High Frequency X-Ray Generator is _____. small, compact, efficient, inside gantry. ripple less than 1%.
Anode rotating, heterogeneous beam.rapid heat dissipation.
Anode Target Rhenium, tungsten, and molybdenum
Glass envelope tubes vacuum, structural support, high voltage insulation. internal getters (ion pumps). electrical arcing from tungsten deposits.
Metal envelope tubes ceramic insulators, larger anode disks, higher tube currents, better heat dissipation.
Cathode 1 or more tungsten filaments in focusing cup. Getter usually made of barium.
Bearing assembly
working life of CT tubes 10,00 to 40,000 hours (1,000 hours for x-ray)
Straton tube designed by Siemens. encased in oil for cooling. consists of anode, cathode, deflection coils, electron beam, motor.
Filtration removes long wavelength x-rays. hardens beam. shapes energy distribution (uniform beam hardening).
where are the 2 main collimators located? pre-patient and pre-detector
which collimator determines slice thickness? pre-detector (post patient)
Name the 6 detector characteristics efficiency, response time, dynamic range, high reproducibility, stability, afterglow
Efficiency Ability to capture, absorb, and convert x-ray photons to electrical signals
Capture efficiency ability to obtain photons from patient. size of the detector are facing beam and distance between two detectors determine this.
Absorption efficiency # photons absorbed by detector. determined by atomic #, physical density, size, and thickness of detector face.
Stability Steadiness of detector response.
Response time speed with which the detector can detect x-ray event and recover to detect another one.
Afterglow persistence of image after radiation is turned off. should be 100 ms.
2 types of detectors Scintillation and Gas Ionization
Scintillation detector convert x-ray energy into light, then electrical energy. solid state, photodiode.
Gas Ionization detector x-ray energy directly to electrical energy. xenon.
multirow detector categories matrix array (isotropic) or adaptive array (anisotropic)
Data acquisition system (DAS) detector electronics positioned between detector array and the computer. 3 functions - measures transmitted radiation beam, encodes measurements into binary data, transmit binary data to computer
16 bit Modern CT scanners use ___ ADC
optoelectronics lens and light diodes to facilitate data transmission.
dynamic range ratio of largest signal to smallest signal measured by detector.
Created by: akel