CT Data Acquisition Word Scramble
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| Term | Definition |
| 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
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