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CT Scanner Detection system

CT Scanner Detection system. CT Scanner. Generator High frequency, 30 - 70 kW X-ray tube Rotating anode, high thermal capacity: 3-7 MHU Dual focal spot sizes: about 0.8 and 1.4 Gantry Aperture: > 70 cm of diameter Detectors: gas or solid state; > 600 detectors

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CT Scanner Detection system

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  1. CT Scanner Detection system

  2. CT Scanner • Generator • High frequency, 30 - 70 kW • X-ray tube • Rotating anode, high thermal capacity: 3-7 MHU • Dual focal spot sizes: about 0.8 and 1.4 • Gantry • Aperture: > 70 cm of diameter • Detectors: gas or solid state; > 600 detectors • Scanning time: <1 s, 1 - 4 s • Slice thickness: 0.5 - 10 mm • Spiral scanning: up to 1400 mm

  3. Gas detector (xenon) • Fast detection response • High Sensitivity • Stability against Radiation damage • Stability against Temperature & Humidity • Higher Dynamic range • But less Quantum efficiency • Inherent collimation • Total DQE(Detective Quantum Efficiency) • = 60 percent

  4. Solid detectors • (Ultra Fast Ceramics) UFC • Godalinium OxiSulphade has uniform sensitivity and fast response time • Need collimation so: • Less Geometric Detection Efficiency (GDE) • Total DQE(Detective Quantum Efficiency) • = 80 percent

  5. MTF of CT detectors • MTF depends on Geometric characteristics and size of detector • Also depends on time response of the detectors: • It may be effected by Cross Talk from adjacent projections or Slices due to long Decay time • In new systems Decay time is about 3 s • Afterglow is about 10-4 after 3mS • Design type and construction of detector arrays, detector separation and distance is also important for MTF

  6. number=1000×(mpixel-mwater)/mwaterDetector Calibration CT CT Projections and Reconstruction

  7. Window width & window level

  8. CT scanner Image processing: • Reconstruction time: • 0.5 - 5 s/slice • Reconstruction matrix: 256x256 – 1024x1024 • Reconstruction algorithms: • Bone, Standard, High resolution, etc • Special image processing software: • 3D reconstruction • Angio CT with MIP • Virtual endoscopy • CT fluoroscopy

  9. Introduction to Reconstruction

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