1. CT Scanner Detection system

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

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

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

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

6. Detector Calibration number=1000×(  pixel-  water)/  water Detector Calibration CT CT Projections and Reconstruction

7. 7 Window width & window level

8. 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 9