5. CT-Scanners

This article provides an overview of X-ray imaging techniques used in conventional radiology. Although CT is an X-ray imaging technique, in practice CT-scanners are sufficiently special to warrant a specific presentation. The main reason is the speed at which the source + detector assembly must rotate around the patient (3 rotations per second (200 rotations per minute) is the current limit, resulting in highly complex mechanics), in order to obtain 3D images with minimal motion effects. Consequently, CT scanners use very powerful sources (5 to 9 MHU, 100 kW) and extremely fast detectors (up to 3,000 fps: an order of magnitude faster than the fastest radiology detectors). The detectors are cylindrical in shape, made up of a scintillator with a very low afterglow level (less than 0.1% after 3 ms, less than 0.005% after 50 ms), the pixels are large (typically 0.6 mm), and an electronic chain...