The AAPM/RSNA Physics Tutorial for Residents

Computed tomography (CT) is a method of acquiring and reconstructing the image of a thin cross section on the basis of measurements of attenuation. In comparison with conventional radiographs, CT images are free of superimposing tissues and are capable of much higher contrast due to elimination of scatter. Most of the developments in CT since its introduction can be considered as attempts to provide faster acquisition times, better spatial resolution, and shorter computer reconstruction times. From the early designs, the technology progressed with faster scanning times and higher scanning plane resolution, but true three-dimensional (3D) imaging became practical only with helical scanning capabilities. The recent advent of multiple-row detector helical scanners has the capability to produce 3D images that approach the ideal of a true “3D radiograph.” Current multiple-row detector scanners can scan 40-cm volume lengths in less than 30 seconds with near-isotropic resolution and image quality that could not ...