X-ray computed tomography (CT) is a medical imaging technique that produces images of transaxial planes through the human body. When compared with a conventional radiograph, which is an image of many planes superimposed on each other, a CT image exhibits significantly improved contrast although this is at the expense of reduced spatial resolution. A CT image is reconstructed mathematically from a large number of one-dimensional projections of the chosen plane. These projections are acquired electronically using a linear array of solid-state detectors and an x-ray source that rotates around the patient. X-ray computed tomography is used routinely in radiological examinations. It has also been found to be useful in special applications such as radiotherapy treatment planning and three-dimensional imaging for surgical planning.