Computed tomography (CT) is a modern X-ray-based cross-sectional imaging technique. The patient lies on a table, called a couch, and is moved into a short tunnel, the gantry. Inside the gantry, an X-ray tube rotates around the patient, emitting a thin fan-shaped beam at short intervals. This radiation passes through the body and is measured by detectors on the opposite side. A high-performance computer then calculates predefined cross-sectional images. In modern CT scanners, the tube-detector system can rotate continuously about 1 to 2 times per second (spiral CT), allowing many slices to be captured and displayed within seconds. Computer-assisted post-processing can generate two- and three-dimensional images in all planes. CT is suitable for imaging nearly all body regions. Often, iodine-based contrast agents are injected into a vein to better distinguish blood vessels, tumors, or inflammation from surrounding tissue. For bowel contrast, iodine-based contrast may need to be ingested before the examination. Most CT scans require breath-holding techniques to avoid motion artifacts caused by breathing.