special subjects
Computed Tomography (CT)
Procedure for CT
For CT, a person lies on a motorized table that is moved through the opening of a doughnut-shaped scanner. The person is moved through the scanner as these devices rotate around the person. For some CT scans, the table moves incrementally and stops when each scan (slice) is taken. For other CT scans, the table moves continuously during scanning. Because the person is moving in a straight line and the detectors are moving in a circle, the series of measurements appear to be taken in a spiral fashion around the person. People should wear clothing that has no metallic buttons, snaps, zippers, or other metal in it over the area to be scanned and should remove any jewelry. Such items are not dangerous but may block x-rays and distort the image. During the test, people must remain still and periodically hold their breath when the x-rays are taken so that the images are not blurred. People may hear whirring sounds during the procedure. The procedure, depending on the area examined and how modern the scanner is, usually takes from only a few seconds to a few minutes. CT of the chest takes less than a minute, and people have to hold their breath only once and only for a few seconds. For CT, people may be given a Radiographic Contrast Agents . Contrast agents are substances that can be seen on x-rays and help distinguish one tissue from another. The contrast agent may be injected into a vein, taken by mouth, or inserted through the anus. The contrast agents used depends on what type of test is done and which body part is being evaluated. CT is usually done as an outpatient procedure. People can resume their usual activities immediately after the test. In computed tomography, a scanner produces and records x-rays as it rotates around a person, who is moved through the scanner on a motorized table. On one side of the scanner is an x-ray tube, which produces x-rays, and on the other side is an x-ray detector. 