A CT scan is a diagnostic test that uses both x-ray and computer technology. Cross section pictures of the body are taken and analyzed by the computer to make 3 dimensional pictures of the body. The CT scanner is a large square machine with a hole in the center, something like a doughnut. The procedure takes approximately 20-30 minutes and is painless. During a CT scan, you lie still on a table as it slowly passes through the center of a large X-ray machine. During some tests you receive a contrast dye, which makes parts of your body show up better in the image. Following the procedure you may get back to your normal activity and diet right away.