A CAT (computed axial tomography) scan is a painless test that uses multiple x-ray images, taken from different angles, to create three-dimensional images of body structures. It is sometimes called a CT scan. Increasingly, CAT scans use digital x-rays to produce their images on a computer screen. A cardiologist may order the test to get a clear picture of the heart, the aorta (the main artery carrying oxygen-rich blood from the heart to the rest of the body), the lungs and the coronary arteries. 

In recent years, CAT technology has rapidly advanced, and researchers have developed new uses for the technology. For example, many facilities now use a type of CAT scan called a helical CAT scan, which uses special slip-ring technology to create a continuously moving x-ray tube. Another type of CAT scan is the multislice CAT scan, which creates up to 64 images and allows physicians to look more closely at intricate heart structures.

If the test requires an injection of a special dye (contrast medium) or a sedative, then patients are generally advised not to eat or drink for four to six hours before the test. Otherwise, no special preparation is required. The length of a CAT scan depends upon the needs of the physician and the type of scanner being used. In newer equipment, a CAT scan may take less than one minute (sometimes seconds). Other CAT scans may take as long as an hour.