Computed Tomography (CT) is an imaging test in which a part of the body is X-rayed from different angles. These images are combined by a computer to produce cross-sectional pictures of internal organs. Except for the injection of a dye (needed in some but not all cases), this is a painless procedure that can be done in an outpatient clinic. It is often referred to as a "CT" or "CAT" scan. – American Cancer Society