CAT scan: Computerized axial tomography scan. CAT scanning is a painless X-ray test in which a computer generates cross-section views of a patient's anatomy. It can identify normal and abnormal structures, and it can be used to guide procedures. Contrast material is sometimes used in CAT scanning. A patient who is allergic to iodine or contrast materials and is scheduled to have a CAT scan should notify the physician and the radiology staff about the allergy. Also known as CT scan.