CT (CAT) scan is a noninvasive medical test. CT imaging combines special x-ray equipment with sophisticated computers to produce multiple images of the inside of the body. These cross-sectional images can then be examined on a computer monitor. CT scans of internal organs, bone, soft tissue and blood vessels provide much greater clarity and reveal more details than regular x-ray exams. Intravenous injection of a special iodine-based dye reveals more information about the tissues, even permitting non-invasive road-maps of the blood vessels, "CT angiograms". This dye may not be safely given in some patients with kidney disease. Also some patients may be allergic to the iodine in the dye. If you have a history of allergic reaction from a previous dye injection, you should check with your doctor prior to the exam.