According to Johns Hopkins Medicine, a CAT scan, or computed tomography scan, with contrast is a method of imaging the body with X-rays and computer technology during which a particular organ or section of the body is highlighted by a dye that the patient takes orally or has inserted intravenously through an IV line. CAT scans with contrast are commonly done to image organs in the abdominal or pelvic regions.
The contrast dye works by blocking X-rays and highlighting the target region in white, according to Mayo Clinic. Oral contrast dyes are used to image the esophagus or stomach. Intravenous contrast dyes highlight blood vessels, the liver, the gall bladder or the urinary tract. Dyes are inserted rectally to highlight the intestines.
Mayo Clinic states that CAT scans with contrast are done with CT scanners. After the contrast dye is ingested or inserted, the patient lies on a narrow table that slides into the machine. The exterior part of the machine moves around the patient taking images of each layer of the body. The patient feels movement as the table moves though the machine and interacts with the technician via an intercom. Clicking and whirring noises are a normal part of the procedure. The patient needs to hold very still for high-quality images. At times, the technician may need the patient to hold his breath to produce a clearer image.