Contrast media, often referred to as dye, makes blood vessels, specific organs and tissue stand out on a CT image, says Imaginis. Contrast media affects the beam of a CT scanner by weakening the X-rays as they pass through organs and blood vessels infused with dye. This creates highlights on the resulting CT images.
Iodine, barium and a substance called gastrografin are common dyes used in CT scanning, according to Imaginis. Contrast media is administered orally, rectally or intravenously, and in rare cases, the dye is inhaled. Intravenous contrast is usually used for scans involving the spine, heart, kidneys and liver. Scans of the gastrointestinal system may involve both an intravenous injection and an oral contrast to maximize results. Oral dye is typically used when scanning the pelvis and abdomen, while rectal dye enhances images of the large intestine and other pelvic organs. Special brain and lung imaging is performed with an inhaled dye.
Injecting iodine into the bloodstream is not dangerous, and the liver and kidneys eliminate it after a scan, notes Imaginis. People with certain conditions such as asthma, kidney problems, diabetes and allergies may have a reaction or problems eliminating the iodine. Barium and gastrografin are used for rectal and oral imaging and may cause minor side effects such as constipation.