Some of the more common types of contrast material are iodine, barium, barium sulfate, and gastrografin. Contrast material is administered to the patient through one of four ways:
- Intravenous CT contrast: Highlights the blood vessels to increase the visibility of structures like the brain, spine, liver and kidney. The contrast agent is clear and water-like, usually containing iodine. Typically, the contrast enters the patient through a small needle inserted into a vein the arm or hand. The contrast then circulates the body through the bloodstream. It weakens the CT’s x-ray beam, so the blood vessels and organs that have absorbed the contrast will show up white on the CT image. After the CT scan, the kidneys and liver expel the contrast from the body.
- Oral CT contrast: Highlights the gastrointestinal organs in the abdomen and pelvis. The two most common types of oral contrast are barium sulfate and gastrografin. Patients drink the equivalent of three or four 12 oz drinks of contrast. The contrast travels to the gastrointestinal organs and, during the actual scan, weakens x-rays in that region, turning them to highlighted white areas on the CT image. Oral contrast requires the patient to fast for several hours before the CT scan.
- Rectal CT contrast: Highlights the large intestine and lower gastrointestinal organs. Like oral CT contrasts, rectal CT contrasts consist of either barium slufate or gastrografin. Rectal CT contrasts are administered by enema, and may cause some discomfort or fullness. Prior to the CT scan, the patient must fast for several hours, and cleanse the colon by enema the night before the scan. After the CT scan, the rectal CT contrast is drained, and the patient can go to the washroom.
- Inhalation: Used for highly specialized forms of brain or lung imaging available at only a few locations in the world. The patients inhales xenon gas to highlight the region being imaged.