Certain exams require a special dye, called contrast, to be delivered into the body before the test starts. Contrast helps certain areas show up better on the x-rays.

• Contrast can be given through a vein (IV) in your hand or forearm. If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.
• Let your doctor know if you have ever had a reaction to contrast. You may need to take medications before the test in order to safely receive this substance.
• Before receiving the contrast, tell your health care provider if you take the diabetes medication metformin (Glucophage) because you may need to take extra precautions.

If you weigh more than 300 pounds, find out if the CT machine has a weight limit. Too much weight can cause damage to the scanner's working parts.

You will be asked to remove jewelry and wear a hospital gown during the study.

Some people may have discomfort from lying on the hard table.

Contrast given through a vein (IV) may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.

An abdominal CT rapidly creates detailed pictures of the structures inside the belly area (abdomen).

This test may help detect or diagnose:

• The cause of abdominal pain or swelling
• Hernia
• The cause of a fever
• Masses and tumors, including cancer
• Infections or injury
• Kidney stones
• Appendicitis

The abdominal CT scan may reveal certain cancers, including:

• Breast cancer
• Cancer of the renal pelvis or ureter
• Colon cancer
• Hepatocellular carcinoma
• Lymphoma
• Melanoma
• Ovarian cancer
• Pancreatic cancer
• Pheochromocytoma
• Renal cell carcinoma (kidney cancer)
• Testicular cancer

The abdominal CT scan may show problems with the gallblader, liver, or pancreas, including:

• Acute cholecystitis
• Alcoholic liver disease
• Cholelithiasis
• Pancreatic abscess
• Pancreatic pseudocyst
• Pancreatitis
• Sclerosing cholangitis

The abdominal CT scan may reveal the following kidney problems:

• Acute bilateral obstructive uropathy
• Acute unilateral obstructive uropathy
• Chronic bilateral obstructive uropathy
• Chronic unilateral obstructive uropathy
• Complicated UTI (pyelonephritis)
• Kidney stones
• Kidney swelling (hydronephrosis)
• Kidney or ureter damage
• Polycystic kidney disease
• Uterocele

Abnormal results may also be due to:

• Abdominal aortic aneurysm
• Abscesses
• Appendicitis
• Bowel wall thickening
• Retroperitoneal fibrosis
• Renal artery stenosis
• Renal vein thrombosis

Risks of CT scans include:

• Being exposed to radiation
• Allergic reaction to contrast dye

CT scans do expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your doctor should weigh this risk against the benefits of getting a correct diagnosis for a medical problem.

Some people have allergies to contrast dye. Let your doctor know if you have ever had an allergic reaction to injected contrast dye.

• The most common type of contrast given into a vein contains iodine. If a person with an iodine allergy is given this type of contrast, nausea or vomiting,sneezing, itching,or hives may occur.
• If you absolutely must be given such contrast, your doctor may give you antihistamines (such as Benadryl) or steroids before the test.
• The kidneys help remove iodine out of the body. Those with kidney disease or diabetes may need to receive extra fluids after the test to help flush the iodine out of the body.

Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.

Shaw AS, Dixon AK. Multidetector computed tomography. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 4.