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CT colonography

Woman over 50If you are 50 or older, or approaching that age, you are probably already aware that a colon screening is recommended every 7 to 10 years for that age group. The goal of a colon screening is to look for colonic polyps, which are growths in the inner lining of the large intestine that can potentially turn cancerous. When the growths are found in their early stages, they can be removed before cancer has had a chance to develop.

CT colonography is a minimally invasive procedure that offers a good alternative to traditional colonoscopy for many patients. The exam generally takes about 15 minutes, and no anesthesia is required.

How it works

A CT scanner is used to acquire images of the colon and then a sophisticated computer translates these into detailed three-dimensional pictures of the large intestine. These can be viewed as conventional CT images or as "virtual fly-throughs" of the large intestine, similar to how a traditional colonoscopy would look.

CT technology allows us to see the inside of the colon in the kind of detail otherwise found only in a traditional colonoscopy, in which a patient is sedated and an endoscope is snaked into the large intestine.

How to prepare

As with a traditional colonoscopy, a bowel preparation will be needed the night before a virtual colonoscopy. This will include taking laxatives to clear the colon, and drinking a barium solution that will help your doctor to see polyps more distinctly. You will also need to refrain from eating or drinking anything but small amounts of water beginning the night before the exam. Your doctor will discuss the preparation with you in further detail.

The CT colonography exam is performed on an outpatient basis, and you will be able to drive yourself home from the exam.

What to expect

You will wear a hospital gown during your exam. You will be asked to lie down on the CT examination table, usually flat on your back, but possibly on your side or stomach. The technologist will help position you, and pillows may be used to help you maintain the correct position throughout the brief exam.

A small, flexible tube will be passed two inches into your rectum. The tube is used to gently pump carbon dioxide into the colon to eliminate folds or wrinkles that could make it difficult to detect polyps during the exam. Carbon dioxide is quickly reabsorbed back into the body so feelings of bloating and pressure are markedly minimized.

Once the colon has been adequately distended, the scan will begin. The table will automatically begin to move through the opening in the scanner, and will continue to move as the actual CT scanning is performed. You will be asked to hold your breath for 15 seconds, then you will be repositioned on the table for a second trip through the scanner. After the second scan is complete, the tube will be removed, and you will be able to go home. No recovery time is needed after this procedure.

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