What is virtual colonoscopy?

Virtual colonoscopy (VC), or CT colonography, is a method of screening the colon for precancerous polyps. Using a CAT (computed tomography, or CT) scanner and computer methods of reconstructing the images, the colon can be evaluated without a colonoscope and without sedation.

Virtual colonoscopy takes the information produced by a CT scanner and processes it to produce an image of the colon's inner surface. When the colon is properly cleansed and distended (expanded) with air or carbon dioxide, and when the CT information is processed, health care providers can look at the inner lining or surface to detect polyps.

Why do we need another test to detect precancerous colon polyps?

It is estimated that several million people in the United States alone have not been properly screened for colorectal polyps. The best method for screening is a regular colonoscopy. However, there are simply not enough endoscopists to screen such a large number of patients. Other methods, such as sigmoidoscopy, evaluate only a part of the colon. Tests to detect small amounts of blood in the stool can miss polyps and even cancers. The barium enema is not nearly as sensitive as a regular colonoscopy.

If a noninvasive test could be developed that could select those patients with a polyp, then fewer and more focused colonoscopies could be performed. The combination of newer, faster CT scanners with computer software that would produce images equivalent to an endoscope seems to be a logical step in the development of such a test.

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