Virtual Colonscopy

A virtual colonoscopy is a new, non-invasive diagnostic test that allows the Johns Hopkins colorectal cancer heath care team, using X-rays and computer software, to view two- and three-dimensional images of the entire colon and rectum to detect polyps and/r colorectal cancer.

A virtual colonoscopy is performed on a patient with an empty bowel.  Laxatives and suppositories may be prescribed to accomplish this, as well as a diet of clear liquid for a certain time before the procedure.  Sedation is not usually required.  Antispasmodic agents and/or contrast agents may be administered intravenously before the CT (computerized tomography) or MRI (magnetic resonance imaging) scan takes place.

The scan is performed with the patient holding his of her breath for approximately 20 seconds while lying on his or her back, and again, while lying face down.  To inflate the colon, air is pumped through a small, thin tube inserted into the rectum.  A radiologist manipulates and interprets the images.

Patients report that a virtual colonoscopy is more comfortable than either a barium enema procedure or a conventional colonoscopy.  A patient can resume normal activities immediately following the virtual colonoscopy.  If an abnormality is discovered, a patient can have a conventional colonoscopy the same day.

CT view of colon.
What the radiologist sees: the colon is represented by empty space, the arrow denotes a polyp.
3D Imaging of Colon
A 3D rendition of the colon with an arrow denoting a polyp.

Research has shown that a virtual colonoscopy allows doctors to see polyps more clearly and in more detail than the images produced using a barium enema, and nearly as accurately as a conventional colonoscopy.  Polyps smaller than 10 millimeters in diameter, however, may not appear on images captured during a virtual colonoscopy.  Because neither tissue samples are taken nor polyps are removed during a virtual colonoscopy if an abnormality is found.

Clinical trials about the virtual colonoscopy are in progress to determine and enhance its effectives. 

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