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Virtual colonoscopy - joyous reality!

Each year, approximately 55,000 Americans die of colon cancer, second only to lung cancer as a killer of both men and women. Screening for the disease is thus a key element in routine health examinations. Testing for hidden blood in the stool (e.g., Hemoccult) is the basic and simplest of the screening procedures, which should be done annually. Next is sigmoidoscopy, recommended every three to five years for persons after age 50.

Sigmoidoscopy involves the insertion of a rigid or, preferably, flexible tube about 18 inches in length through the rectum, through which the lower one third of the colon can be visually examined for polyps and other abnormalities. Although most abnormalities of the colon may be found in its lower third, periodic examination of the remaining two thirds is recommended, particularly when the sigmoidoscope reveals something.

In the past, x-ray examination of the entire colon, using a contrast medium such as barium, was the standard procedure. Any abnormalities in the normally smooth wall, such as cavities (from an ulcer or diverticulum) or protrusions (such as a polyp or tumor), would be seen in the x-ray--but only as two-dimensional shadows--as the barium worked its way through the colon.

With the arrival of fiber optics, it became possible to look directly at the inside of the colon--first through a short, flexible tube (the flexible sigmoidoscope) and later, through a much longer version of the same instrument, the colono-scope, which extends four to six feet into the colon. As might be expected, the invasion of one's colon by a six-foot mechanical "snake" is not the most pleasant of diagnostic procedures. Not only is it uncomfortable, it is time--consuming up to an hour or more) and expensive ($900 to $1,800 in many hospitals).

"Virtual reality" has become the rage in the entertainment world--and now we have "virtual colonoscopy," a way of viewing the inside of the colon without putting anything into it except air to inflate it. Developed by Dr. David Vining of Wake Forest University in North Carolina, the procedure uses computerized x-ray technology, enabling the examiner to obtain 3-D views of every square inch of the colon on a computer screen.

Dr. Vining's technique uses a new form of computer-assisted tomography (CT) scanning, called spiral CT. Ordinary CT scanners slowly take cross-sectional images of the body, one picture at a time. Spiral CT uses a machine that spins rapidly around the patient, taking 400 to 500 pictures in just 30 seconds.

Commercially available software programs then turn the spiral CT data into three-dimensional images on the computer screen. Using a joy stick," the doctor can move from place to place in the colon.

As with regular colonoscopy, the colon is flushed out with laxatives and enemas by the patient before coming to the examination. Instead of an hour or more under heavy sedation or even general anesthesia, however, the patient is off the table after half a minute of examination. Finally, after a long and welcome "evacuation of air in the colon," the patient is then on his or her way home. Should a polyp or other abnormality be found that requires biopsy or removal, however, colonoscopy is then required to get at it.

No, it's probably not at your local hospital yet. However, a number of research groups around the country are currently making use of it.
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Author:Brown, Edwin W.
Publication:Medical Update
Date:May 1, 1995
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