EXETER, N.H. (AP) -- The radiologist peers into Pauline Morse's colon, pausing to inspect a fleshy fold before moving deeper into the shadowy twists and turns.

But Morse, 73, isn't lying on a table during this intimate tour of her insides - she's at home. The images were created with a virtual colonoscopy - a new procedure that relies on a computer scan instead of a scope to reveal cancer or suspicious growths.

Morse is among the early participants in the most comprehensive study yet to directly compare virtual or computer tomography colonoscopy to traditional colonoscopy, the gold standard for colorectal cancer screening. The comparison is important because the new procedure, though available at some hospitals, is considered experimental and not covered by most insurance.

During a colonoscopy, a doctor uses a flexible tube to view a sedated patient's entire colon and remove any suspicious growths that are discovered.

In a virtual colonoscopy, a CT scanner takes hundreds of X-rays of the colon. Sophisticated computer software combines the "slices" to produce two-dimensional images, which are analyzed later for growths. With a few clicks of a computer mouse, a radiologist can view the colon from every imaginable angle, zoom in on select areas and do a "fly-through" tour.

"You just lie on the bed, hold your breath, and they put you in the machine," Morse said.

Patients don't need sedation, and can return to work the same day as the procedure. But if the scan shows tumors or precancerous polyps, a traditional colonoscopy is needed to remove them.

"The big advantage is it's a quick test and it's noninvasive," said Dr. Geetanjali Akerkar, the study's principal investigator at Exeter Hospital. "If this test proves to be a very good test in terms of detecting polyps and cancer, then patients would be on a CT scan machine for five minutes, and if it's negative, they're pretty much finished."

Someone having the new procedure would be in and out of the hospital in less than half an hour, she said. A traditional colonoscopy lasts about 30 minutes, but because it involves sedation, patients typically spend about three hours in the doctor's office or hospital.

The study, funded by the National Cancer Institute, also is being conducted at Duke University, the University of Chicago and the University of California-San Francisco.

Though virtual colonoscopy is considered less invasive, Akerkar notes that it requires the same preparation as the other tests - drinking liquid the night before to cleanse the bowels - and an infusion of air into the colon during the procedure. That causes most of the discomfort, said Dr. David Weinberg, director of gastroenterology at Philadelphia's Fox Chase Cancer Center, which is not involved in the study.

"It's not the test. It's not the tube stuck in your rear end. It's the night before," he said.

Despite the "whiz-bang technology," virtual colonoscopy may not be better, Weinberg cautioned. But he said the study might produce other valuable insights - showing how to reduce the onerous test preparations, for example, or reducing the cost of testing.

Study participants also will undergo a third, less expensive procedure - a barium enema - that involves X-raying the colon after flushing it with a chemical solution. Other studies have shown barium enema to be far less effective than colonoscopy, and Akerkar said it was included in her study as a way to prove conclusively that it isn't reliable.

Sixty-three-year-old Hunter Farnham, who lives in Exeter, volunteered for the study because his mother died of colon cancer. All three tests were negative, he said.

Farnham found the traditional colonoscopy the easiest to endure.

"Barium enema was the least comfortable, virtual colonoscopy was in the middle, and colonoscopy was the most comfortable because I was knocked out," he said.

Morse, whose brother had colon cancer, signed up for the study after her doctor found blood in her stool. She rated the virtual colonoscopy the most comfortable, but said none of the tests was unbearable.

The tests revealed a small polyp that was removed and found to be benign, she said.

"I feel very assured that I don't have anything to worry about," she said.

Other studies have shown virtual colonoscopy to be 94 percent effective in finding polyps greater than 1 centimeter in size, which is comparable to traditional colonoscopy. But those involved only a few hundred patients, and researchers used different software packages to analyze the scans. The new study will include 4,000 patients, and all researchers are using the same equipment and software.

All participants will get a barium enema first and the virtual and traditional colonoscopies on the same day about a week later.

To avoid the chance that the results of one test could influence how researchers interpret the others, the doctors performing the traditional colonoscopy won't know the results of the other two tests until the very end of the procedure. Then, if the other two tests showed possible polyps, the doctor can go back and investigate.

If virtual colonoscopy proves to be an accurate screening tool, it will have the major drawback of not allowing suspicious growths to be removed on the spot, said Dr. Janice Rafferty, a colorectal cancer surgeon at the University of Cincinnati.

But she praised researchers for trying to find ways to encourage more people to get screened.

"If other procedures are a step in the right direction for people who won't have a colonoscopy, I say go for it," Rafferty said.

Cancers of the colon and rectum are the fourth most commonly diagnosed cancers and rank second for causing cancer deaths in the United States. The American Cancer Society recommends a colonoscopy every 10 years beginning at age 50 for people at average risk for the disease, but it estimates that less than half of those who should get screened do so.

"This search for a better way to do it is admirable, but the point is, get screened, don't wait for something better, just get it done," Rafferty said.

"You won't die of embarrassment, but you will die of colorectal cancer if you don't catch it."

Copyright 2002 The Associated Press. All rights reserved.