ROSSLYN, Va., Sept. 9, 1996 -- Biomedical engineers are using virtual reality imaging to develop a colon cancer screening test that is more comfortable, convenient and less expensive than the standard exam, which many Americans avoid.
Colon cancer, the No. 2 cancer killer in America, can be prevented if the bumps that grow into tumors are spotted early and removed. These bumps, called polyps, grow on the walls of the lower gastrointestinal tract. If they reach the size of a blueberry, they should be taken out.
The standard screening test requires sedation and the insertion of a long tube, called an colonoscope, into the lower intestinal tract. A lens at the end of the scope enables a doctor to look for polyps. Afterward, the patient spends several hours in recovery.
The exam, called colonoscopy, is a potential life-saver. It is usually done after other routine tests, such as the fecal occult blood test, suggest the presence of polyps. The National Cancer Institute and the American Cancer Society recommend that everyone over age 50 be screened for colon cancer.
But even physicians avoid the colonoscopy. For example, when Indiana doctor Doug Rex offered a free colonoscopy to 17,000 health care professionals and their spouses, only 959 responded. Nearly one out of four had polyps, some of which required follow-up.
"What we need is a less invasive screening test, one that people will accept," said David Vining, M.D., assistant professor of radiology at the Bowman Gray School of Medicine. "If everyone were screened, it would have a major impact on the incidence of colon cancer in this country."
Vining has developed a method of using a spiral CT scan to build a three-dimensional image of the entire colon. The scan itself takes about 50 seconds. The patient lies on a table, which moves through a rotating X-ray beam. Minutes later, the patient can go home.
The X-ray data is processed into a computer image that is color-enhanced so the thicker the wall of the colon, the brighter the color. This makes polyps easy to see.
The virtual image of the colon can take the form of a movie, showing a trip through a long, twisting tunnel. Or it can be rendered as a tube split down the middle like an open hot dog bun. Either way, the brightly colored areas indicative of polyps stand out.
A second major advantage of the virtual exam is cost. A colonoscopy, in addition to requiring sedation and risking bowel perforation, costs from $900 to $1,500. The virtual exam using sprial CT might cost $450 to $650, Vining said. The virtual procedure may also reduce overall health care costs if more people are examined and more cancers prevented.
Because of the potential cost savings, the research is supported through the Cost-Reducing Health Care Technologies Program jointly operated by the National Science Foundation and The Whitaker Foundation.
A preliminary study in 30 patients showed the test to be as accurate as a colonoscopy. But the image processing takes too long for routine clinical use. Vining's group has been working to reduce the image processing time and to improve clarity. Results of this work were recently presented at a meeting of the American College of Colon and Rectal Surgeons.
This fall, Vining's group will screen 200 volunteers to assess improvements in the system and compare results with those of a colonoscopy.
Virtual reality medical imaging is being pursued by numerous academic laboratories and by more than a dozen companies, but clinical acceptance and general use of the procedure could still be years away.
One limiting factor has been the amount of computing power necessary to adapt the procedure to the clinic. Vining expects this issue to resolve itself within the next five years as more powerful and affordable computers become widely available.