Colon Cancer Screening, The Easy Way

Radiology researchers devise a workaround for a nasty problem

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A new software program promises to make one of medicine's more grimace-inducing checkups significantly simpler. By devising a way to digitally clean up three-dimensional X-ray images of the colon, a group of researchers at the State University of New York at Stony Brook hope to encourage more patients to receive their recommended colon cancer screenings.

Colorectal cancer kills close to 700 000 people each year worldwide--a staggering number considering that most of these victims are done in by a tumor that ticks like a time bomb for as long as 15 years before erupting. This easily foiled killer creeps up on so many people because the gold standard in colorectal cancer detection, the colonoscopy, is tremendously unpopular. The prescreening regimen requires ingesting nothing but liquids for 24 hours, including a diarrhea-inducing concoction that forces a patient to stay near the bathroom for hours. Then there's the test itself: a camera attached to a fiber-optic cable is inserted into a patient's rear and snaked through the colon. This allows a doctor to visually inspect the walls of the gut for the presence of polyps that could turn cancerous.

For the past few years, the option of a virtual colonoscopy has offered patients a partial reprieve by doing away with the inserted camera. Instead, a computed tomography (CT) scan renders a 3-D image of the colon, enabling doctors to perform noninvasive virtual fly-throughs of patients' digestive tracts. But recipients have still had to deal with the discomforting effects of the prescreening potion and diet. Now these researchers hope their method--partial volume segmentation, described in an upcoming article in IEEE Transactions in Biomedical Engineering --will banish that as well.

Their algorithm, an improvement on a technique developed in 2002, analyzes the CT scans and discriminates between the pixels that represent colon walls and those showing fluids and fecal matter. This allows doctors to remove the unwanted bits from the image of the colon the way a tourist would use Photoshop to erase strangers from vacation photos.

”Prepless virtual colonoscopy, meaning no laxatives or diet modification, is the holy grail that doctors have been looking for,” says Andrew Milano, a clinical professor of gastroenterology who performs virtual colonoscopy at New York University but was not involved in the Stony Brook study. Research shows that only about half of people older than 50 in the United States get their recommended screening for colorectal cancer, primarily due to the invasive nature of the standard colonoscopy, Milano points out.

For electronic colon cleansing to work, each patient has to ingest three shot-glass-size servings of a barium solution that attaches to the stool, making it easily detectable by the CT scanner, and a shot of iodine to make the stool softer and more uniform. This uniformity is important, says Jerome Zhengrong Liang, a radiology professor at Stony Brook's medical school and a member of the team that developed the technique. The software separates the colon from everything else, based on the difference between its density and that of stool and fluid; these differences are indicated by variations in image intensity on the CT scan. Big variations in the stool's consistency might cause the software to mistake fecal matter for part of the colon wall.

Reliably setting the boundary of the colon wall, says Liang, was the team's greatest technical challenge. The software had to screen out artifacts introduced by the CT scan, in particular one known as the partial volume effect. This effect renders extra layers at the places where, say, air and stool meet. ”The scanner generates values at these points, which might suggest that there's tissue there,” says Liang. ”That might make you think, because of the shape [a lump where the rest of the colon wall is smooth], that you're looking at a polyp when you're not.”

But the new software does an even better job of seeing past the artifacts than technology Liang and his colleagues previously patented, reducing the number of false positives by 50 percent. In 2000 the group founded Viatronix, in Stony Brook, to develop an earlier version of prepless virtual colonoscopy. The university is now in talks with several large manufacturers of medical imagers about licensing the new version.

Photo: Zhengrong Liang

Inside Out

Radiologists in New York have invented a technology that screens for colon cancer without discomfort.

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