Doctors are saving lives with virtual, 3D exams that are less invasive than a conventional optical colonoscopy.
MoSt PeoPle oVer old ignore their doctor’s advice and forgo the standard, invasive test that screens for
50 years
colorectal cancer and precancerous growths. Fortunately, a computer-based, noninvasive alternative to the conventional optical colonoscopy, known as virtual colonoscopy, is changing people’s attitudes—and could save tens of thousands of lives each year.
A virtual colonoscopy starts with computed tomography (CT), a common diagnostic technology that uses X-rays to record cross-sectional, 2D images of the body’s interior. A 3D model is constructed by segmenting the colon from the rest of the abdomen and using an electronic cleansing algorithm to factor out fecal material. Next, doctors use visualization software to navigate a virtual fly-through of the colon. If a polyp or
suspicious growth is found, doctors can perform a virtual biopsy and investigate further.
The case for a convenient mass-screening method is strong, says Arie Kaufman, chair of the computer science department at New York’s Stony Brook University. Colorectal cancer is the third most common cancer and the second leading cause of cancer deaths in the U.S., with more than 140,000 new cases and more than 50,000 deaths a year. “If all patients 50 years of age and older will participate in these screening programs, over 92% of colorectal cancer will be prevented and over 600,000 lives could be saved worldwide every year,” Kaufman says.
Virtual colonoscopies became possible in the mid-1990s, when Kaufman and others developed volume-rendering techniques that enabled 3D, virtual fly-throughs and associated tools, which were soon commercialized.
A screenshot of a user interface for virtual colonoscopy and computer-aided detection.
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Virtual colonoscopies have recently earned the imprimatur of the medical establishment, which prefers the formal term CT colonography. In a study at U.S. military hospitals, 1,233 symptomless subjects underwent a virtual colonoscopy, followed by a conventional optical colonoscopy, on the same day. The virtual colonoscopy results, reported in the New England Journal of Medicine in 2003, showed 94% sensitivity (real polyps found) and 96% specificity (false-positive rate) for polyps 8mm and larger— numbers comparable to those of optical colonoscopy, the gold standard among doctors. Subsequently, the U.S. Food and Drug Administration approved virtual colonoscopy for colon cancer screening.
Virtual colonoscopy outperforms optical colonoscopy in certain ways, advocates claim. A University of Wisconsin study, for example, found it better at finding 8mm and 10mm polyps. It also outperforms optical colonoscopy in finding polyps hidden in folds and around corners of the twisting tube of the colon, and in reliably reaching the farthest reaches, called the caecum. It can also do something optical colonoscopy, by its nature, cannot do: spot polyps on the colon’s outer walls.
Also, because it is noninvasive, a virtual colonoscopy avoids the risk of the rare but deadly tears or holes that can occur during an optical colonoscopy (and which can require immediate surgery). “The examination is done on the data, rather than the patient,” says Dr. C. Daniel Johnson, a principal investigator at the Mayo Clinic in Scottsdale, AZ, and the lead researcher on several studies.
Virtual colonoscopy’s only significant health risk is a patient’s exposure to radiation. This trade-off
screenshot courtesy of arie e. kaufman
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