A study published in the New England Journal of Medicine shows that virtual colonoscopies are able to detect 90% of precancerous polyps larger than 10 millimetres, which makes the procedure as reliable as traditional colonoscopy for finding cancer. The so-called “virtual” colonoscopy, also known as CT colonography or CTC, is performed mainly outside the body and uses an X-ray computed tomography or CT scanner.

The study involved 2,600 adults over the age of 50 with no significant risk factors for colon cancer. They were tested at 15 medical centers. All patients received both a virtual and a traditional colonoscopy.

C. Daniel Johnson, MD, professor of radiology at the Mayo Clinic in Scottsdale, Ariz, who led the study, and colleagues found that the procedure detected 90% of precancerous polyps 10 millimetres or larger. CT colonography also detected 78% of polyps as small as 6 millimeters in diameter. The procedure failed to detect about one in ten of the largest lesions. Previous studies showed that standard colonoscopies also failed to spot about 5 percent to 10 percent of the lesions.

The National Cancer Institute and the American College of Radiology Imaging Network funded the research.

Colon cancer is the second leading cause of cancer deaths in the United States and the third most common type of cancer. Colorectal cancer claims about 56,000 lives every year. The American Cancer Society estimates almost 150,000 new cases of colorectal cancer for 2008 in the U.S. Screening for polyps is recommended at age 50, but people avoid standard procedures because they are unpleasant.