MR colonography has yet to capture radiologists' imagination to the same extent as CT. But the radiation-free exam has a bright future, especially if stool tagging techniques can avoid the need for bowel cleansing, according to speakers from the U.S. and Greece at ECR on Friday.

Patients with incomplete endoscopy results and individuals requiring an assessment of inflammatory bowel disease can already benefit from MR colonography, said Dr. Thomas Lauenstein, an assistant professor of radiology at Emory University in Atlanta. The technique may also come to play a role in colorectal cancer screening if it can demonstrate sufficient accuracy and patient acceptance.

Published figures put the sensitivity of MR colonography at around 85% for polyps 5 to 10 mm in diameter and 100% for polyps greater than 10 mm. These studies were all based on cancer screening in a high-risk population, however, so results were likely influenced by radiologists' expectations of finding pathology, Lauenstein said.

Lauenstein and colleagues conducted a trial designed to reflect a more general screening population using 294 subjects over 50 years of age. MR colonoscopy showed a sensitivity of 74% for the 5 to 10-mm polyps and a specificity of 97% compared with optical colonoscopy.

"We are not perfect, but we are quite good," he said. "But we also have to get away from the idea that colonoscopy itself has a sensitivity of 100%. That's not true."

Patient feedback showed acceptance for MR colonography and endoscopy to be equal, which surprised researchers. The greatest dislikes were insertion of a rectal tube during MR colonography and the need for bowel cleansing with optical colonoscopy. These could both be avoided in future MR colonography protocols by switching the tube for a catheter and finding a robust, reliable method for fecal tagging, Lauenstein said.

Wider public awareness of risks posed by medical radiation exposure could drive the popularity of MR colonography, according to Lauenstein. He predicts that the relative positions of CT and MR colonography could be quite different in five years.

"The proportion of exams carried out by the two techniques may not have switched completely, but I think the impact of MR will be higher in the future than it is now," he said.

Speaking at the same session, Dr. Nikolaus Papanikolaou from the radiology department at the University of Crete showed how alternative sequence options and choice of contrast agent can influence the clarity of MR-based bowel exams. It will be advances in hardware, however, that will make the greatest impact on MR colonography's prospects, he said.

"Further technical improvements may increase the likely role of MR colonography in colon cancer screening," he said. "I believe that the combination of parallel acquisition techniques and imaging at 3T could be the future of MR colonography."