Magnetic resonance enterography compared with ultrasonography in newly diagnosed and relapsing Crohn's disease patients: the METRIC diagnostic accuracy study.

Crohn's disease is a waxing and waning lifelong inflammatory condition that affects the colon (large bowel) and small bowel. Treatment relies on accurately determining disease extent and underlying inflammation. Colonoscopy is very good for examining the colon, but it is invasive and, at best, can only visualise a few centimetres of the small bowel, so radiological imaging is very important. Magnetic resonance enterography (a type of magnetic resonance imaging scan) and ultrasonography are both radiological tests commonly performed in the NHS, and it is unclear which method is better. We performed a study to compare the accuracy of magnetic resonance enterography and ultrasonography for determining the extent of Crohn's disease in the bowel of participants newly diagnosed and in those participants with established Crohn's disease but with suspected deterioration. We also investigated how often radiologists agree with each other during test interpretation, the participant experience of undergoing the tests and their cost-effectiveness. We compared the tests in 284 participants (133 newly diagnosed and 151 with suspected deterioration). We found that both tests were accurate for detecting the presence (97% for magnetic resonance enterography and 92% for ultrasonography) and location (80% for magnetic resonance enterography and 70% for ultrasonography) of disease in the small bowel, but magnetic resonance enterography was better than ultrasonography for both (correctly classifying disease extent in 107 more participants for every 1000 participants with Crohn's disease). Magnetic resonance enterography was similarly better than ultrasonography at determining if the bowel was inflamed. The results were similar in newly diagnosed participants and those participants with suspected deterioration. Agreement between radiologists interpreting the same images was, at best, moderate for both tests. A total of 88% of participants tolerated magnetic resonance enterography well or fairly well, which was less than the percentage (99%) of participants who tolerated ultrasonography well or fairly well. Both tests had a similar effect on the treatment decisions made by doctors. Both tests were also similar in their value for money for the NHS.