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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Two types of scan, MRI and ultrasound, work well when used for staging and monitoring Crohn’s disease. MRI is more accurate.

Researchers compared a form of magnetic resonance (MR) imaging that includes an oral contrast agent, with ultrasound scans. They aimed to see which was better able to detect the presence and extent of active disease in the small bowel. The trial, carried out in eight NHS hospitals, involved 284 participants who had both MR and ultrasonography. While both tests performed well, MR was 10% more accurate for correctly classifying small bowel disease.

Patients were more likely to rate ultrasonography as acceptable or fairly acceptable. The tests were similar in terms of value for money. Clinicians were helped equally by the two tests in making potential treatment decisions.

The study suggests either MRI or ultrasound scans are acceptable tests to use for the management of Crohn’s disease.

Why was this study needed?

Management of Crohn’s disease depends on the extent and severity of active disease.

While ileocolonoscopy is the gold standard diagnostic test, it can only see a short way into the small bowel, so is less useful for assessing the extent of small bowel disease. It is also invasive and uncomfortable for patients. Both ultrasound and magnetic resonance imaging have been used to assess the small bowel at the start of the disease and when a flare-up is suspected.

Magnetic resonance (MR) enteroscopy is a newer technique that uses conventional MR scanners after the patient has been given an oral ‘biphasic’ contrast agent that distends the bowel and allows better assessment of mucosal folds and wall thickness.

While ultrasound scanners are more widely available, their accuracy may be more dependent on operator performance.

There have been questions about the quality of the previous research into the accuracy of these techniques and so this multi-centre study was designed to compare the performance of the tests in a prospective cohort design, primarily of patients with small bowel disease.

What did this study do?

The METRIC cohort study analysed a final cohort of 284 participants, 133 of whom were newly diagnosed with Crohn’s and 151 who were suspected of having relapses. 82% had small bowel disease and 45% had colonic disease. Participants in the original sample of 335 who were found not to have Crohn’s disease were excluded from the analysis.

Participants underwent both ultrasonography and MR enteroscopy, along with any other clinically-indicated investigations. For the reference standard, against which the scans were compared, a panel of clinicians reviewed all data about the participants, including their clinical course over six months. They recorded their opinion about the presence and activity of disease.

What did it find?

  • MR enteroscopy had a sensitivity of 80% for extent of small bowel disease (95% confidence interval [CI] 72% to 86%), while ultrasonography had a sensitivity of 70% (95% CI 62% to 78%). Specificity was 95% for MR enteroscopy (95% CI 85% to 98%) and 81% for ultrasonography (95% CI 64% to 91%).
  • For detecting the presence of small bowel disease, MR enteroscopy had a sensitivity of 96% (95% CI 86% to 99%) and ultrasonography had a sensitivity of 84% (95% CI 65% to 94%).
  • For colonic Crohn’s disease presence or extent, there was no overall significant difference in sensitivity or specificity between the tests.
  • Both imaging techniques were acceptable to patients as 99% of participants said they tolerated ultrasonography ‘well or fairly well’ as did 88% for MR enteroscopy.

What does current guidance say on this issue?

NICE published a guideline on the management of Crohn’s disease in May 2019. However, this guideline does not include information or advice on the use of MR enteroscopy or ultrasonography for monitoring disease.

What are the implications?

This study suggests that clinicians can use either MR or ultrasound to assess and monitor the progress of Crohn’s disease, as an adjunct to diagnostic ileocolonoscopy.

While MR is more sensitive, both tests perform well and ultrasound may be more acceptable to patients.

Citation and Funding

Taylor SA, Mallett S, Bhatnagar G et al. Magnetic resonance enterography compared with ultrasonography in newly diagnosed and relapsing Crohn's disease patients: the METRIC diagnostic accuracy study. Health Technol Assess. 2019;23(42).

This project was funded by the NIHR Health Technology Assessment Programme (project number 11/23/01).



NICE. Crohn’s disease: management. NG129. London: National Institute for Health and Care Excellence; 2019.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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