Blog post by Michael Dolinger, MD MBA
Crohn’s disease (CD) is a complex inflammatory bowel disease that requires accurate imaging techniques to assess disease activity and extent. For years, Magnetic Resonance Enterography (MRE) has been the go-to imaging modality. However, recent advancements have placed intestinal ultrasound (IUS) on the radar as a viable, non-invasive alternative. So, how does IUS stack up against MRE, particularly when it comes to detecting small bowel disease? The 2018 METRIC Trial, one of the largest comparative studies on this subject, provides some crucial insights into the strengths and weaknesses of both imaging techniques .
The METRIC Trial: Key Findings
The METRIC Trial was a multicenter study designed to directly compare the diagnostic accuracy of MRE and ultrasound in detecting small bowel and colonic Crohn’s disease. The trial included 284 patients, both newly diagnosed and those experiencing a relapse, across eight UK hospitals. It aimed to assess how well each imaging modality could identify the presence, extent, and activity of Crohn’s disease against a "construct reference standard," which included patient follow-ups over six months .
Sensitivity for Small Bowel Disease
When it comes to small bowel disease detection, both MRE and IUS showed high sensitivity:
- MRE demonstrated an overall sensitivity of 97% for detecting small bowel disease presence, making it the more sensitive of the two tests.
- Ultrasound wasn’t far behind, with a sensitivity of 92% .
However, the gap widened when assessing disease extent (i.e., identifying the correct segment of the bowel affected by Crohn's). MRE's sensitivity for disease extent was 80%, significantly higher than the 70% achieved by IUS.
Specificity: The Ability to Rule Out Disease
Specificity measures the test's ability to correctly identify patients without the disease. In terms of small bowel disease:
- MRE had a specificity of 95%, again outperforming ultrasound, which had a specificity of 81% .
This difference is clinically important, as it suggests that MRE is slightly more reliable in ruling out false positives for small bowel disease.
What About Colonic Disease?
When it came to detecting colonic Crohn's disease, IUS outperformed MRE in newly diagnosed patients:
- IUS showed a sensitivity of 67% for colonic disease, while MRE’s sensitivity lagged at 47% .
Active Disease Detection
Detecting whether the disease is active is crucial in the management of Crohn's. In this area, MRE and IUS were again similar:
- MRE had a sensitivity of 96% for identifying active small bowel disease, while IUS had a sensitivity of 90% .
However, both imaging modalities performed equally well in detecting active colonic disease, with no significant differences in their specificity .
The Bottom Line: Both Have a Role
Both MRE and IUS are highly accurate in diagnosing small bowel Crohn’s disease. While MRE consistently demonstrated higher sensitivity and specificity, particularly for detecting the extent of small bowel disease, ultrasound, , remains a valid alternative—especially for its convenience, lower cost, and lack of radiation.
For patients requiring frequent monitoring or those who cannot tolerate MRI, intestinal ultrasound is a very effective alternative, especially given its real-time imaging capabilities and patient-friendly profile.
Conclusion
For clinicians managing Crohn's disease, both MRE and ultrasound offer valuable insights, but the choice of modality should depend on the specific clinical context. While MRE holds a slight edge in diagnostic accuracy, ultrasound provides an excellent, non-invasive, repeatable option for many patients. The METRIC Trial underscores the importance of understanding the strengths and limitations of both tools, ensuring clinicians can provide the most accurate and personalized care possible.
