# Combined [18F]-FDG PET-MR imaging for monitoring small bowel crohn’s disease

## TL;DR

This study shows that combined PET-MR imaging can help track treatment response in small bowel Crohn’s disease by measuring changes in inflammation markers.

## Contribution

The study is the first to establish the use of PET-MRE for monitoring treatment response in small bowel Crohn’s disease.

## Key findings

- The median SUVMax decreased significantly from baseline to follow-up, indicating reduced inflammation.
- The sMARIA score and fecal calprotectin levels also declined significantly, supporting treatment efficacy.
- PET-MRE appears to be a useful tool for assessing biochemical response to treatment in newly diagnosed small bowel CD.

## Abstract

Crohn’s disease (CD) is a chronic and relapsing inflammatory disease of the gastrointestinal tract. Diagnostics and follow-up are difficult in small bowel, that can be only partially evaluated by conventional endoscopy. Combined positron emission tomography magnetic resonance enterography (PET-MRE) has shown potential in diagnosing small bowel CD, but its role in monitoring treatment response has not been previously established. This study aimed to evaluate whether PET-MRE can be used to assess the efficacy of medical therapy. We hypothesized that standardized uptake values (SUV) in inflamed small bowel segments would decrease following initiation of standard therapy. A total of 35 volunteer patients with clinically suspected small bowel CD were recruited. All patients underwent ileocolonoscopy and laboratory testing, followed by [18F]-FDG PET-MRE. CD diagnosis was confirmed by small bowel capsule endoscopy. Clinicians initiated treatment based on standard diagnostics, blinded to the PET results. Eighteen patients completed follow-up [18F]-FDG PET-MRE at three months. Maximum SUV (SUVMax) was measured in the small intestine and compared with MRE findings. The median SUVMax decreased significantly from baseline to follow-up (3.2 vs. 2.1, p = 0.0025). The Simplified Magnetic Resonance Index of Activity (sMARIA) was also significantly lower at follow-up (p = 0.001). Representatively, median fecal calprotectin declined (451 µg/g vs. 163 µg/g, p = 0.004). This preliminary prospective study suggests that [18F]-FDG PET-MRE may be a useful tool for assessing biochemical response to treatment in newly diagnosed small bowel CD.

Trial registration number: NCT06796959 (ClinicalTrials.gov). Retrospectively registered on 21.1.2025. Enrollment of first participant on 1.8.2020.

The online version contains supplementary material available at 10.1007/s00259-025-07524-4.