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

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 (SUV_Max) was measured in the small intestine and compared with MRE findings. The median SUV_Max 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.

Keywords: Crohn’s disease; Diagnostics; FDG; IBD; PET-MRI.

Fig. 1

Study design outline. Hemoglobin (Hb), C-reactive protein (CRP), serum albumin (Alb), fecal calprotectin (FC), Simple Endoscopic Score for Crohn’s Disease (SES-CD), inflammatory bowel disease (IBD), Simplified Magnetic Resonance Index of Activity (sMARIA), maximum standardized uptake value (SUV_Max), small bowel capsule endoscopy (SBCE)

Fig. 2

A 27-year-old female with small bowel CD related inflammation in terminal ileum (black arrows pointing at a distal skip lesion and white arrows pointing at a proximal skip lesion). In first diagnostic T2-weighted MRE inflammation is barely seen, sMARIA score (simplified Magnetic Resonance Index of Activity) 1 (A). In fused [¹⁸F]-FDG PET-MRE (B) inflammation is clearly seen in both segments, SUV_Max 6.6. Follow-up [¹⁸F]-FDG-PET-MRE was done 98 days after the diagnostic. No visible inflammation in T2-weighted MRE, sMARIA score 0 (C) and a clear decrease in inflammation is seen as [¹⁸F]-FDG-activity has subsided in fused [¹⁸F]-FDG PET-MRE, SUV_Max 1.3 (D)

Fig. 3

(A) Maximum standardized uptake value (SUV_Max) measured in the initial diagnostic [18 F]-FDG PET-MRE of the small intestine in patients diagnosed with small bowel Crohn’s disease (CD), compared to the 3-month follow-up imaging. A statistically significant decrease (p = 0.0025, Linear mixed model) was observed following the initiation of medical therapy. (B) The Simplified Magnetic Resonance Index of Activity (sMARIA) score, indicating CD activity in MRE, is shown for patients at diagnosis and at the 3-month follow-up. The median sMARIA score was significantly lower in the follow-up imaging (p = 0.001, Wilcoxon matched-pairs signed-rank test). (C) Fecal calprotectin (FC) levels at the time of the initial diagnostic [¹⁸F]-FDG PET-MRE and at the 3-month follow-up are shown. Median FC levels were significantly reduced at follow-up (p = 0.004, Linear mixed model), reflecting a biochemical response and decreased inflammation ** p ≤ 0.005