Combined [18F]-FDG PET-MR Imaging: A promising tool for diagnostics of small bowel Crohn's disease.

Introduction Diagnostics of small bowel Crohn's disease (CD) can be difficult. Combined positron emission tomography-magnetic resonance enterography (PET-MRE) can be used to evaluate intestinal metabolism, but clinical use has been limited due to accessibility, costs, absence of standardized methods and diagnostic thresholds. Our aim was to show that combined PET-MRE can be used to diagnose active small bowel CD. Methods We performed a fusion PET-MRE-scan with [18F]-FDG-tracer to 30 patients with suspected small bowel CD in colonoscopy. Standardized uptake values (SUV) were measured from small bowel. The diagnosis was confirmed with small bowel capsule endoscopy. Clinicians chose appropriate medication to each patient blinded from SUV-results. Endoscopic, laboratory and MRE-findings were investigated in relation to SUV. Results Fusion PET-MRE outperformed MRE in diagnostic accuracy. Patients diagnosed with CD (N=24) had higher SUV than patients not diagnosed with CD (N=6) (3.34 vs. 1.84, p=0.022). A diagnostic cut-off at SUV at 2.5. could be used (AUROC=0.81). A higher SUV predicts need for immunosuppressive medication (p=0.0026) and biologics (p=0.0005). SUV correlates positively with SES-CD-score (Simple Endoscopic Score for Crohn's Disease), fecal calprotectin and CRP and negatively with Hb and serum albumin. Conclusion In future, [18F]-FDG PET-MRE can be used in diagnostics of small bowel CD as a safe alternative for capsule endoscopy. High SUV can predict a more progressive disease course and need for more advanced therapies.