Combined [18F]-FDG PET-MRI in Diagnostics and Surveillance of Small Bowel Crohn's Disease

Diagnostics and follow up of small bowel CD can be difficult, large parts of small bowel can't be assessed by conventional endoscopy. MRE can detect transmural lesions, but sensitivity is limited with luminal disease. SBCE can detect even small lesions, but specificity is low. More accurate tools for diagnostics are hence needed. Our aim is to is to show that [18F]-FDG-PET-MRE can be used in diagnostics and disease activity monitoring of small bowel CD

Volunteer patients with clinically suspected small bowel CD (i.e. ileitis in colonoscopy, diarrhea, anemia and elevated fecal calprotectin or suspected CD in cross sectional imaging) are recruited from the outpatient clinic of gastroenterology in Turku University Hospital. The patients must fulfil the eligibility criteria and give their signed approvement prior to their enrolment into the study. All patients have previously been in ileocolonoscopy.

After screening, the patients have routine blood samples taken. A complete blood count (CBC), C-reactive protein (CRP), creatinine, alanine aminotransferase (ALAT), alkaline phosphatase (AFOS) and albumin will be analyzed from each patient's blood sample and fecal calprotectin analyzed from stool. Patients are then assessed with PET-MRE using 18-fluorodeoxyglucose ([18F]-FDG) tracer. The patients must fulfil the eligibility criteria and give their signed approvement prior to their enrolment into the study.

Patients fast for six hours prior to PET-MRE study. Oral mannitol is used as enteral contrast. Venous catheters will be placed at both antecubital veins for injection of [18F]-FDG and gadolinium contrast agent for MRE-sequences. Patients will lie prone for approximately 1.5h during the PET-MRE imaging. Prior to imaging, fasting glucose is measured from venous blood. During the imaging, FDG -activity will be measured from venous blood. The uptake of FDG in small bowel will be measured from the images obtained from segments with inflammation and healthy-looking segments for comparison.

If no strictures are present in the PET-MRE, the patients will go through SBCE to confirm the diagnosis of small bowel CD. The patients are arranged a visit to clinician in the outpatient clinic of gastroentereology in Turku University Hospital. The clinicians have access to MRE-data, endoscopy and SBCE-data and laboratory data, but are blinded from PET-results to avoid bias. The clinicians choose adequate treatment for each patient individually following general guidelines (such as ECCO) of treatment of small bowel CD. The patients diagnosed with small bowel CD will undergo a repeated PET-MRE following the same protocol as the first diagnostic PET-MRE to assess response to therapy. After the follow-up PET-MRE, patients medical history including laboratory and medication data will be followed and gathered for 12 months.

Primary outcome is to show that standardized uptake values (SUV) measured in [18F]-FDG-PET-MRE are higher in patients with CD than in patients not diagnosed with CD.

Secondary outcome is to show that starting effective medical therapy to small bowel CD decreases SUV in small bowel segments with CD inflammation. Secondary aim is also to investigate whether changes in SUV can predict long term disease outcomes.