Intestinal stricture is a complication of Crohn's disease (CD), which is thought to be the result of chronic transmural inflammation combined with a dysregulated wound-healing process. While inflammatory strictures may respond to anti-inflammatory treatment, fibrotic strictures are usually anti-inflammation resistant, requiring further endoscopic balloon dilation or surgical intervention. Therefore, to determinate the inflammatory or fibrotic nature of intestinal stricture is a key step in the treatment of CD. 18F-FDG is a radiotracer reflecting the glucose metabolism of disease and is usually accumulated in inflammatory disease. 68Ga-FAPI is a novel radiotracer that specifically targets fibroblast activation protein (FAP). FAP is a membrane glycoprotein expressed on activated fibroblasts, which are key cells in the process of fibrotic intestinal stricture of CD. In this study, we hypothesis that the inflammatory or fibrotic nature of intestinal stricture can be non-invasively evaluated by 18F-FDG and 68Ga-FAPI PET/CT in patients with CD.

Patients with intestinal stricture will undergo 18F-FDG and 68Ga-FAPI PET/CT on two consectutive days. The accumulation of 18F-FDG and 68Ga-FAPI at the site of stricture will be determined by standard uptake value (SUV), molecular volume (MV), and total molecular index (TMI). In patients with a planned surgical resection of one or more stricture (s), the image results will be compared with histological findings.

Inclusion Criteria:

• Written informed consent signed
• Crohn's disease patients with proofs of intestine stricture by other modalities, e.g. MRI, CT, ultrasound, and/or endoscopy.

Exclusion Criteria:

• Known hypersensitivity to any of the excipients of 18F-FDG and 68Ga-FAPI.
• If the patients are on metformin, discontinuation of 48 hours is required before 18F-FDG injection to minimize the bowel uptake.
• Pregnant or breast-feeding women.
• Any mental condition rendering the patient unable to understand the nature, scope, and possible consequences of the study, and/or evidence of an uncooperative attitude.