Fibroblast activation protein inhibitor PET/computed tomography versus 18F-fluorodeoxyglucose PET/computed tomography in inflammatory bowel disease: a systematic review and exploratory meta-analysis with focus on ulcerative colitis

Fibroblast activation protein inhibitor (FAPI) PET/computed tomography (CT) is an emerging molecular-imaging approach for inflammatory bowel disease (IBD), particularly where fibroblast activation, stromal remodeling, and fibrosis are clinically relevant. Fluorodeoxyglucose (FDG) PET reflects inflammatory glucose metabolism but may be limited by physiologic bowel uptake and poor fibrosis specificity. To review original human studies evaluating FAPI-PET and FDG-PET in IBD, perform exploratory comparative synthesis where extractable data permitted, and appraise the ulcerative colitis-specific evidence base. Original human studies of FAPI-PET and FDG-PET in Crohn disease, ulcerative colitis, or mixed IBD cohorts were identified and categorized as direct comparative, supportive FAPI, or supportive FDG studies. Extractable 2 × 2 diagnostic data were summarized descriptively. Sensitivity analyses were performed by reference standard type and by excluding surgical or stricturing-enriched cohorts where feasible. Eleven original studies were included, of which four formed the direct comparative core. Three studies contributed segment-level 2 × 2 data to the primary lesion detection dataset, including Crohn disease and ulcerative colitis cohorts and different FAPI radiopharmaceuticals. In this exploratory segment-level aggregate, FAPI-PET showed descriptively higher sensitivity, specificity, accuracy, and diagnostic odds-ratio than FDG-PET. Restriction to endoscopy-referenced cohorts preserved the direction of effect. Patient-level 2 × 2 tables were not uniformly reported, so patient-level pooled estimates could not be generated. FAPI-PET is a promising imaging modality in IBD, with the strongest evidence in Crohn disease and fibrostenotic characterization. In ulcerative colitis, direct comparative evidence remains sparse.