68Ga-FAPI PET/CT for non-invasive characterization of ulcerative colitis and Crohn's disease

Introduction: Inflammatory Bowel Disease (IBD), represents a complex spectrum of chronic inflammatory conditions of the gastrointestinal tract (GIT) including ulcerative colitis (UC) and Crohn´s disease (CD). The management and monitoring of IBD often necessitate the use of various diagnostic modalities to assess disease activity, extent, and complications. Positron Emission Tomography (PET) imaging utilizing fibroblast activation protein inhibitor (FAPI) has emerged as a promising diagnostic tool in detecting activated fibroblasts. Given the role of fibroblast activation and tissue remodeling in the pathophysiology of IBD, we aimed to explore the potential of the application of FAPI-PET in the context of IBD.

Methods: PET/CT (1 h post injection) with ⁶⁸Gallium-labelled Fibroblast Activated Protein Inhibitors (⁶⁸Ga-FAPI-PET/CT) were applied in 11 consecutive patients with pathologically confirmed IBD and a gender- and age-matched control group of 11 patients without IBD. Volumes of interest (VOIs) of standardized healthy GIT structures and visually FAPI-avid GIT-lesions were delineated using a isocontour tool. Uptake parameters (SUVmax and SUVmean) were extracted and analyzed with regard to differences between IBD entities and IBD disease activity status of patients (based on coloscopy findings and clinical parameters).

Results: 5 patients had UC, 5 CD and 1 colitis indeterminata. CD patients showed a tendency towards increased uptake in the healthy appearing ileum compared to UC patients and controls. The uptake of the other physiological gastrointestinal structures did not show significant differences between IBD patients and the control group. Visually discernable FAPI-avid lesions of IBD patients showed overall high FAPI-uptake (SUVmax: 4.5 +/- 2.3, SUVmean: 2.3 +/- 1.0). Lesions of CD patients showed higher uptake (SUVmax 5.9 +/- 1.7; SUVmean 2,8 +/- 0,7) than those of UC patients (SUVmax 3.0 +/- 1.5; SUVmean 1.7 +/- 0.6). With respect to localization, ileum lesions showed markedly increased uptake in CD patients (SUVmax 5.6 +/- 3.4; SUVmean 3.2 +/- 1.8) compared to UC patients (SUVmax 2.0 +/- 0; SUVmean 1.2 +/- 0) and similarly colon lesions (CD: SUVmax 6.0 +/- 1.5; SUVmean 2.7 +/- 0.4; UC: SUVmax 3.0 +/- 1.5; SUVmean 1.7 +/- 0.7). Lesions of patients with active IBD showed higher uptake (SUVmax 5.0 +/- 3.3; SUVmean 2.6 +/- 1.6). than lesions of patients with clinically inactive disease (SUVmax 3.0 +/- 1.6; SUVmean 1.6 +/- 0.8).

Conclusions: While current evidence regarding the application of FAPI-PET in patients with IBD is limited to case reports on CD, our findings suggest its potential as a non-invasive imaging tool for assessing inflammatory activity in both UC and CD. Further research involving larger cohorts and standardized imaging protocols is warranted to validate the actual clinical value of FAPI-PET in IBD. If substantiated, FAPI-PET may offer a valuable adjunct to established imaging modalities, aiding in personalized management strategies and treatment monitoring for patients with IBD.

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