# 68Ga-FAPI PET/CT for non-invasive characterization and activity assessment of ulcerative colitis and Crohn´s disease

## TL;DR

A new PET imaging technique using 68Ga-FAPI-46 helps assess activity in inflammatory bowel diseases like Crohn's and ulcerative colitis by tracking fibroblast activation.

## Contribution

68Ga-FAPI-46-PET shows potential for non-invasive IBD activity assessment through fibroblast activation patterns in both Crohn's and ulcerative colitis.

## Key findings

- FAPI-uptake was significantly higher in active IBD compared to inactive disease.
- 68Ga-FAPI-46-PET showed distinct uptake patterns in IBD lesions, with active disease showing intense FAPI positivity.
- The technique detected fibroblast activation in both Crohn's disease and ulcerative colitis.

## Abstract

Inflammatory Bowel Diseases (IBD) comprise ulcerative colitis (UC) and Crohn’s disease (CD). Management of IBD requires assessment of disease activity, severity, extent and complications. Here, we describe the signal behavior of both CD and UC in 68Gallium- fibroblast activation protein inhibitor-based radiopharmaceuticals-46-positron emission tomography (68Ga-FAPI-46-PET) and evaluate the potential of 68Ga-FAPI-46-PET for activity assessment in IBD.

This analysis includes data of 43 IBD patients and 43 control patients examined by 68Ga-FAPI-46-PET/computed tomography (CT). Disease activity of IBD patients was assessed by colonoscopy. FAPI-positive gastrointestinal tract (GIT)-findings and healthy appearing GI structures were contoured. Non-IBD related FAPI-positive GIT-findings were ruled out by interdisciplinary consensus. Static and dynamic PET-parameters of FAPI-positive IBD lesions and healthy appearing GI structures were extracted and PET signalling was analyzed with respect to IBD subtype and disease activity.

We examined 20 CD patients and 23 UC patients (29 with active, 14 with inactive disease). FAPI-uptake in most healthy appearing GI structures of IBD patients was significantly increased compared to controls. Of 80 FAPI-positive GIT-findings, 14 were ruled out as non-IBD related and 66 FAPI-positive IBD lesions were analyzed. We observed equally high lesional FAPI-uptake in CD and UC. All patients with active disease showed at least one intensively FAPI-positive IBD lesion, while only 4/14 patients with inactive disease showed any FAPI-positive IBD lesion. Lesional and patientwise FAPI-uptake was significantly higher in active than in inactive disease. FAPI-positive IBD lesions showed a characteristic kinetic behaviour with two types of uptake patterns – one showing a continuous increase and the other an early peak followed by a plateau.

68Ga-FAPI-46-PET/CT appears promising for assessing disease activity in terms of fibroblast activation in both CD and UC.

The online version contains supplementary material available at 10.1007/s00259-025-07686-1.