Immune-mediated inflammatory diseases (IMIDs) are characterized by chronic systemic inflammation and multi-organ involvement. Fibrosis formation in IMIDs can cause tissue destruction and subsequently organ malfunction. Fibroblast activation protein inhibitor positron emission tomography/computed tomography (FAPi PET/CT) represents a novel imaging technique that holds great potential to visualize in vivo fibrosis. We here provide an overview of available evidence on FAPi PET/CT imaging to visualize fibrosis in various IMIDs, including interstitial lung diseases, immunoglobulin G4-related diseases, cardiovascular diseases, kidney diseases, and gastrointestinal diseases. FAPi PET/CT imaging demonstrates high sensitivity in detecting early fibrosis, correlating with disease severity, across different IMIDs, showing superiority compared to conventional imaging modalities. Although FAPi PET/CT might be a useful tool to assess fibrosis formation, thereby aiding in grading disease severity and staging, future studies should include larger sample sizes in a broad variety of IMIDs with emphasis on the optimization of imaging protocols to further validate its diagnostic value.

Immune-mediated inflammatory diseases (IMIDs) are characterized by chronic systemic inflammation and multiorgan involvement. Fibrosis formation in IMIDs can cause tissue destruction and subsequently organ malfunction. Fibroblast activation protein inhibitor positron emission tomography/computed tomography (FAPi PET/CT) represents a novel imaging technique that holds great potential to visualize in vivo fibrosis. We here provide an overview of available evidence on FAPi PET/CT imaging to visualize fibrosis in var-ious IMIDs, including interstitial lung diseases, Immunoglobulin G4-related diseases, cardiovascular diseases, kidney diseases and gastrointestinal diseases. FAPi PET/CT imaging demonstrates high sensitivity in detecting early fibrosis, correlating with dis-ease severity, across different IMIDs, showing superiority compared to conventional imaging modalities. Although FAPi PET/CT might be a useful tool to assess fibrosis formation, thereby aiding in grading disease severity and staging, future studies should include larger sample sizes in a broad variety of IMIDs with emphasis on the optimiza-tion of imaging protocols to further validate its diagnostic value.