The Role of FAPI PET/CT in the Assessment of Inflammatory Diseases.

PET/CT imaging with radiolabeled fibroblast activation protein inhibitors (FAPI), as an emerging modality for imaging fibroinflammatory diseases, targets activated fibroblasts involved in active tissue remodeling and fibrogenesis. Although initially introduced for oncologic indications, FAPI PET imaging provides a distinctive molecular insight into various fibroinflammatory conditions, including rheumatologic disorders, interstitial lung disease, inflammatory bowel disease, thyroid inflammation, and multiorgan immune‑mediated diseases. Unlike 18F-FDG PET/CT, which reveals the metabolic demand of inflammatory cells, FAPI PET imaging enables non-invasive distinction between active cellular inflammation and permanent fibrotic changes. Several studies demonstrate its exceptional diagnostic performance and the potential to monitor therapeutic response to anti-fibrotic and immunomodulatory medications. Despite these encouraging results, the transition of FAPI PET into routine clinical practice requires large-scale, multi-center prospective trials to standardize imaging protocols and establish validated diagnostic thresholds and interpretation criteria. Ultimately, FAPI imaging and theranostics have significant potential to revolutionize precision medicine for inflammatory and fibrotic disorders.