Emerging PET-radiotracers in cardiovascular, neuro-inflammation, lung and rheumatological diseases: a narrative review

Background: Imaging plays a crucial role in the clinical management of patients with inflammatory diseases, both for diagnosis and in evaluating treatment response. 2-deoxy-2-[18F]-fluoro-D-glucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) is a non-invasive imaging technique that is gaining prominence in the study of various infectious and inflammatory diseases. Advances in PET imaging technology, along with the development of new radiopharmaceuticals, have the potential to enhance the diagnostic accuracy of imaging in the evaluation of inflammation, allowing for the tracking of disease activity through mechanisms distinct from FDG. Methods: This narrative review aims to explore and discuss the emerging role of new PET/CT radiopharmaceuticals in the field of inflammation taking into account findings from recent studies in this setting. Results: Preliminary promising findings are available in the literature regarding the potential usefulness of new radiotracers for investigating inflammatory diseases, especially in cardiovascular, neurological, rheumatological and pulmonary fields. In cardiovascular inflammation, different radiopharmaceuticals showed promising roles according to the disease evaluated, but globally the findings are preliminary and heterogeneous. Concerning cardiac sarcoidosis, somatostatin Receptor Subtype 2 (SSTR2)-ligands, translocator protein (TSPO) radiotracers, and hypoxic radiotracers were investigated but until now so strong evidence were available. About vasculitis, SSTR2-ligands and CXCR4 radiotracers showen the most promising findings, especially in the evaluation of treatment response. Regarding atherosclerosis and mycoarditis, we have positive preclinical studies but lack of evidence from a clinical point of view. For neuroinflammation, the available findings on new PET radiotracers are still limited even if TSPO PET seems the most promising due to the ability to image microglial activation. Instead, about lung and rheumatological inflammatory diseases, fibroblast activation protein inhibitors (FAPI) appear to be the most promising radiopharmaceutical, even better than [18F]FDG, although further solid data are needed. Conclusions: Emerging PET radiotracers showed promising results in detecting inflammatory diseases in different anatomical sites, but more robust and comprehensive studies are required for their clinical use.