Emerging PET radiotracers for vascular imaging.

Imaging plays an important role in the clinical management of patients with large-vessel vasculitis (LVV), both to confirm the diagnosis at the time of initial presentation and to identify disease relapses in individuals with established disease. The big advantage of PET imaging over other non-invasive imaging modalities is the ability to employ targeted radionuclide probes to localize and track cellular pathways, providing in vivo assessments of disease activity. While 18F-fluorodeoxyglucose (FDG) has good diagnostic accuracy for LVV, this tracer is taken up by all glucose metabolizing cells in the vessel wall and so non-specific arterial uptake that is often unrelated to inflammatory disease activity can occur in patients despite a good clinical response to treatment. Advances in PET imaging technology and methods such as delayed imaging protocols and quantitative parametric imaging have the potential to improve the diagnostic accuracy of 18F-FDG in LVV. However, there is nevertheless a real clinical need for new PET tracers that target specific immune cells and inflammatory processes to inform about underlying disease pathology and guide individualized treatments for LVV. Many emerging PET tracers developed initially for oncology or atherosclerosis imaging could provide useful measures of disease activity in LVV, including tracers targeted to receptors on monocytes/macrophages, T and B lymphocytes and other inflammatory cells implicated in the pathogenesis of the disease. This focused review will discuss several of the most promising emerging PET radionuclide tracers for imaging vascular inflammation.