FOLR2 and acute respiratory distress syndrome: Based on the correlation of 18F-AzaFol uptake in the diseased tissue with the numbers of activated, FRβ-positive macrophages [19], quantitative thresholds could be defined to stratify patients according to disease severity and outcome, including recovery time (in ARDS) and to identify patients likely to benefit from macrophage-oriented therapies [36,57].