No specific binding of [ 18 F]1c and [ 18 F]1f could be detected by PET imaging at any time after tracer injection in the rat brain. On the one hand, this may be due to the relatively low molar activity of the radioligands, as the tracers were produced in manual syntheses starting from 1 GBq of [ 18 F]fluoride; on the other hand, a higher free fraction of radioligands in the blood is desireable, to increase the initial brain uptake of PET ligand candidates.