Time-activity curves (mean±SEM) for the 2 subjects undergoing full (8 hours) scanning with no smoking. The graphs demonstrate that 3 to 4 hours from the beginning of radioligand infusion are needed to reach a near steady state in the primary regions of interest for the bolus/infusion paradigm used herein. The average increase in radioactivity starting 3.5 hours after initiation of 2-[18F]fluoro-3-(2(S)-azetidinylmethoxy) pyridine (2-F-A-85380) administration was 3.2%, 3.2%, and 2.6% per hour for the thalamus, brainstem, and cerebellum, respectively.