There were no differences between groups in injected dose, bolus to infusion ratio, or time of scan (data not shown). Concentrations of [123I]5-IA activity in the blood (kBq/mL) were measured in order to correct for potential differences between groups in radiotracer metabolism or protein binding. There were significant differences in total parent (kBq/mL) between nonsmokers and 1 day abstinent smokers and in fP between nonsmokers and 2 week abstinent smokers (Table 2). There were no differences in total parent (kBq/mL) or fP between groups at other time points, or between groups at any time point in free parent (kBq/mL). There was also variability between smokers who participated in multiple scans in changes in β2*-nAChR availability over time with some abstinent smokers showing dramatic changes in β2*-nAChR availability (up to 48% change in the cortex) and others showing barely any difference, e.g., less than 5%, over time (individual data not shown).
