Images were reconstructed and analyzed as previously described including a nonuniform attenuation correction 43 with one exception. Specifically, in subjects who had more than one SPECT scan, the second and subsequent SPECT scans were coregistered to the same position as the first scan in order to apply the same region of interest template for that subject. MRIs were coregistered to the SPECT images to provide an anatomical guide for placement of the regions of interest using Medx (version 3.4) software (Medical Numerics, Inc., MD). Regions of interest chosen were those known to contain β2-nAChRs and included frontal, parietal, anterior cingulate, temporal and occipital cortices, thalamus, striatum (an average of caudate and putamen) and cerebellum. Regions-of-interest are corrected to account for differences in size. Two raters conducted the analysis. Variability between raters was <12 % across regions-of-interest. The mean of the analysis from the two raters is reported.
