Methods: Six stump-tailed macaques (age: 17.3±6.3; mean±s.d.) were scanned on 2 separate days (time between scans: 91±37 days) with [I]MNI308 (injected activity: 92.8±32.7 MBq). Serial, dynamic SPECT scans were acquired for 3 h immediately following injection of [I]MNI308. Volumes-of-interest (VOIs) were drawn on an average image from the first SPECT scan day, and VOIs included whole brain, cerebellum, brainstem, thalamus, and frontal, temporal, parietal and occipital cortex. Retest scans were co-registered to their respective initial scans. VOI placement and scan coregistrations were conducted using commercially available software. Histopathological evidence suggested that the cerebellumwas void of amyloid plaque in stump tails, and was suitable for use as a reference region. SUVrs were calculated as the ratio of uptake in target VOIs/uptake in cerebellum. For each VOI, the average ratio for all scans from 90 to 150 min post injectionwas calculated. This post-injection interval represents a period of secular equilibriumwith unchanging SUVr values. This mean SUVr from each scan (test and retest) for a given animal was calculated, and the quotient (difference/mean), expressed as a percent, were calculated for each VOI.