RT Journal Article SR Electronic T1 Specific activity is not related to [11C]PiB retention in older adults JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 552 OP 552 VO 51 IS supplement 2 A1 Jitka Sojkova A1 Yun Zhou A1 Susan Resnick A1 Dean Wong YR 2010 UL http://jnm.snmjournals.org/content/51/supplement_2/552.abstract AB 552 Objectives Only with ultra high specific activity (SA) have studies with transgenic mice shown increased effective binding of [11C]PiB (Maeda et al J Neuroscience 2007;27:10957). In this study, we investigate the relationship between specific activity and [11C]PiB retention in human cross-sectional and longitudinal studies. Methods Sixty-five participants (7 with mild cognitive impairment (MCI)) in the Baltimore Longitudinal Study of Aging (mean age 78.1 (SD 6.6 years) underwent 89 [11C] PiB studies with mean 1.5±0.5) year follow-up between repeated studies. Fifteen regions of interest (ROIs) were drawn on coregistered MRI and applied to the DVR images. The DVR images were generated by using a simplified reference tissue model with linear regression and a spatial constraint algorithm (Zhou et al Neuroimage 2007;36:298). Mean cortical DVR (mcDVR) of 8 cortical regions was the outcome measure. Mass dose of [11C]PiB was obtained from time activity curves. SA was investigated in relation to age, diagnostic group, and tertiles of mcDVR; correlations were calculated between SA and mcDVR and the 15 regional DVRs. In 24 participants, differences in SA over time were evaluated relative to differences in cDVR (ΔcDVR). Results Mass dose of [11C]PiB was approximately 0.22 μCi/cc brain tissue. At baseline, mean SA was 5.7±3; range 1 -14.6) Ci/μmol and mcDVR was 1.18±0.26, range 0.89 - 1.81). SA in participants with MCI (mcDVR 1.38±0.33)) did not differ significantly from controls (mcDVR 1.16±0.24); p>0.05. SA was not correlated with cDVR (both mcDVR and DVR of 15 ROI’s) in the entire group and when evaluated by mcDVR and age tertiles (p>0.05). No nonlinear trends between SA and mcDVR were noted. Differences in SA at 1.5±0.5 year repeat compared to prior scan were not associated with ΔcDVR (p>0.05). Conclusions In older adults, [11C]PiB retention is independent of SA at mass/kg levels comparable to those used with transgenic mice showing effective binding of [11C]PiB. Research Support Supported in part by the Intramural Research Program, NIA, NIH and N01-AG-3-2124, and K24 DA000412(DFW)