Quantitative characterization of brain β-amyloid in 718 normal subjects using a joint PiB/FDG PET image histogram.

We have previously described an automated system for the co-registration of PiB and FDG PET images with structural MRI and a neurological anatomy atlas to produce region-specific quantization of cortical activity and amyloid burden. We also reported a global joint PiB/FDG histogram-based measure (FDG-Associated PiB Uptake Ratio - FAPUR) that performed as well as regional PiB ratio in stratifying Alzheimer's disease (AD) and Lewy Body Dementia (LBD) patients from normal subjects in an autopsy-verified cohort of 31. In this paper we examine results of this analysis on a clinically-verified cohort of 718 normal volunteers. We found that the global FDG ratio correlated negatively with age (r(2) = 0.044) and global PiB ratio correlated positively with age (r(2)=0.038). FAPUR also correlated negatively with age (r(2)-.025), and in addition, we introduce a new metric - the Pearson's correlation coefficient (r(2)) of the joint PiB/FDG histogram which correlates positively (r(2)=0.014) with age. We then used these measurements to construct age-weighted Z-scores for all measurements made on the original autopsy cohort. We found similar stratification using Z-scores compared to raw values; however, the joint PiB/FDG r(2) Z-score showed the greatest stratification ability.