Longitudinal evaluation of surrogates of regional cerebral blood flow computed from dynamic amyloid PET imaging

Surrogates of neuronal activity, typically measured by regional cerebral blood flow (rCBF) or glucose metabolism, can be estimated from dynamic amyloid PET imaging. Using data for 149 participants (345 visits) from the Baltimore Longitudinal Study of Aging, we assessed whether the average of early amyloid frames (EA) and R₁ computed from dynamic ¹¹C-Pittsburgh compound B (PiB) PET can serve as surrogates of rCBF computed from ¹⁵O-H₂O-PET. R₁ had the highest longitudinal test-retest reliability. Interquartile range (IQR) of cross-sectional Pearson correlations with rCBF was 0.60-0.72 for EA and 0.63-0.72 for R₁. Correlations between rates of change were lower (IQR 0.22-0.50 for EA, 0.25-0.55 for R₁). Values in the Alzheimer's metabolic signature meta-ROI were negatively associated with age and exhibited longitudinal declines for each PET measure. In age-adjusted analyses, meta-ROI rCBF and R₁ were lower among amyloid+ individuals; EA and R₁ were lower among males. Regional PiB-based measures, in particular R₁, can be suitable surrogates of rCBF. Dynamic PiB-PET may obviate the need for a separate scan to measure neuronal activity, thereby reducing patient burden, radioactivity exposure, and cost.