Comparability of [ 18 F]THK5317 and [ 11 C]PIB blood flow proxy images with [ 18 F]FDG positron emission tomography in Alzheimer’s disease

For amyloid positron emission tomography tracers, the simplified reference tissue model derived ratio of influx rate in target relative to reference region (R 1 ) has been shown to serve as a marker of brain perfusion, and, due to the strong coupling between perfusion and metabolism, as a proxy for glucose metabolism. In the present study, 11 prodromal Alzheimer’s disease and nine Alzheimer’s disease dementia patients underwent [ 18 F]THK5317, carbon-11 Pittsburgh Compound-B ([ 11 C]PIB), and 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG) positron emission tomography to assess the possible use of early-phase [ 18 F]THK5317 and R 1 as proxies for brain perfusion, and thus, for glucose metabolism. Discriminative performance (prodromal vs Alzheimer's disease dementia) of [ 18 F]THK5317 (early-phase SUVr and R 1 ) was compared with that of [ 11 C]PIB (early-phase SUVr and R 1 ) and [ 18 F]FDG. Strong positive correlations were found between [ 18 F]THK5317 (early-phase, R 1 ) and [ 18 F]FDG, particularly in frontal and temporoparietal regions. Differences in correlations between early-phase and R 1 ([ 18 F]THK5317 and [ 11 C]PIB) and [ 18 F]FDG, were not statistically significant, nor were differences in area under the curve values in the discriminative analysis. Our findings suggest that early-phase [ 18 F]THK5317 and R 1 provide information on brain perfusion, closely related to glucose metabolism. As such, a single positron emission tomography study with [ 18 F]THK5317 may provide information about both tau pathology and brain perfusion in Alzheimer’s disease, with potential clinical applications.