Head-to-head comparison of relative cerebral blood flow derived from dynamic [18F]florbetapir and [18F]flortaucipir PET in subjects with subjective cognitive decline

Background Dynamic PET imaging studies provide accurate estimates of specific binding, but also measure the relative tracer delivery (R-1), which is a proxy for relative cerebral blood flow (rCBF). Recently, studies suggested that R-1 obtained from different tracers could be used interchangeably and is irrespective of target tissue. However, the similarities or differences of R-1 obtained from different PET tracers still require validation. Therefore, the goal of the current study was to compare R-1 estimates, derived from dynamic [F-18]florbetapir (amyloid) and [F-18]flortaucipir (tau) PET, in the same subjects with subjective cognitive decline (SCD).Results Voxel-wise analysis presented a small cluster (1.6% of the whole brain) with higher R-1 values for [F-18]flortaucipir compared to [F-18]florbetapir in the A beta-negative group. These voxels were part of the hippocampus and the left middle occipital gyrus. In part of the thalamus, midbrain and cerebellum, voxels (2.5% of the whole brain) with higher R-1 values for [F-18]florbetapir were observed. In the A beta-positive group, a cluster (0.2% of the whole brain) of higher R-1 values was observed in part of the hippocampus, right parahippocampal gyrus and in the left sagittal stratum for [F-18]flortaucipir compared to [F-18]florbetapir. Furthermore, in part of the thalamus, left amygdala, midbrain and right parahippocampal gyrus voxels (0.4% of the whole brain) with higher R-1 values for [F-18]florbetapir were observed. Despite these differences, [F-18]florbetapir R-1 had high correspondence with [F-18]flortaucipir R-1 across all regions of interest (ROIs) and subjects (A beta-:r(2) = 0.79, slope = 0.85, ICC = 0.76; A beta+: r(2) = 0.87, slope = 0.93, ICC = 0.77).Conclusion [F-18]flortaucipir and [F-18]florbetapir showed similar R-1 estimates in cortical regions. This finding, put together with previous studies, indicates that R-1 could be considered a surrogate for relative cerebral blood flow (rCBF) in the cortex and may be used interchangeably, but with caution, regardless of the choice of these two tracers.

Automated summary

[F-18]florbetapir and [F-18]flortaucipir showed similar R-1 estimates in cortical regions. This finding, put together with previous studies, indicates that R-1 could be considered a surrogate for relative cerebral blood flow (rCBF) in the cortex and may be used interchangeably, but with caution, regardless of the choice of these two tracers.