EJNMMI Res. 2023 Oct 27;13(1):93. doi: 10.1186/s13550-023-01041-x.

ABSTRACT

BACKGROUND: Dynamic PET imaging studies provide accurate estimates of specific binding, but also measure the relative tracer delivery (R₁), which is a proxy for relative cerebral blood flow (rCBF). Recently, studies suggested that R₁ obtained from different tracers could be used interchangeably and is irrespective of target tissue. However, the similarities or differences of R₁ obtained from different PET tracers still require validation. Therefore, the goal of the current study was to compare R₁ estimates, derived from dynamic [¹⁸F]florbetapir (amyloid) and [¹⁸F]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 R₁ values for [¹⁸F]flortaucipir compared to [¹⁸F]florbetapir in the Aβ-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 R₁ values for [¹⁸F]florbetapir were observed. In the Aβ-positive group, a cluster (0.2% of the whole brain) of higher R₁ values was observed in part of the hippocampus, right parahippocampal gyrus and in the left sagittal stratum for [¹⁸F]flortaucipir compared to [¹⁸F]florbetapir. Furthermore, in part of the thalamus, left amygdala, midbrain and right parahippocampal gyrus voxels (0.4% of the whole brain) with higher R₁ values for [¹⁸F]florbetapir were observed. Despite these differences, [¹⁸F]florbetapir R₁ had high correspondence with [¹⁸F]flortaucipir R₁ across all regions of interest (ROIs) and subjects (Aβ-:r² = 0.79, slope = 0.85, ICC = 0.76; Aβ+: r² = 0.87, slope = 0.93, ICC = 0.77).

CONCLUSION: [¹⁸F]flortaucipir and [¹⁸F]florbetapir showed similar R₁ estimates in cortical regions. This finding, put together with previous studies, indicates that R₁ 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.

PMID:37889456 | DOI:10.1186/s13550-023-01041-x