Head‐to‐head comparison of Relative Cerebral Blood Flow derived from [18F]florbetapir and [18F]flortaucipir in subjects with Subjective Cognitive Decline

Abstract

AbstractBackgroundSeveral studies validated R1 as a marker for relative cerebral blood flow (rCBF). However, the similarities or differences of R1 estimates obtained from different PET tracers has never been investigated.AimThe aim of the current study was head‐to‐head comparison of R1 estimates, derived from dynamic [18F]florbetapir and [18F]flortaucipir PET scans.MethodFifty subjects with subjective cognitive decline (Aβ‐;N = 31, Aβ+;N = 19) underwent both [18F]florbetapir and [18F]flortaucipir PET (interval: 50.6 ± 34.7 days). Receptor parametric mapping (RPM) was used to generate R1 maps with cerebellar grey matter as reference. For voxel‐wise analyses, Statistical Parametric Mapping software (SPM12) was used. Furthermore, different regions‐of‐interest were assessed (in subject‐space). Paired t‐tests, coefficients of determination (r2) and ICC were used to compare R1 estimates from [18F]florbetapir and [18F]flortaucipir PET.ResultsVoxel‐wise analysis revealed only a few small significant clusters in part of the thalamus, insular gyri, midbrain and part of the cerebellum with higher R1 estimates for [18F]florbetapir and higher R1 estimates in the hippocampus, vermis, midbrain and calcarine sulcus for [18F]flortaucipir in Aβ‐ subjects (Figure 1a & 1b). In Aβ+ subjects, [18F]florbetapir showed higher R1 estimates only in part of the thalamus and [18F]flortaucipir showed higher R1 estimates in the hippocampus and striatum (Figure 1c & 1d). Despite the small amount of significant voxels, [18F]florbetapir R1 showed good correlation and excellent ICC with [18F]flortaucipir for whole brain (Aβ‐:r2 = 0.76, ICC:0.92; Aβ+:r2 = 0.60,ICC = 0.87).ConclusionTo conclude, [18F]flortaucipir and [18F]florbetapir showed similar R1 estimates in cortical regions, illustrating that R1 is a robust marker for flow independent of tracer of interest.