Purpose: As dual-phase amyloid-PET can evaluate amyloid (A) and neurodegeneration (N) with a single tracer injection, dual-phase tau-PET might be able to provide both tau (T) and N. Our study aims to assess the association of early-phase tau-PET scans and ¹⁸ F-fluorodeoxyglucose (FDG) PET and their comparability in discriminating Alzheimer's disease (AD) patients and differentiating neurodegenerative patterns.

Methods: 58 subjects evaluated at the Geneva Memory Center underwent dual-phase ¹⁸ F-Flortaucipir-PET with early-phase acquisition (eTAU) and ¹⁸ F-FDG-PET within 1 year. A subsample of 36 participants also underwent dual-phase amyloid-PET (eAMY). Standardized uptake value ratios (SUVRs) were calculated to assess the correlation of eTAU and their respective ¹⁸ F-FDG-PET and eAMY scans. Hypometabolism and hypoperfusion maps and their spatial overlap were also evaluated at the individual level visually and semiquantitatively. Receiver operating characteristic analyses were performed to compare the discriminative power of eTAU, FDG, and eAMY SUVR between A-/T- and A+/T + participants.

Results: Strong positive correlations were found between eTAU and FDG SUVRs (r = 0.84, p < 0.001) and eTAU and eAMY SUVRs (r > 0.87, p < 0.001). Clusters of significant hypoperfusion with good correspondence to hypometabolism topographies were found at the individual level, independently of the underlying neurodegenerative patterns. Both eTAU and FDG SUVRs significantly distinguished A+/T + from A-/T- individuals (AUC_eTAU =0.604, AUC_FDG =0.748) with FDG performing better than eTAU (p = 0.04). eAMY and eTAU SUVR showed comparable discriminative power.

Conclusion: Early-phase ¹⁸ F-Flortaucipir-PET can provide perfusion information closely related to brain regional glucose metabolism and perfusion measured by early-phase amyloid-PET, even if less accurate than FDG-PET as a biomarker for neurodegeneration.