Evaluating ¹⁸F-Florzolotau tau PET for Alzheimer's disease diagnosis with ¹⁸F-Flortaucipir as reference

Tau protein aggregation is a hallmark of Alzheimer's disease (AD) pathology. Semi-quantitative analysis using regions of interest (ROIs)-based standardized uptake value ratios (SUVRs) serves as a major Tau positron emission tomography (PET) biomarker for AD diagnosis and staging. This study aims to evaluate the diagnostic performance of the second-generation tau tracer ¹⁸F-Florzolotau, including the impact of semi-quantitative reference region and ROIs methodology and partial volume error (PVE) correction. Data from the FDA-approved tracer ¹⁸F-Flortaucipir provide benchmark context, aiming to evaluate the performance.

A total of 842 participants from two cohorts underwent tau PET imaging with either ¹⁸F-Flortaucipir (n = 741) or ¹⁸F-Florzolotau (n = 101). The ¹⁸F-Flortaucipir cohort contains 384 normal controls, 292 patients with mild cognitive impairment, and 65 AD dementia. The ¹⁸F-Florzolotau cohort contains 27 normal controls, 26 patients with mild cognitive impairment and 48 AD dementia. SUVRs were calculated across four ROIs using six semi-quantitative methods varying by reference region and PVE-correction application. Diagnostic performance was assessed using the area under the curve (AUC) from receiver operating characteristic analysis. Partial correlations between SUVRs and clinical severity were evaluated.

¹⁸F-Florzolotau demonstrated high diagnostic accuracy (AUC: 0.96-0.98) for AD dementia and strong clinical correlations (|r|= 0.61-0.74). Performance varied with semi-quantitative methodology. The optimal approach used inferior cerebellar gray matter as the reference region, achieving the highest AUC and strong clinical correlations for ¹⁸F-Florzolotau. Results for ¹⁸F-Flortaucipir (AUC: 0.78-0.87; |r|= 0.29-0.45) provided consistent methodological insights supporting the choice of inferior cerebellar gray methodology.

¹⁸F-Florzolotau shows excellent diagnostic performance for AD dementia. The semi-quantitative methodology impacts results, with inferior cerebellar gray as the recommended reference region for optimizing ¹⁸F-Florzolotau SUVR analysis in AD dementia. These findings support the clinical utility of ¹⁸F-Florzolotau tau PET in AD.