Alzheimer's Imaging Consortium.

Area of Science:

• Neuroimaging
• Nuclear Medicine
• Alzheimer's Disease Research

Background:

• Harmonizing tau positron emission tomography (PET) imaging across different tracers is crucial for accurate comparisons of tau burden in research and clinical settings.
• The universal tau PET scale (Uniτ) was developed to standardize measurements from various tau PET tracers.

Purpose of the Study:

• To evaluate the performance of the Uniτ scale in harmonizing tau PET images from Flortaucipir, MK6240, PI2620, and RO948.
• To assess Uniτ's ability to create a universal scale for comparing tau burden across different tracers and studies.

Main Methods:

• Assessed 485 individuals across the aging and Alzheimer's disease (AD) spectrum with head-to-head tau PET scans.
• Generated standardized uptake value ratios (SUVRs) using the inferior cerebellar gray matter as a reference.
• Estimated Uniτ parameters on a training set and applied the derived equation to harmonize 3D tau PET images.

Main Results:

• Uniτ successfully harmonized Flortaucipir, MK6240, PI2620, and RO948 tau PET data to a common scale, showing strong agreement.
• Uniτ tau positivity classifications closely matched original SUVR-based classifications.
• Harmonization of entire 3D tau PET images reduced visual variability and yielded results consistent with ROI-based analyses.

Conclusions:

• Tau PET tracers can be effectively harmonized to a common scale using the Uniτ method with a large head-to-head dataset.
• Uniτ enables harmonization of entire 3D tau PET images, eliminating the need for pre-established regions of interest (ROIs).
• The Uniτ scale is freely accessible and applicable for both ROI and 3D tau PET image harmonization.