Abstract
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Objectives: Although the quantitative Standardized Uptake Value Ratios (SUVRs) for AV-1451 (aka flortaucipir) tau PET have been used so far in studying tauopathies, this technique requires sophisticated software processing which might not be available in future clinical workflows. We developed a visual scoring system for AV-1451 PET/MRI images, and compared these results to an established quantitative classification
Methods:
Methods: One hundred and seventy adults (20 with Clinical dementia Rating (CDR) above zero) underwent [18F]-AV-1451 positron emission tomography (PET). Seven were participants in Dominantly Inherited Alzheimer Network (DIAN). For quantitative analyses, as previously reported (Mishara et al., 2017) data were processed using region of interest (ROI) approach with FreeSurfer. Regional data were partial volume corrected and converted to SUVRs normalized to whole cerebellum. AV-1451 SUVR cut-off of 1.25 was used to define high tau. For visual assessment, PET and MRI images were fused using MIM (Cleveland, Ohio) and interpreted by two readers. Visual scoring scale was developed based on the degree of tracer uptake in regional and spatial distribution within frontal, parietal, temporal and occipital lobes (0: uptake similar, 1: mildly greater, 2: markedly greater than background). The off-target sites including basal ganglia, thalamus, midbrain, choroid plexus, and bone marrow were visually scored separately. Results: Visual assessment was generally concordant with quantitative approaches (93%). Visual/quantitative discordance was greater in few scans with high tau SUVRs. Nine participants (5%) had high tau on SUVRs while visual score was 0. Conversely, 4 participants (2%) have low tau on SUVRs while visual score has a range (1-2) in at least one region, excluding off-target sites. Conclusions: Visual/quantitative discordance can be secondary to AV-1451 tau uptake in adjacent off-target sites and may result in falsely high tau SUVR. Conversely, asymmetrically increased uptake in one region might result in falsely low tau SUVR. Combination of visual and quantitative tools for AV-1451 tau uptake might be necessary in clinical practice.
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