Combined Cut-Off Point Determination Of F-18-Av-1451 (T807) Imaging Biomarker For Tau Burden And 2018 Nia-Aa Definition Facilitate Reclassification Of Alzheimer'S Disease

254 Objectives: In 2018, the National Institute on Aging and Alzheimer’s Association (NIA-AA) updated the definition for Alzheimer’s disease (AD) to base on in vivo biomarkers of abnormal β-amyloid (Aβ) and pathologic tau deposits instead of clinical symptoms. We had previously reported a cut-off point for preclinical/clinical AD using 11C-PIB PET as a valid in vivo biomarker of Aβ plaque. We hereby, in this prospective study, evaluated the ability of 18F-AV-1451 (T807) PET, a selective tau tracer, to measure the global and regional tau burden in the brain and aimed to define a cut-off point for AD. Methods: During Feb to Nov 2018, 43 patients (M: 17, F: 26; mean age=66.4±8.5 y, range: 50-79 y) with decreased recent memory in 1-2 years, with/without cognitive impairment, but without language dysfunction, tremor or balancing problem, prior history of stoke or other neurodegenerative diseases, were recruited into this study. They all underwent 3-tracers PET/CT: 18FDG (biomarker for prediction of future cognitive decline), 11C-PIB and T807 within 1 week. 18FDG PET was assessed visually for temporal-parietal hypometabolism. Regional and global cortical to cerebellum SUV ratios (SUVRs) were calculated for both 11C-PIB and T807 PET (35 and 85 min post injection respectively). Global SUVR on 11C-PIB PET >= 1.3 was defined as abnormal in Aβ burden. Based on 11C-PIB and 18FDG PET findings, patients were classified as: (1) 11C-PIB+ and 18FDG+ as probable-AD, (2) 11C-PIB+ and 18FDG- as AD pathologic change, (3) 11C-PIB- and 18FDG- as non-AD. Results: According to 11C-PIB and 18FDG PET findings, 17 patients (mean age=70±6.3 y) were diagnosed as probable AD, 4 AD pathologic change (mean age=66±12.5 y) and 22 non-AD (mean age=63.7±8.6 y). Regional T807 SUVR of probable-AD patients exhibited significantly higher tau burden than non-AD patients in lateral temporal (1.45±0.29 vs 1.09±0.06), posterior cingulate (1.40±0.28 vs 1.11±0.08), medial temporal (1.38±0.17 vs 1.10±0.10), occipital (1.37±0.29 vs 1.07±0.06), precuneus (1.35±0.30 vs 1.03±0.06), superior parietal (1.28±0.31 vs 0.97±0.06) and frontal (1.22±0.21 vs 1.00±0.07) regions (all P