Associations between pet tau and mri gray matter density and diffusion

We have recently investigated multiple MRI and PET imaging biomarkers for differentiating early Alzheimer's disease and mild cognitive impairment (MCI) patients from normal controls. Due to the relatively new development of the tau tracer, In vivo associations between intracellular tau tangles and MRI metrics have not been studied extensively in human subjects yet. 51 individuals (mean ± std of age: 75.4±7.6 years; 18 women) with [18-F] AV-1451 PET ligand for imaging hyper-phosphorylated tau, multi parametric MRI imaging metrics including diffusion and 3D structural T1 data were downloaded from ADNI website (www.adni.loni.usc.edu). Voxel based morphometry (VBM) was implemented to the structural MRI data to detect regional concentration of gray matter atrophy sing FMRIB Software Library (FSL, http://www.fmrib.ox.ac.uk/fsl) toolbox. Voxel-wise tract-based spatial statistics (TBSS) in FSL was used to analyze DTI fractional anisotropy (FA) data. 3D correlation test of each voxel across subjects was performed using the Analysis of Functional NeuroImages (AFNI, http://afni.nimh.nih.gov/afni) to derive the correlation coefficient Rho for each voxel between PET and MRI metrics. Higher tau deposition pattern in the temporal cortex and default mode network was identified as one primary component from concatenated tau images based on non-negative matrix factorization algorithm (Figure 1a). Based on ROI analysis, strong associations (r ≤-0.89, P≤0.008) were found between middle temporal tau depositions and FA value of the hippocampal portion of the cingulum bundle in MCI patients; and between middle frontal tau deposition and FA of the genu of corpus callosum (r = -0.9994, P<0.0001). Significant voxel-wise negative correlation between tau and GM density were found in the entorhinal and hippocampal regions, medial and orbito-frontal as well as cerebellum; with few positive correlations found in scattered brain regions including superior frontal cortex (corrected P<0.05, Figure 2). Significant voxel-wise negative correlations between tau and DTI FA were found in the hippocampal portion of the cingulum bundle (P<0.05, Figure 1b), thalamic radiation, inferior longitudinal fasciculus (corrected P<0.05) together with some positive correlations identified in frontal white matter (Figure 3).