Neuroimaging was performed on a 3T Siemens Tim Trio MR scanner (Siemens AG, Erlangen Germany) with a 12-channel head coil. A high-resolution, 3-dimensional, sagittal, magnetization-prepared rapid gradient echo scan (MPRAGE) T1 scan was acquired (repetition time [TR] = 2400ms, echo time (TE) = 3.16 ms, flip angle = 8°, inversion time = 1000 ms, voxel size = 1×1×1 mm3 voxels, 256×256×256 acquisition matrix, 162 slices).
Structural volumes were obtained using the FreeSurfer software suite (v5.1) (Martinos Center, Harvard University, Boston, MA, USA; http://surfer.nmr.mgh.harvard.edu). Briefly, this automated software program transforms MPRAGE images of an individual into a template space with the skull stripped and the brain segmented into white matter, gray matter, and ventricles. Cortical and subcortical image segmentation was completed using a surface deformation program [81 (link)–82 (link)]. Reviewers trained in FreeSurfer processing confirmed the quality of segmentation and volumes. Manual edits were performed only when outliers were identified. These manually-corrected scans were then reanalyzed. Regional brain volumes were normalized with respect to total intracranial volume (ICV) using a least square residual regression model across the entire cohort in order to account for possible variations in head size [36 (link), 83 (link)–86 (link)].