MRI was performed in a 3T Philips scanner equipped with a 32-channel head coil (Elition 3.0T X, Philips Medical Systems, Best, The Netherlands) at the Gruss Magnetic Resonance Research Center of Albert Einstein College of Medicine. High resolution 3D T1-weighted (MPRAGE) structural images of the brain were acquired for registration, and gray and white matter segmentation including segmentation of subcortical nuclei (TE/TR/TI= 4.6/9.7/900 ms, voxel size 1 mm isotropic, flip angle = 8°).
High-resolution T1-weighted structural images were brain extracted using the FSL FMRIB Structural Toolkit (14 (link)) and segmented into gray, white, and cerebrospinal fluid (CSF) components using FSL’s FAST (15 (link)). The Harvard-Oxford subcortical (16 (link)) atlas from the FreeSurfer software package (http://surfer.nmr.mgh.harvard.edu/) was used to perform automatic segmentation to extract subcortical volumes from all study participants including the caudate nuclei (regions 5 and 16 for the left and right caudate, respectively). These atlas regions were registered across our entire sample and volumes were extracted for each participant.