Structural T1-weighted MRI brain scans were acquired from all participants. Scanner and acquisition details at each site are provided in Table S1 in the online supplement. Data were prepared in FreeSurfer (version 5.3), a fully automated MRI processing pipeline that identifies seven bilateral subcortical and 34 bilateral cortical regions of interest (24, 25). A majority of the data sets were prepared using CBRAIN, a network of high-performance computing facilities in Canada (26). The volume of subcortical regions of interest and mean thickness of cortical regions of interest served as the dependent measure in all analyses. The use of FreeSurfer in multisite analyses has been validated in previous ENIGMA studies (27−30) that established a standardized protocol of quality control procedures performed at each site (http://enigma.ini.usc.edu/protocols/imaging-protocols/). This includes detection of outliers and visual inspection of all data in a series of standard planes (for more details, see the Supplemental Methods section in the online supplement). An additional level of visual inspection was performed centrally at the University of Vermont on a randomly selected subsample of participants to ensure uniformity of quality control across sites.
