MRI-based Total Gray Matter Volume Estimation

Among adults, we obtained 842 T1-weighted magnetic resonance imaging (MRI) scans with two 3T General Electric platforms: 411 scans were obtained using a GE 3T Signa HDxt scanner with an eight-channel head, and 431 scans using a GE 3T Discovery 750 scanner with a 32-channel head coil. Among adolescents, 85 T1-weighted MRI scans were obtained using the same scanners: 49 scans were acquired using the GE Signa HDxt system and 36 scans were acquired using the GE Discovery 750 system. The acquisition sequences used are described in online Supplementary material.
In order to obtain the TGMV, all MRI scans were processed using FreeSurfer v6.0 (Fischl, 2012 (link)). TGMV was calculated as the sum of the cerebral cortical volume, the subcortical grey matter and the cerebellum grey matter (https://surfer.nmr.mgh.harvard.edu/fswiki/MorphometryStats). Quality inspection and editing was performed by trained research assistants following standard FreeSurfer procedures (McCarthy et al., 2015 (link)).