Detailed Head Model Segmentation

The head models of the participants were represented by a grid of cubical voxels with a resolution of 0.40 mm using T1- and T2-weighted images. The models were segmented into 14 tissues/body fluids (i.e., the skin, fat, muscle, outer skull, inner skull, gray matter, white matter, cerebellar gray matter, cerebellar white matter, brainstem, nuclei, ventricles, cerebrospinal fluid, and eyes). To reconstruct the surfaces of the gray and white matter, brain tissues were segmented using FreeSurfer image analysis software from T1-weighted images [29 (link),30 (link)]. Non-brain tissues were segmented using T1- and T2-weighted images and a semi-automatic procedure which is described in more detail in [12 (link)] (Figure 1B). Note that T2 images were used to improve the quality of non-brain tissues.