I have a surface label for a region-of-interest in the right hemisphere, which I generated from a cortical thickness analysis. I am now doing an analysis on the white matter below this roi, by moving the label into volume space with mri_label2vol, and sampling below the surface with the --proj option. I want to repeat this white matter analysis in the homologous region-of-interest in the left hemisphere, as accurately as possible. I found the documentation for xhemi, and an earlier post about interhemispheric registration of rois (
https://mail.nmr.mgh.harvard.edu/pipermail/freesurfer/2012-July/024821.html), but I'm not clear on what the xhemi option does, nor what the outputs are, nor what fsaverage_sym is, and so I haven't been able to figure out how to use it for my purpose. Is there more info available somewhere on interhemispheric registration with freesurfer tools, and/or does anyone have suggestions for how I should proceed?