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Dear freesurfer community,

concerning interhemispheric registration: What are differences between mris_left_right_register and the xhemi pipeline (including the fsaverage_sym subject)? I understand that xhemi/fsaverage_sym are meant to provide an unbiased reference as opposed to simply mapping all data to one hemisphere.

I am trying to map a label from one hemisphere to the other on individual subjects. I noticed that mris_left_right_register results in output quite different from using fsaverage_sym via the xhemi process as an intermediate. As an example, see the figure file attached (original label on rh, mapped labels on lh). At the first glance, the output of mris_left_right_register seems to align with the curvature a lot better...

For reference, the following code was used. Is that correct?
surfreg --s ${subject} --t fsaverage_sym
surfreg --s ${subject} --t fsaverage_sym --lh --xhemi
mris_apply_reg \
  --src-label rh.label --trg rh_on_lh.xhemi.label \
  --streg ${SUBJECTS_DIR}/${subject}/xhemi/surf/lh.fsaverage_sym.sphere.reg ${SUBJECTS_DIR}/${subject}/surf/lh.fsaverage_sym.sphere.reg

mris_left_right_register \
  ${SUBJECTS_DIR}/${subject}/surf/lh.sphere \
  ${SUBJECTS_DIR}/${subject}/surf/rh.sphere \
  ${SUBJECTS_DIR}/${subject}/surf/lh.sphere.left_right \
  ${SUBJECTS_DIR}/${subject}/surf/rh.sphere.left_right
mris_apply_reg \
  --src-label rh.label --trg rh_on_lh.left_right.label \
  --streg ${SUBJECTS_DIR}/${subject}/surf/rh.sphere.left_right ${SUBJECTS_DIR}/${subject}/surf/lh.sphere.left_right

Thank you and
with best wishes
Cornelius