OPT: Improved register_graymatter (not optimal yet but much better)
OPT: Improved register_graymatter (not optimal yet but much better)

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox