refactor internal md_zvarstd2
refactor internal md_zvarstd2

sidward/bart,sdimoudi/bart,sdimoudi/bart,mrirecon/bart,mrirecon/bart,sidward/bart,mrirecon/bart,mrirecon/bart,sidward/bart,sidward/bart,mrirecon/bart,sdimoudi/bart,sidward/bart,sdimoudi/bart,sdimoudi/bart