关于灰质mask

老师们好:
在老师们实验室的文章(Wang ZQ,et al ,2011, HBM)做mALFF时提到“The global mean ALFF value was calculated for each participant within a group GM mask obtained by selecting a threshold of 0.2 on the mean GM map of all 54 subjects.”  这里是不是意味着在DPASFA中,做ALFF+fALFF前选的mask应该为自己定义的灰质mask?