关于MASK，请教，十分感谢！

在你们的文章中写到：“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. ”（Human Brain Mapping 2012） 想请问：这里的0.2是指什么值，这种设定MASK的做法是在MRIcro--ROI--Apply intensity filter to volume中做的吗? 该做法能否应用于设置WM MASK？ 其他文献中有提到的做法是：”The resulting segmented WM and CSF images were then thresholded to ensure 80% tissue type probability. “这种做法和你们采用的是否一致？