how to obtain gray matter volume

Hi, Yan,
Can I use REST to obtain regional gray matter volume (e.g. PCC) with a binary mask. I mean real volume rather than mean "volume" in that area. If I need the codes;could you tell me what is the code in REST.
Great thanks!

In your question, I suppose you already got the grey matter volume map for the whole brain, didn't you?
If so, you can just apply a PCC binary mask onto this grey matter volume map by using REST image calculator (i1.*i2), 
then, in matlab, you use [data head] = rest_ReadNiftiImage(imageIN) to read the result into matlab (store in "data" for example),
then, use sum(data) to calculate real volume of the PCC. 
I don't know if I understood you correctly.