afni.nimh.nih.gov

It is possible, you can use 3dmaskdump to extract values from a volume, but you will get the whole volume in one column (or one column for each sub-brick, to be precise), so you will need to reshape the column into a matrix form. The -index option will include each voxel's i,j,k values in addition to the test results. This would make it easier for you to figure out how the output asciii format relates to the volume obtained from the ttest.

cheers,
Ziad