I want to create a mask of all subjects and sessions in my study. I have 80 subjects who have resting state scans at two time points. Data have been preprocessed and warped into template space. I’d like to create a mask that includes voxels from all subjects and sessions. In other words, I’d like to mask out any voxels where there isn’t data available for everyone at both time points. Can anyone please recommend a good way to do this?