afni.nimh.nih.gov

If that is an anatomical mask, that's great.

In either case, the mask should be at the resolution of your
statistical data. Are your stats at 1x1x1? We generally
suggest something closer to the EPI resolution (often 3x3x3
or maybe 2x2x2).

Is your mask of just the brain or the whole volume?

690 does seem a little too large given my computations, but
not crazy.

What are the 2 lines of output from "afni -ver"?

- rick