SYNOPSIS:
   GETSTATS [set]

DESCRIPTION:
    Get statistics info for a given set.

RETURN CODE:
    Returns a struct containingthe following members:
    rc.count  : Number of voxels found.
    rc.min    : Minimum value found.
    rc.max    : Maximum value found.
    rc.average: Average value.
    rc.sigma  : Estimated sigma.
