Dear SPM users,
I recently learned that the default of SPM for counting voxels per a cluster is set to 18(edge) at spm_bwlabel. This may mean that the area wouldn't show up in the SPM result table unless the number of voxel surrounding the center coordinate is
at least 18, I assume if I set the extent k value to 1.
Then, presumably, the number of voxel in the cluster size 2 should be around 36 (18*2), size 3 be 54(18*3), and so on.
In fact, I extract one particular cluster using Marsbar, the number of voxels within the cluster is quite different (e.g., at the region whose cluster size is 5, the number of voxels is only 11, not 90) .
Can anyone tell me how this could happen?
Thanks,
YSL
