Confusing problem about MNI brain with different dimension

I have asked this question in a different way before probably I didn’t do a good job with my line of question.

I used the cluster function to find peak voxels in my zmap data (processed by someone else). My problem is the data was processed in Freesurfer and the output image was in MNI space with dimension 256 * 256 * 256. The output of the cluster function are the voxel index and I use that to identify the MNI coordinates in fsl.

There is one problem with this, the dimension of the MNI template in fsl is 182 * 218 * 182, that means if I have a voxel coordinate index of 244 * 236* 244 in my zmap, the corresponding MNI output may be outside of the brain.

I noticed this development when I tried to visualize my data and some of the spots were slightly outside a template brain with my brainet viewer.

Does anyone have any idea about how to deal with the situation ? and I hope my problem is well understood.

FSL’s cluster can also output coordinates in millimeter instead of voxel using the --mm option.