Hello SPM experts!

I have a mask of the rostral anterior cingulate superimposed on a Gray
Matter mask. They are in original space. I was able to extract the rostral
ACC mask from the gray matter mask and binarize it.

I now want to convert this mask to MNI space. I am rather new to SPM. One
way I thought to do do this was to use the forward deformation file
(y_T1.nii) and apply to the mask. This did not work fact I can no
longer see my mask!

Another option I thought about was to normalize the gray matter mask to MNI
space (same as before, apply the forward deformation), and then extract the
ROI, thinking that may produce more accurate results. This did not work
either.  And, if I binarize the entire gray matter mask, I can no longer
differentiate the rostral ACC mask from the rest of the gray matter.
Before, the gray matter was a 1, non-gray matter was a 0, and the rostral
ACC mask was a 2, so I could easily extract the mask.

I saw that at least in earlier spm versions, there would be .mat files
produced that contained the original to MNI warp matrix and the MNI to
original warp matrix. I don't see those files in my SPM12 output.

Any guidance on how to do this in SPM?