Dear Freesufer experts,

I am wondering if it is possible to tell mri_vol2surf to ignore certain voxels in the src volume, for instance, by setting their intensity to -999.  

I'm trying to project only gray matter voxels from a PET scan onto the fsaverage surface, but when I use an only-GM PET image as the src, the zeroed-out WM/CSF voxels are occasionally projected onto the surface (with --interp nearest).

Any suggestions?

Thanks!

Kate