afni.nimh.nih.gov

3dWarp uses the Brett transform to transform the dataset from Talairach to MNI space, but the grid (the xyz locations of all the voxels) is set by the -gridset and -newgrid options for 3dWarp. If you are warping ROIs, then you probably want to use nearest neighbor interpolation too (-NN). For some more discussion of transforming between Talairach and MNI space, see this previous thread:

http://afni.nimh.nih.gov/afni/community/board/read.php?1,70173,80922#msg-80922