Read the transformation matrix that SPM and FreeSurfer write into the .mat file next to an ANALYZE
image, and convert it to the convention used by this package (0-based voxel indices, right-anterior-superior
world coordinates). See the geometry section of read.fs.volume.analyze for the details.
analyze.mat.sidecar.to.vox2ras(matfile)named list with the entries vox2ras (a 4x4 numeric matrix, or NULL if the file could not be read or
contains no usable matrix) and reason (a character string describing the problem, or NULL on success).
character string, the path of the .mat file.