5tt file, mouse brain, tracts detected only in the subcortical gray matter

Dear Francesca,
I am currently trying manually segmentation for mouse brain to create 5tt file. However I got problem with identify WM, GM, sub-cortical GM. How did you deal with that?
I based on a atlas and a segmentation results retrieved from internet, but that’s not enough for accurately segmentation.
And Could you describe more about how to create 4D 5TT file?