afni.nimh.nih.gov

Hi all,
I want to divide the superior colliculus (SC) into different layers according to the physical distance from each voxel in SC to the surface.That is,I want to make ROIs of different depth from the surface of the SC.The depth for each voxel in the SC will be calculated as the shortest distance from the voxel to all surface voxels.I would like to know if there are some other ways to make the ROIs except for manually drawing different layers?
Yu Zhang
Thank you!