this is a surfice question – not really a lead-dbs question. But surfice is pretty easy to use.
You can get it from here and there are also instructions there:
There’s also a copy installed in Lead-DBS but it’s easier to use the standalone.
There is a matlab call that will directly produce an image using surfice (simply ea_surfice(‘yourfilename.nii’)) but I’d still recommend to use the surfice standalone and add some overlays there.