Temporal Bone Segmentation

What is the best method for segmenting the temporal bone from a CT for 3D printing? I’m having a lot of trouble with the mastoid air cells, there’s always a hole in the pietrous part of the temporal all the way through the mastoid and out of the skull.
I don’t know if this happens only because the resolution is poor, I’ve downloaded DICOM files trom TCIA and they are very old(1999, the newest is from 2003).
Any advice is welcomed.
Thank you.