Image-guided neurosurgery comparing a pointer device system with a navigating microscope: a retrospective analysis of 208 cases. - Roessler,K.; Ungersboeck,K.; Aichholzer,M.; Dietrich,W.; Czech,T.; Heimberger,K.; Matula,C.; Koos,W.T. (Minim Invasiv Neurosurg, 1998)