Comparative examination of the accuracy of a mechanical and an optical system in CT and MRT based instrument navigation.

The aim of an intraoperative instrument navigation system is to support the surgeon in the localization of anatomical regions and to guide the use of surgical instruments. An overview of technical principles and literature reports on various navigation systems is provided here. The navigation accuracy (tested on a plastic phantom under simulated operating room conditions) of the mechanical Viewing Wand system and the optical SPOCS system amounts to 1 to 3 mm for computerized tomography (CT) data, with a significant inverse dependence on the layer thickness. The values for magnetic resonance tomography (MRT) data are significantly higher. In regard to the choice of registration points, a statistically inverse dependence exists between the number of points and the distance between the points. During the time period between autumn 1993 and mid-1999, more than 120 clinical applications were performed. The intraoperative accuracy was in the range of < or = 3 mm. Registering the patient position with preoperatively inserted screw markers achieved accuracy values of < or = 2 mm. The instrument navigation technique has proved to be very advantageous for the spatial orientation of the surgeons. The possibility of checking resection borders has opened up new perspectives in tumor surgery. A quality improvement and a reduction of the operational risks as well as a considerable decline in the stress placed on the patient can be expected in the near future due the techniques of computer-assisted surgery.