Comparison of different 3D navigation systems by a clinical "user"

Three-dimensional navigation systems are routinely used in endoscopic skull base surgery neurosurgery, maxillo-facial and endoscopic sinus surgery. Th eir precision can, however, change in the course of one experiment. We have compared five different 3D navigation systems and discuss here possible re asons for the limits of system precision. A plexiglass cube an which test p oints were marked served as a test-model. Two well-trained system users mea sured the distances between the test points in each of the five systems. Th e results were compared with reference data provided by the NUMEREX(TM) dev ice at the Technical University of Vienna. The accuracy data shown by all t hese 3D navigation systems ranged from 0.0 mm to 6.67 mm. The accuracy data of a system calculated in advance did not always correspond with the syste m precision on the screen. The system precision in the center of the cube w as higher than on its surface, which made us conclude that the angle betwee n the tracker system and the pointing device touching the test point may be critical for system precision. Applying an automatic registration step did not result in greater system precision. Slice thickness and the angle of t he pointing device seem to be responsible for system precision.