Accuracy of optical localizers for computer aided surgery

Abstract

The localization of surgical tools and the patient's reference coordinate system in three to six degrees of freedom is one of the key technologies in computer aided surgery. Several tracking methods are available, among which optical tracking is the most widespread in clinical use. Optical tracking technology has well proven to be a reliable method for intra-operative position and orientation acquisition for many clinical applications. However, the accuracy of these localizers is still a topic of discussion. In this paper, the accuracy of three optical localizer systems, the NDI Polaris P4, NDI Polaris Spectra (active and passive mode) and the Stryker Navigation System II Camera, is assessed and critically compared. Static tests revealed that only the Polaris P4 shows a significant warm up behavior with a significant shift of accuracy within 42 minutes after switching it on. Furthermore, the intrinsic localizer accuracy was determined for single markers as well as for typical tools using a volumetric measurement protocol on a coordinate measurement machine. To determine the relative distance error within the measurement volume, the Length Measurement Error (LME) was determined at 35 test lengths. The two active localizer systems, the Stryker Navigation System II camera and the Polaris Spectra (active mode), showed the best results with a trueness of 0.058±0.033mm and 0.089±0.061 mm, respectively (mean±std. dev.). The Polaris Spectra (passive mode) showed a trueness of 0.170±0.090mm and the Polaris P4 showed the lowest trueness with 0.272±0.394mm and a higher number of outliers than all the other cameras.