Quantitative analysis of factors affecting intraoperative precision and stability of optoelectronic and electromagnetic tracking systems.

This study aims to provide a quantitative analysis of the factors affecting the actual precision and stability of optoelectronic and electromagnetic tracking systems in computer-aided surgery under real clinical/intraoperative conditions. A "phantom-skull" with five precisely determined reference distances between marker spheres is used for all measurements. Three optoelectronic and one electromagnetic tracking systems are included in this study. The experimental design is divided into three parts: (1) evaluation of serial- and multislice-CT (computed tomography) images of the phantom-skull for the precision of distance measurements by means of navigation software without a digitizer, (2) digitizer measurements under realistic intraoperative conditions with the factors OR-lamp (radiating into the field of view of the digitizer) or/and "handling with ferromagnetic surgical instruments" (in the field of view of the digitizer) and (3) "point-measurements" to analyze the influence of changes in the angle of inclination of the stylus axis. Deviations between reference distances and measured values are statistically investigated by means of analysis of variance. Computerized measurements of distances based on serial-CT data were more precise than based on multislice-CT data. All tracking systems included in this study proved to be considerably less precise under realistic OR conditions when compared to the technical specifications in the manuals of the systems. Changes in the angle of inclination of the stylus axis resulted in deviations of up to 3.40 mm (mean deviations for all systems ranging from 0.49 to 1.42 mm, variances ranging from 0.09 to 1.44 mm), indicating a strong need for improvements of stylus design. The electromagnetic tracking system investigated in this study was not significantly affected by small ferromagnetic surgical instruments.