A novel fully automatic system for the evaluation of electromagnetic tracker

Electromagnetic tracking (EMT) systems are gaining increased attention in various fields of image-guided surgery. One of the main problems related to EMT systems is their vulnerability to distortion due to metallic objects. Several methods have been introduced to evaluate electromagnetic trackers, yet, the data acquisition has to be manually performed in a time consuming procedure, which often leads to a sparse volume coverage. The aim of this work is to present a fully automatic calibration system. It consists of a novel, parallel robotic arm and has the potential to collect a very large number of tracking data while scanning the entire tracking volume of a field generator. To prove the feasibility of our system, we evaluate two electromagnetic field generators (NDI Planar and Tabletop) in an ideal metal-free environment and in a clinical setup. Our proposed calibration robot successfully performed throughout the experiments and examined 1,000 positions in the tracking volume of each field generator (FG). According to the results both FGs are highly accurate in an ideal environment. However, in the examined clinical setup, the Planar FG is strongly distorted by metallic objects. Whereas the Tabletop FG provided very robust and accurate tracking, even if metallic objects where lying directly underneath the FG.