Freehand cocalibration of optical and electromagnetic trackers for navigated bronchoscopy

Abstract

Recent technical advances in electromagnetic (EM) tracking have facilitated the use of EM sensors in surgical interventions. Due to the susceptibility to distortions of the EM field when placed in close proximity to metallic objects, they require calibration in situ to maintain an acceptable degree of accuracy. In this paper, a freehand method is presented for calibrating electromagnetic position sensors by mapping the coordinate measurements to those from optical trackers. Unlike previous techniques, the proposed method allows for free movement of the calibration object, permitting C2 continuity and interdependence between positional and angular corrections. The proposed method involves calculation of a mapping from (ℝ3,SO(3)} to {ℝ3,5O(3)} with radial basis function interpolation based on a modified distance metric. The system provides efficient distortion correction of the EM field, and is applicable to clinical situations where a rapid calibration of EM tracking is required. © Springer-Verlag 2004.