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Freehand Cocalibration of Optical and Electromagnetic Trackers for Navigated Bronchoscopy

Adrian Chung, Philip Edwards, Fani Deligianni, Guang-Zhong Yang

Conference or Workshop Paper
Medical Imaging and Augmented Reality (MIAR 2004): Second International Workshop

Recent advances in electromagnetic (EM) tracking technology have facilitated the use of EM sensors in surgical interventions. Due to the susceptibility to distortions in the EM field when placed in close proximity to metallic objects, they require on site calibration to maintain an acceptable degree of accuracy. In this paper, a freehand method is presented for calibrating an electromagnetic position sensor by mapping the coordinate measurements to those from an optical tracker. The EM tracker provides 5 or 6 degree of freedom (DOF) measurements, incorporating 2 or 3 angular measurements as well as 3D position. Unlike previous techniques, the proposed technique allows for free movement of the calibration object, provides C^2 continuity and allows interdependence between positional and angular correction. This involves calculation of a mapping from {IR^3, SO(3)} to {IR^3, SO(3)}. Radial basis function interpolation with a modied distance metric to calculate this 6D-6D mapping. A calibration tool has been constructed to take either the 5 or 6 DOF EM trackers in several accurately milled positions that enable the full range of angles to be covered and graphical software guides the user to help achieve adequate coverage of the 6D space. The system provides a quick and easy way of correction for distortion in the EM field. The methods are applicable to situations where a rapid calibration of EM tracking is needed, such as those for in vivo bronchoscope tracking.

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