Crossing-Lines Registration for Direct Electromagnetic Navigation.

Direct surgical navigation requires registration of an intraoperative imaging modality to a tracking technology, from which a patient image registration can be found. Although electromagnetic tracking is ergonomically attractive, it is used less often than optical tracking because its lower position accuracy offsets its higher orientation accuracy. We propose a crossing-lines registration method for intraoperative electromagnetic tracking that uses a small disposable device temporarily attached to the patient. The method exploits the orientation accuracy of electromagnetic tracking by calculating directly on probed lines, avoiding the problem of acquiring accurately known probed points for registration. The calibration data can be acquired and computed in less than a minute (50 s +/- 12 s). Laboratory tests demonstrated fiducial localization error with sub-degree and sub-millimeter means for 5 observers. A pre-clinical trial, on 10 shoulder models, achieved target registration error of 1.9 degree +/- 1.8 degree for line directions and 0.8 mm +/- 0.6 mm for inter-line distance. A Board-certified orthopedic surgeon verified that this accuracy easily exceeded the technical needs in shoulder replacement surgery. This preclinical study demonstrated high application accuracy. The fast registration process and effective intraoperative method is promising for clinical orthopedic interventions where the target anatomy is small bone or has poor surgical exposure, as an adjunct to intraoperative imaging.