ERROR COMPENSATION FOR DEVICE TRACKING SYSTEMS EMPLOYING ELECTROMAGNETIC FIELDS

The present invention is capable of more accurately tracking an invasive device in a subject's body in the presence of eddy current inducing structures. Current patterns applied to the tracking system's transmit coils are modified to compensate for the effect of the eddy currents. The current supplied to the coils is a linear combination of the current needed to create the desired electromagnetic field in the region of interest; and one or more error terms. These terms are determined experimentally during system calibration and are mathematically modeled as a series of exponential functions having a given amplitude and time constant. The error terms in the current applied to the transmit coils cancel the magnetic fields created by eddy currents within the tracking region and result in an actual electromagnetic field which is close to the desired ideal electromagnetic field. The fidelity of the electromagnetic field is further increased by reducing eddy currents within the eddy current inducing structures. This is done by constructing shield coils which are placed between the transmit coil and the eddy current inducing structures. These shield coils create canceling magnetic fields within the eddy current inducing structures without substantially altering the electromagnetic fields in the region over which the invasive device is tracked.