Active Electromagnetic Tracking System With Directionally Uniform and High Accuracy Using 2-DoF Orientation Control of the Magnetic Source

Electromagnetic tracking, as a non-contacting and occlusion-free localization method, has been widely used to track various intracorporeal medical devices and robots in minimally invasive medicine. Although it is well known that the magnetic sensitivity and tracking accuracy deteriorates with the distance between the sensor and the magnetic source, the dependence of tracking accuracy on the direction of the sensor relative to the electromagnet is long overlooked. In this paper, the directional variation of magnetic sensitivity and tracking accuracy is analytically investigated. A novel representation of the magnitude of magnetic sensitivity (i.e., the determinant of magnetic measurement Jacobian) is proposed to quantify and predict the tracking accuracy. It is demonstrated that the magnetic sensitivity to position is the highest when the sensor is located exactly on the magnetic moment axis of the electromagnet, and it decreases as the sensor moves to the side of the electromagnet. Therefore, to maintain directionally uniform and high accuracy around the electromagnet, an active tracking system is developed by controlling the orientation of the electromagnet such that its magnetic moment axis is always pointed towards the sensor. The active tracking system is experimentally validated with uniformly high position tracking accuracy around 3 mm in all directions around the electromagnet.