Optimal measurements in magnetic tracking for organ-positioning during radiotherapy

Other conference contribution, 2011

In a magnetic tracking system, the position and orientation of a coil is determined by its low frequency (LF) magnetic interactions with a coil array of known position and orientation. There are two main types of systems: (i) the coil with unknown position works as a transmitter with a receiving array of sensors, or (ii) the coil array is the transmitter and the coil with unknown position is used as sensor. As LF magnetic fields do not interact with the human body, magnetic tracking is particularly well-suited for tracking of objects in and around the human body. For example, this tracking technique has in recent years been proposed for eye tracking, tracking of tongue movements, and organ-positioning during radiotherapy. We focus on an organ-positioning system for use during radiotherapy. The system, which is of type (i) above, consists of a transmitter that is implanted near the organ of interest and an external array of sensors. Of particular interest is the spatial layout of the sensor array, since this strongly influences the performance of the tracking system. A well-designed sensor array will give good positioning accuracy whereas an ill-designed array can result in an unsolvable positioning problem. In this work, we use Fisher-information theory from the field of optimal measurements to formulate an optimization problem for the layout of the sensor array. Furthermore, we solve the optimization problem and discuss the implications of the results on the design of magnetic tracking systems.