Electromagnetic Tracking of Elongated Sensors for Endoscopic Navigation

Abstract

As the prevalence of image-guided interventions increases, electromagnetic tracking (EMT) systems play an important role in modern patient care, as they enable real-time instrument positioning and navigation inside the human body without line-of-sight restrictions. Miniature-size inductive coils are the gold standard in clinical settings, as they provide accurate, passive sensing of the magnetic field. To compensate for their small dimensions, such sensors are designed with an elongated shape, where the coil length is usually 10 to 20 times larger than the diameter. In this article, the benefits of a field model based on the magnetic scalar potential formulation are demonstrated for EMT applications where elongated tracking sensors are used. The novel method resolves the single-point approximation error when the coil length is not negligible, and demonstrates improvements in terms of speed and storage requirements. A detailed analysis is proposed where alternative formulations of the magnetic model used in the tracking algorithm are compared. Although this work does not resolve any substantial limits of EMT used in a clinical environment, which are mainly caused by the presence of magnetic distortions, the proposed method is an improvement over existing EMT systems because it enables more accurate and faster tracking. The method might facilitate the use of longer tracking sensor coils which can achieve high sensitivities without the requirement of a magnetic core. In the envisioned application, such coils may be wound around flexible instruments, such as endoscopes or catheters.