Creating an open source electromagnetic tracking platform

Abstract

This thesis describes the design, development and testing of Anser, the world’s first open electromagnetic tracking (EMT) platform for use in minimally invasive and image-guided interventions; Anser EMT. The goal of this work is to advance the state of the art of electromagnetic tracking systems by creating an open-source electromagnetic tracking platform for pre-clinical research and development. The specific application of this work is in bronchoscopy, where accurate navigating and targeting in the outer airways for the diagnosis and staging of lung cancer using endoscopic technology is a key unmet clinical need. A review of electromagnetic navigation and its use in bronchoscopy is included. Different imaging modalities are compared and discussed, which give rise to the need for electromagnetic tracking for navigation in the outer airways. Commercially available bronchoscopy systems are highlighted and their current drawbacks are discussed. A review of the underlying principles of electromagnetic tracking is then performed. The review enables the partitioning of an electromagnetic tracking system into independent modules. The modules are implemented as a general software framework in the Python programming language. The framework is applied to the Anser EMT platform with accuracy and performance experiments described. The hardware composition of Anser is then described in detail. A previous system design is summarised and an improved circuit design is presented. The area footprint of the revised system is reduced by approximately 75%, with significant improvements in power supply efficiency also described. The Anser system is used to address some shortcomings of commercially available electromagnetic tracking systems. Detection of metallic distortion in the clinical environment is successfully demonstrated. Experimental results show that the modified field generator is capable of detecting the severity, material type and approximate location of distorters near the field generator, a feature which commercially available systems do not provide. An exploration of modular field generator designs is then performed by combining two Anser systems. Extended tracking and enhanced accuracy is demonstrated using combined field generator configurations. The integration of electromagnetic in surgical instruments is explored through the design of custom electromagnetic tracking coils for use with the Anser system. A number of hand-wound coils were designed and tested to successfully track laparoscopic and endoscopic instruments with accuracies on-par with commercially available sensors. Lastly, Anser is demonstrated in a live, pre-clinical setting for electromagnetic navigation bronchoscopy. An electromagnetically tracked catheter was used with Anser to successfully target phantom tumours with minimum and maximum targeting errors of 7.2mm and 19.6mm respectively.