Electromagnetic tracking using modular, tiled field generators

Electromagnetic tracking (EMT) systems play an important role in medicine, robotics, and virtual reality applications by providing accurate position and orientation referencing within a fixed volume around a magnetic field generator. Advances in sensor technology provide increasingly small, lightweight sensors capable of being integrated into hand-held devices for medical simulation, gaming, and image-guided surgery. The need for customizable tracking volumes becomes of interest as the uptake of EMT technology increases. This paper proposes a new method of creating custom tracking volumes from multiple planar field generators. A monolithic, low-cost printed circuit board design allows for tiling of multiple generators to create a larger tracking volume. Experiments were performed with two generators at different angles. Successful tracking is demonstrated with increased positional accuracy observed when transmitters are inclined with respect to one another. Horizontal tiling configurations are most accurate when a common edge is shared between adjacent field generators

Planar body-mounted sensors for electromagnetic tracking

Electromagnetic tracking is a safe, reliable, and cost-effective method to track medical instruments in image-guided surgical navigation. However, patient motion and magnetic field distortions heavily impact the accuracy of tracked position and orientation. The use of redundant magnetic sensors can help to map and mitigate for patient movements and magnetic field distortions within the tracking region. We propose a planar inductive sensor design, printed on PCB and embedded into medical patches. The main advantage is the high repeatability and the cost benefit of using mass PCB manufacturing processes. The article presents new operative formulas for electromagnetic tracking of planar coils on the centimetre scale. The full magnetic analytical model is based on the mutual inductance between coils which can be approximated as being composed by straight conductive filaments. The full model is used to perform accurate system simulations and to assess the accuracy of faster simplified magnetic models, which are necessary to achieve real-time tracking in medical applications

Inductive sensor design for electromagnetic tracking in image guided interventions

As the importance and prevalence of electromagnetic tracking in medical and industrial applications increases, the need for customized sensor design has escalated. This work focuses on AC-based electromagnetic tracking systems where off-the-shelf inductive sensors may not be optimal for many medical instruments or tracking applications. We present a repeatable approach for the design, optimisation and implementation of air-core and ferrite-core inductive sensors suitable for AC-based electromagnetic tracking. Coil-based sensors were designed and tested to investigate the effect of the usual coil parameters such as turn count, geometry and core material on sensor tracking accuracy and precision. Our methodologies were experimentally validated using the Anser EMT system which enabled rapid experimental deployment. Experimental performance is reported compared to off-the-shelf sensors. Static tracking errors of less than 2mm were achieved and close correlation with theoretical design sensitivity and precision was observed. This work may represent a valuable tool in the design of bespoke sensors for electromagnetic tracking where customize sensitivity and form factor are critical

Navigational bronchoscopy for early lung cancer: a road to therapy

Peripheral lung nodules remain challenging for accurate localization and diagnosis. Once identified, there are many strategies for diagnosis with heterogeneous risk benefit analysis. Traditional strategies such as conventional bronchoscopy have poor performance in locating and acquiring the required tissue. Similarly, while computerized-assisted transthoracic needle biopsy is currently the favored diagnostic procedure, it is associated with complications such as pneumothorax and hemorrhage. Video-assisted thoracoscopic and open surgical biopsies are invasive, require general anesthesia and are therefore not a first-line approach. New techniques such as ultrathin bronchoscopy and image-based guidance technologies are evolving to improve the diagnosis of peripheral lung lesions. Virtual bronchoscopy and electromagnetic navigation systems are novel technologies based on assisted-computerized tomography images that guide the bronchoscopist toward the target peripheral lesion. This article provides a comprehensive review of these emerging technologies

Automated balloon control in resuscitative endovascular balloon occlusion of the aorta (REBOA)

Objective: The goal of this work was to demonstrate technical feasibility of automated balloon pressure management during REBOA in the pre-clinical setting. Methods: This paper presents an intelligent balloon management device which automates the balloon inflation process, preventing the possibility of balloon over or under inflation, optimizes inflation pressure and if indicated, deflates automating partial REBOA to allow distal organ perfusion. Edwards TruWave pressure transducers are used to monitor the blood pressure proximal and distal to the balloon, as well as the internal balloon pressure. A faux PID controller, implemented on an Arduino platform, is used in a feedback control loop to allow a user defined mean arterial pressure setpoint to be reached, via a syringe driver which allows intelligent inflation and deflation of the catheter balloon. Results: Ex vivo testing on a vascular perfusion simulator provided the characteristic behavior of a fully occluded aorta, namely the decrease of distal pressure to zero. In vivo testing on live porcine models indicated that automated partial REBOA is achievable and by enabling partial occlusion may offer improved medical outcomes compared to manual control. Conclusion: Automated balloon pressure management of endovascular occlusion is feasible and can be successfully implemented without changes on current clinical workflows. Significance: With further development, automated balloon management may significantly improve clinical outcomes in REBOA

An open electromagnetic tracking framework applied to targeted liver tumour ablation

Purpose: Electromagnetic tracking is a core platform technology in the navigation and visualisation of image-guided procedures. The technology provides high tracking accuracy in non-line-of-sight environments, allowing instrument navigation in locations where optical tracking is not feasible. EMT can be beneficial in applications such as percutaneous radiofrequency ablation for the treatment of hepatic lesions where the needle tip may be obscured due to difficult liver environments (e.g subcutaneous fat or ablation artefacts). Advances in the field of EMT include novel methods of improving tracking system accuracy, precision and error compensation capabilities, though such system-level improvements cannot be readily incorporated in current therapy applications due to the ‘blackbox’ nature of commercial tracking solving algorithms. Methods: This paper defines a software framework to allow novel EMT designs, and improvements become part of the global design process for image-guided interventions. An exemplary framework is implemented in the Python programming language and demonstrated with the open-source Anser EMT system. The framework is applied in the preclinical setting though targeted liver ablation therapy on an animal model. Results: The developed framework was tested with the Anser EMT electromagnetic tracking platform. Liver tumour targeting was performed using the tracking framework with the CustusX navigation platform using commercially available electromagnetically tracked needles. Ablation of two tumours was performed with a commercially available ablation system. Necropsy of the tumours indicated ablations within 5 mm of the tumours. Conclusions: An open-source framework for electromagnetic tracking was presented and effectively demonstrated in the preclinical setting. We believe that this framework provides a structure for future advancement in EMT system in and customised instrument design

Peripheral tumour targeting using open-source virtual bronchoscopy with electromagnetic tracking: a multi-user pre-clinical study

Objectives: The goal was to demonstrate the utility of open-source tracking and visualisation tools in the targeting of lung cancer. Material and methods: The study demonstrates the first deployment of the Anser electromagnetic (EM) tracking system with the CustusX image-guided interventional research platform to navigate using an endobronchial catheter to injected tumour targets. Live animal investigations validated the deployment and targeting of peripheral tumour models using an innovative tumour marking routine. Results: Novel tumour model deployment was successfully achieved at all eight target sites across two live animal investigations without pneumothorax. Virtual bronchoscopy with tracking successfully guided the tracked catheter to 2–12 mm from the target tumour site. Deployment of a novel marker was achieved at all eight sites providing a reliable measure of targeting accuracy. Targeting accuracy within 10 mm was achieved in 7/8 sites and in all cases, the virtual target distance at marker deployment was within the range subsequently measured with x-ray. Conclusions: Endobronchial targeting of peripheral airway targets is feasible using existing open-source technology. Notwithstanding the shortcomings of current commercial platforms, technological improvements in EM tracking and registration accuracy fostered by open-source technology may provide the impetus for widespread clinical uptake of electromagnetic navigation in bronchoscopy

Creating an open source electromagnetic tracking platform

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

Distorter characterisation using mutual inductance in electromagnetic tracking

Electromagnetic tracking (EMT) is playing an increasingly important role in surgical navigation, medical robotics and virtual reality development as a positional and orientation reference. Though EMT is not restricted by line-of-sight requirements, measurement errors caused by magnetic distortions in the environment remain the technology’s principal shortcoming. The characterisation, reduction and compensation of these errors is a broadly researched topic, with many developed techniques relying on auxiliary tracking hardware including redundant sensor arrays, optical and inertial tracking systems. This paper describes a novel method of detecting static magnetic distortions using only the magnetic field transmitting array. An existing transmitter design is modified to enable simultaneous transmission and reception of the generated magnetic field. A mutual inductance model is developed for this transmitter design in which deviations from control measurements indicate the location, magnitude and material of the field distorter to an approximate degree. While not directly compensating for errors, this work enables users of EMT systems to optimise placement of the magnetic transmitter by characterising a distorter’s effect within the tracking volume without the use of additional hardware. The discrimination capabilities of this method may also allow researchers to apply material-specific compensation techniques to minimise position error in the clinical setting