Interventional Lorentz Force-Based Actuation under Magnetic Resonance Imaging

Interventional magnetic resonance imaging (MRI) has been a widely adopted technique for visualizing and treating life-altering conditions such as cardiovascular disease and cancer. Intervening directly within such MRI devices offers many advantages to improving patient outcomes but is currently limited due to the lack of available tools and the highly constraining environment. Different kinds of approaches have been taken over the years to remedy such concerns such as redesigning the MR scanner, migrating the machine or patient in or out of the operating room, or developing MR-compatible solutions within the workspace of the imaging device.

Remote controlled platforms have enabled interventionalists to operate on the patient intraoperatively. However, these platforms must be carefully designed to abide by safety regulations due to the strong external magnetic field imposed by the device as well as the rapidly changing electromagnetic fields during imaging. Therefore, many different kinds of actuators have been attempted for use within such systems to understand their MR-compatibility, functionality, and scalability. Of these design criteria, Lorentz force-based actuators have shown promise due to their scalability, ease of manufacturing, and high force/torque to weight ratio. However, these actuators have not been fully explored for medical devices in MR scanners due to various concerns such as resistive heating and other design considerations.Therefore, the goal of this thesis is to explore the capabilities of Lorentz force-based actuators within MR imaging devices for medical tool integration including catheters, drilling mechanisms, endoscopes, and forceps.

The first chapter of the thesis introduces the field of minimally invasive surgery including various imaging modalities, device technologies, and their associated advantages and disadvantages. It introduces the field of interventional magnetic resonance imaging, providing a brief history of magnetic resonance imaging (MRI), the various design changes that have been made to provide patient access, as well as the current state of the art. The various challenges associated with developing MR-compatible devices for use in such environments such as device materials, heating, image susceptibility, response time, and scalability are also discussed.

The second chapter of this work introduces a quad-coil design for direct integration to a catheter for endovascular steering. It touches upon utilizing Lorentz-force based steering, in which currents are applied to electromagnetic microcoils mounted on a catheter inside the very high (3-7 T), uniform, magnetic field within the MRI device. It also demonstrates the scalability of the quad-coil configuration through the design and actuation of a Lorentz force-based microcatheter. It will explain the actuation algorithm for Lorentz force-based heat-mitigated steering and power limitations using simulations for various catheter lengths and experimentation within realistic anatomical models and tissue. This chapter shows the scalability, design and safety considerations that are associated with catheter-based Lorentz actuation for use within MR-guided minimally invasive surgery.

The third chapter explores Lorentz force-actuation for use in extended medical functions such as atherectomy. This is achieved using an MR-compatible, catheter-integrated electric motor to drill through arterial calcified plaque. The fourth part of this thesis leverages the heat-mitigated algorithm to create a neuroendoscope for ventricular tumor ablation. This chapter investigates the feasibility of providing direct visualization and MR-guidance simultaneously to provide more accurate treatments. It also realizes the capabilities of integrating Lorentz force-actuators for medical forceps. The thesis concludes with a summary of the thesis contributions as well as future work to further the field of interventional Lorentz force-based magnetic resonance imaging.