Wireless Actuation, Imaging, and Control of Magnetic Robots with Magnetic Resonance Imaging Devices

Abstract

The magnetic actuation has been one of the promising wireless actuation methods for minimally invasive surgeries. The magnetic field and its gradients can penetrate inside the human body and provide actuation and control for wireless magnetic robots. Due to the lack of direct line-of-sight in such minimally invasive operations, one of the most important research questions towards clinical applications is the acquisition and combination of clinical imagingmodalities with wireless magnetic actuation methods.Intraoperative imaging modalities, such as magnetic resonance imaging (MRI), are employed to fulfill the need for visual feedback to the surgeons for such operations. ClinicalMRI systems are already equipped with three electromagnetic hardware systems that are used for imaging three-dimensional soft tissues. Such hardware and the generated magnetic field can also be used to actuate magnetic objects wirelessly. This MRI-powered actuation method aims to combine imaging and actuation by using a single clinical MRI system and enables a potential alternative for the future's interventional MRI (iMRI) procedures. Moreover, using MRI-powered wireless magnetic robots with image acquisition and magnetic actuation under MRI systems, minimally invasive operations can be performed neither introducing any additionalelectromagnetic hardware, nor reducing the workspace of the scanners. Therefore, the issues stemming from combining separate imaging and actuation devices are minimally present in such MRI-powered actuation techniques. Converting clinical MRI devices into a wireless robotic manipulation platform comes with some challenges. These challenges can be classified as (1) the limited actuation degrees-offreedom (DOF), (2) the implementation of medical functions with miniature MRI-powered robots, (3) MR monitoring challenges such as image distortions due to the magnetic robot material, (4) slow MR image feedback rate for such a time-multiplexed imaging and actuationmethod with the same device. In this thesis, each of these challenges is addressed and methods to overcome these challenges are proposed. By using magnetic pulling forces exerted by MRI gradient coils, not only translational but also rotational motions of miniature magnetic robots have been accomplished. We demonstrate a wireless capsule endoscope that employs both rotation and translation withonly magnetic pulling forces. Moreover, such a capsule robot is able to translate in three-dimensional volumes due to its near-buoyant design. Controlling the position or orientation of these robots via magnetic pulling forces in three-dimensional fluids is demonstrated. The translation and rotation of such capsule robots are coupled. In other words, the magnetic pulling force used for rotation may also induce a translation simultaneously. This may create difficulty in both open-loop (human-in-the-loop, teleoperation) and closed-loop (fully autonomous) control of these robots. In order to overcome this issue, a phase-changing wax material-based locking mechanism is proposed to lock and unlock the robot's orientation on-demand via wireless heating. This mechanism decouples the rotation from translation and allows the robot to translate with a fixed orientation. Medically relevant and orientation-dependent functions, such as hyperthermia and drug delivery, are also demonstrated towards the medical use of such MRI-powered robots. Additionally, two-dimensional monitoring and one-dimensional imaging/actuation systems are established for closed-loop position control andhuman-in-the-loop teleoperation applications towards minimally invasive robotic surgeries.