Design, Actuation, and Control of an MRI-Powered Untethered Robot for Wireless Capsule Endoscopy

Abstract

Magnetic resonance imaging (MRI)-powered magnetic robotics aims to convert clinical MR scanners into a remote robotic manipulation platform to provide an alternative approach for interventional MRI procedures. The presence of the main magnetic field ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> ) inside of MRI systems imposes magnetic constraints. Because of this static and strong magnetic field, many magnetic actuation techniques to orient or rotate magnetic objects are not feasible under MRI. Therefore, the robot design and actuation methods should consider these constraints for the intended medical applications. A free-to-rotate robot design could be utilized under MRI for providing rotational motion with magnetic pulling. However, the coupled translation with rotation induces difficulty in control of these robots, especially for camera pointing towards capsule endoscopy. In this study, we present a wireless magnetic robot that exploits a surface contact to create a rotation around a contact point with minimal translation. The proposed robot is integrated with a camera and an on-board battery for endoscopy purposes. The robot's tuned density also allows three-dimensional (3D) navigation to visually scan the workspace. We also demonstrate the open- and closed-loop actuation and control performance to explore the range of pitch angles accomplishable and closed-loop feedback control accuracy by using visual feedback. The closed-loop control experiments have shown 0.19 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> of steady-state error with 1.9 seconds rise time and 20% overshoot. Thanks to the surface contact during orientation control, the worst-case undesired translation is found to be 6.7 mm. Such robot provides the first steps towards active capsule endoscopy actuated by MRI devices for combining physiological images from an MRI device and the auxiliary visual camera images via the capsule robot to diagnose certain diseases in the gastrointestinal (GI) tract.