Real-Time Navigation of an Untethered Miniature Robot Using Mobile Ultrasound Imaging and Magnetic Actuation Systems

Remotely actuated small-scale robots have shown promising capabilities in targeted delivery, micromanipulation, and biosensing. However, challenges remain in imaging and control of a robot in a large workspace, especially when conducting targeted navigation in hard-to-reach and tortuous regions of a living body. In this work, we propose a strategy for real-time magnetic navigation of an untethered miniature robot in a large workspace using ultrasound image feedback. A mobile electromagnetic coil-based system is designed to control and simultaneously track the robot in a large working space. An ultrasound probe is integrated with a three degree-of-freedom (DoF) manipulator to sweep the workspace and actively follow the miniature robot, where a dynamic region of interest (ROI) is applied to track the robot in real-time. Experiments in two tissue-mimicking phantoms with branching and tortuous environments are respectively conducted. Results demonstrate that the robot can selectively navigate along different paths of the branching environment, and it also exhibits long-distance navigation in a tortuous environment. The mean transverse deviations between the planned trajectory and tracking position are less than the radius of the tube, and the mean tracking intervals are less than half body length of the robot. These results validate the feasibility of the mobile ultrasound-integrated navigation strategy, demonstrating a potential approach for navigating a miniature robot inside hard-to-reach regions under medical imaging guidance.