Navigation of Untethered Small-Scale Helical Devices Using Magnetic System Under Ultrasound Guidance

Magnetic actuation of untethered small-scale helical devices (USHDs) shows great potential for targeted drug delivery or as minimally invasive surgical tools in the human body. However, ensuring the success of therapeutic interventions in anatomically challenging regions, such as neck vascular networks with winding pathways and branching, demands the incorporation of precise image feedback and a robust control method. How to construct a control method with precise navigation ability in complex and hard-to-reach body districts is still a challenging work. In this paper, we propose a closed-loop control strategy for the USHD based on a permanent-magnet robotic (PMR) system inside a three-dimensional (3-D) vascular model with blood. First, the 3-D vascular model is reconstructed using 2-D ultrasound images. Second, the point-to-point closed-loop control of the USHD is performed under ultrasound guidance, and the control input is obtained to act on both the PMR system and the ultrasound system. Next, the USHD navigates the different pathways of the 3-D vascular model under the proposed control strategy. Finally, our in vitro experimental results indicate that the maximum mean absolute position error between the target point of each branch and the actual position reached by the USHD (length and diameter of 6 mm and 1.5 mm, respectively) is 6.4±3.8 mm and 4.2±2.8 mm when the blood flow rate is 16.6 mL/min, which corresponds to 28% of the maximum venous flow rate.