Design and Hierarchical Control of a Homocentric Variable Stiffness Magnetic Catheter for Multi-Arm Robotic Ultrasound-Assisted Coronary Intervention

Autonomous magnetic catheterization has become a promising technology for next-generation minimally invasive cardiovascular surgery. In this paper, a novel homocentric variable-stiffness magnetic robotic catheter (HVS-MRC) is presented. This device is controlled by a multi-arm robot-assisted catheterization system for use in radiation-free coronary ultrasound intervention. The uniqueness of the HVS-MRC is the generation of variable stiffness through the telescopic motion of three homocentric components with embedded internal magnets. These components can be used to achieve multiple curvatures and large deflections ( $>$ 120 degrees) under a magnetic wrench provided by an external mobile magnet module (EMMM) to adapt to the complex coronary environment. The variable-stiffness kinematics modeling, multivessel selection strategy, and preoperative surgical planning of the proposed magnetic robotic catheter are established. Meanwhile, an extracorporeal mobile ultrasound module (EMUM) is adopted to intraoperatively localize the catheter's in-plane motion with a dominant visual/force feedback controller. A hierarchical relative control scheme is proposed based on the relative Jacobian method to synchronize the motions of the multi-arm robot-assisted catheterization system. The overall performance is evaluated with an in vitro human-sized coronary arterial phantom with challenging anatomical variabilities. The results reveal that the HVS-MRC exhibits a high-accuracy intervention performance (average error of 1.52 $ \pm$ 0.35 mm) with smoother steering compared with conventional catheters. High synchronization with a low ultrasound target loss rate (15.8%) and constant-force tracing (2.50 $\pm$ 1.02 N) of the multi-arm robot-assisted catheterization system demonstrate promising application potential in radiation-free autonomous ultrasonographic coronary intervention operations.