Two-Dimensional Robust Magnetic Resonance Navigation of a Ferromagnetic Microrobot Using Pareto Optimality

Abstract

This paper introduces a two-dimensional (2-D) autonomous navigation strategy of a 750- ${\mu \text{m}}$ steel microrobot along a complex fluidic vascular network inside the bore of a clinical 3.0-T magnetic resonance imaging (MRI) scanner. To ensure successful magnetic resonance navigation of a microrobot along consecutive channels, the design of autonomous navigation strategy is needed, taking into account the major MRI technological constraints and physiological perturbations, e.g., nonnegligible pulsatile flow, limitations on the magnetic gradient amplitude, MRI overheating, and susceptibility artifacts uncertainties. An optimal navigation planning framework based on Pareto optimality is proposed in order to deal with this multiple-objective problem. Based on these optimal conditions, a dedicated control architecture has been implemented in an interventional medical platform for real-time propulsion, control, and imaging experiments. The reported experiments suggest that the likelihood of controlling autonomously untethered 750- ${\mu \text{m}}$ magnetic microrobots is rendered possible in a complex 2-D centimeter-sized vascular phantom. The magnetic microrobot traveled intricate paths at a mean velocity of about 4 $\text{mms}^{-1}$ with average tracking errors below 800 ${\mu \text{m}}$ with limited magnetic gradients $\pm \text{15} \text{mTm}^{-1}$ , which is compatible with clinical MRI scanners. The experiments demonstrate that it is effectively possible to autonomously guide a magnetic microrobot using a conventional MRI scanner with only a software upgrade.