Modeling and Design of Magnetic Surgical Instruments for Minimally Invasive and Image-Guided Applications

Magnetic continuum robots offer a promising route to safer and more dexterous endoluminal interventions. By exploiting external magnetic fields for actuation, these devices can remain miniaturized, compliant, and capable of navigating tortuous anatomy. This dissertation investigates how actuation principles, magnetic materials, and imaging modalities can be combined to design surgical instruments that are miniaturized, precisely controllable, and compatible with clinical workflows.

The first contribution of this work introduced breathing-compensated magnetic shape forming of a continuum robot for robotic bronchoscopy. A rigid-link model was used to optimize torque-based actuation between peak inhalation and exhalation. Validation in a dynamic lung phantom demonstrated consistent targeting of peripheral branches with root-mean-square errors below 2.5 mm. While optical tracking was used for validation, the approach is extendable to fluoroscopy-based segmentation in clinical practice. This established the principle of physiology-aware magnetic actuation in pulmonary interventions.

The second contribution investigated magnetic resonance imaging (MRI) as both an imaging and actuation platform. A tethered guidewire with a low-carbon steel bead at its tip was actuated using the gradient coils of a 7 T pre-clinical MRI scanner, capable of up to 660 mT/m gradient strength. The bead was pulled through phantoms with radii of curvature as small as 15 mm, after which a silicone sleeve was deployed to establish a stable guidewire. Systematic evaluation of bead size and material revealed the trade-off between actuation force and MRI visibility: larger beads produced stronger forces but also larger susceptibility-induced voids in the MR images, in some cases exceeding 8 mm.

This represented the first demonstration of gradient-pulled tethered devices within MRI and quantified the balance between navigation performance and imaging compatibility. The final contribution presented the Coaxial Sleeve Magnetic Actuator (CoSMA), an MRI-actuated concentric tube catheter that uses soft-magnetic ferrous rings to exploit the easy-axis phenomenon of the static MRI background field. A 3 mm prototype achieved retroflexion, sigmoidal bending, and traversal of all five branches of an aortic arch phantom. Optical tracking confirmed bending angles over 120°, while MRI reconstructions visualized the characteristic plume-shaped voids produced by the rings. Rigid-link modeling predicted device shapes with less than 5% error. This was the first demonstration of torque-based shape forming in MRI and established a pathway to MRI-compatible magnetic catheters.

Collectively, these studies demonstrate a systematic progression: beginning with physiology aware torque actuation, advancing to MRI-based gradient pulling, and culminating in torque-based shape forming in MRI. The results highlight three overarching design principles: miniaturization through external actuation, precise controllability enabled by accurate modeling, and integration with MRI to unify imaging and actuation. These contributions advance the field of magnetic surgical robotics and provide a foundation for future instruments that are slender, dexterous, and fully integrated into image-guided surgery.