Thesis Format

Integrated Article

On Modeling and Control of Continuum Robots for Minimally Invasive Medical Interventions

Author

Filipe C. Pedrosa, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Electrical and Computer Engineering

Supervisor

Patel, Rajni V.

2nd Supervisor

Jayender, Jagadeesan

Affiliation

Harvard University

Co-Supervisor

Abstract

Over the past several decades, there has been rapid advancement in technology and techniques for minimally invasive medical interventions (MIMI), particularly in minimally invasive surgery (MIS). This progress has highlighted various challenges stemming from the limitations of the current standard of care. For instance, most existing MIS systems utilize rigid laparoscopic instruments, which impose constraints on accessible workspace, intuitive control, and ergonomics. These limitations are especially restrictive for emerging techniques aiming to access internal anatomy with minimal or no incisions. To address these challenges, applications involving continuum robots have recently emerged. Leveraging flexible structures, these robots offer the capability to navigate complex, winding pathways within the body, with the potential to expand the scope of minimally invasive procedures. Motivated by two specific MIMI applications - percutaneous nephrolithotomy (PCNL) for managing large and staghorn kidney stones, and catheter-based cardiac ablation for treating arrhythmias - this thesis explores continuum robotic systems to address these clinical needs.

The thesis proposes a handheld concentric-tube robot (CTR), developed as an assistive tool for PCNL. Using an ellipsoidal approximation for the geometry of the renal calculi, it presents an image-guided, patient-specific approach to CTR design for PCNL. The method integrates an anatomically constrained, differential kinematics-based control scheme with an optimization framework to devise PCNL surgical plans and CTR designs tailored to the anatomical specificity of each patient. The surgical plans specify both the skin puncture location and an entry point at a suitable renal pyramid, thereby defining the percutaneous access tract for the procedure. The proposed method is validated through simulations in virtual environments, created from clinical data of a cohort of PCNL patients, as well as phantom-based experiments that demonstrate the efficacy of the approach and the optimality of the surgical plans.

Furthermore, this thesis addresses the modeling and control of the continuum dynamics of tendon-driven continuum robots (TDCRs), focusing on tendon-driven catheters used in cardiac ablation. The thesis introduces a Cosserat-based dynamic model of catheters that incorporates a dynamic friction model which captures tendon-sheath interactions in a geometrically exact manner. This approach accounts for complex, motion history-dependent dynamics, and models tension losses even in cases involving out-of-plane catheter curvatures. Additionally, it presents a robotic-actuated tendon-driven catheter and a real-time control framework. This framework combines a model-free, learning-based approach to model catheter dynamics using Koopman theory with model-based control techniques. Real-time control at interactive rates is demonstrated through experiments in which two optimal controllers, a linear quadratic regulator (LQR) and a robust H-infinity controller, achieve closed-loop frequencies of 250 Hz.

Summary for Lay Audience

Over the last two hundred years, medical procedures have increasingly shifted from traditional open surgeries to less invasive methods that offer patients faster recovery, reduced discomfort, and lower risk of complications. This trend, fueled by advances in medical technology, allows doctors to reach internal anatomy with minimal incisions. However, many current minimally invasive tools remain rigid and hard to control, which can lead to challenges in precision and ease of use, especially in complex procedures. To address these issues, flexible robots, known as continuum robots, offer a promising alternative. These robots can bend or change their shape, allowing for safer, more accurate navigation in challenging medical interventions. This thesis investigates the potential applications of continuum robots in two distinct minimally invasive medical interventions: the removal of large kidney stones and the treatment of irregular heart rhythms. For the kidney stone removal procedure, a novel handheld robot system was developed to assist physicians by providing personalized, image-guided robot designs and surgical plans tailored to each patient's unique anatomy. The surgical plan helps determine the optimal pathway for accessing the kidney while safeguarding the surrounding sensitive structures. The personalized robot designs enhance the volume coverage of the stone, leading to improved stone-free rates following the procedure. The effectiveness of these patient-specific methods was demonstrated through virtual simulations and experiments using phantom models that replicate the clinical setting. For the cardiac application, this research also focused on enhancing the control of tendon-driven flexible catheters during cardiac ablation, a procedure used to treat arrhythmia (irregular heartbeat). A new mathematical model was developed to better predict the complex motions of these catheters, accounting for the effects of friction on the actuation tendons. This improved model can more accurately capture the tension loss caused by frictional effects on the catheter tendons. Additionally, the thesis introduces a real-time control system that enables smooth and rapid manipulation of catheters. This system was evaluated with two controller types, both demonstrating high performance under real-time conditions. These advancements show promising potential for safer and more effective heart treatments, even in face of uncertainties in the catheter's operating conditions.

Recommended Citation

Pedrosa, Filipe C., "On Modeling and Control of Continuum Robots for Minimally Invasive Medical Interventions" (2025). Electronic Thesis and Dissertation Repository. 10711.
https://ir.lib.uwo.ca/etd/10711