Gabrijel Smoljkic

Catheter navigation based on probabilistic fusion of electromagnetic tracking and physically-based simulation

Minimally invasive endovascular procedures including robotically assisted intervention require effective intraoperative guidance. This is mainly achieved through intraoperative imaging such as fluoroscopy. Concerns over excessive x-ray radiation and nephrotoxicity due to repeated injection of contrast agents have motivated the development of effective catheter navigation schemes based on limited imaging data. This paper presents a catheter navigation technique based on probabilistic fusion of in situ real-time electromagnetic tracking with physically-based simulation of the mechanical characteristics of the catheter. A catheter with multiple electromagnetic sensors placed along its length has been developed. The sensor data and the catheter insertion-length are used as the boundary condition for determining the shape and position of the catheter within the vasculature. A probabilistic framework based on a Kalman Filter is used to combine the information from the catheter motion algorithm and the electromagnetic tracking data. This provides continuous visualization of the catheter within the lumen without the need of continuous fluoroscopy and contrast injection. The proposed approach has been validated with detailed in vitro experiments demonstrating the potential clinical application of the technique.

Constraint-Based Interaction Control of Robots Featuring Large Compliance and Deformation

This paper introduces a framework for constraint-based force/position control of robots that exhibit large nonlinear structural compliance and that undergo large deformations. Controller synthesis follows hereto the principles of the Task Frame and instantaneous Task Specification using Constraints (iTaSC) formalisms. iTaSC is found particularly suitable due to its ability to express and combine control tasks in a natural way. Control tasks can be formulated as combinations of target positions, velocities, or forces expressed in an arbitrary number and type of coordinate frames. The proposed framework is applied to a mixed mechatronic system composed of a traditional rigid-link robot whose end-effector is a continuum (flexible) link. A selection of different position/force control tasks is prepared to demonstrate the validity and general nature of the proposed framework.

Compliance Computation for Continuum Types of Robots

This paper presents a mathematical formulation for calculation of the compliance of continuum type of robots. The mathematical model of the continuum robot is built following the Cosserat rod theory and focuses on a single section Cosserat rod under arbitrary loading. The compliance of the robot is described as a set of ordinary differential equations with split boundary conditions. This new set of compliance equations is directly coupled to the solution of the forward kinematics of the robot. After solving the forward kinematics problem, these solutions can be directly used to compute the compliance. A particular class of continuum robots in which the compliance of the robot can be formulated as an initial value problem and solved in a single numerical integration is discussed. The paper provides experimental validation of the proposed method.

Position control of robotic catheters inside the vasculature based on a predictive minimum energy model

Accurate and precise control of catheters inside a vasculature is a difficult yet important task. Current manual approaches require significant surgical skill. Over the years, surgeons build up a sort of mental kinematic map telling them how to handle the catheter in order to steer the catheter tip safely through the vessel system. The input-output behaviour of the catheter is complex and depends heavily on its configuration within and contacts with the vasculature. This paper introduces an alternative approach to control robotic catheters. The input-output behaviour or so-called differential kinematics are derived from a patient-specific vasculature model, following a minimum-energy argumentation. The validity of the proposed approach is demonstrated experimentally. Whereas the performance of model-based approaches is obviously greatly influenced by the correctness of estimated parameters, within this work we show experimentally how reasonable performance can already be achieved within the setup that was constructed. We expect that there is still ample room for improvement by, e.g., putting more sophisticated identification, modeling and collision detection schemes into place.

Force Control of a Rigid Robot with a Flexible Link

This paper introduces a conceptual design of a hybrid mechatronic system consisting of a rigid robotic arm and a flexible link. The hybrid system represents an intermediate step towards a new type of instruments to be employed in the field of robotic surgery. These instruments are characterized by high distal structural flexibility allowing for safer interaction with the tissue. This paper shows that despite of the flexibility it is possible to accurately control the interaction forces between the robot and the soft and delicate tissue. To this end, a force control method is suggested, featuring quasi-static system model that is resolved in real-time inside the control law. The paper describes the overall system architecture, explains the basic concept behind the force control law and includes experimental validation of the force control of the hybrid mechatronic system. Conclusions are drawn and some indications for further work are formulated.

Cognitive Autonomous Catheters Operating in Dynamic Environments

Advances in miniaturized surgical instrumentation are key to less demanding and safer medical interventions. In cardiovascular procedures interventionalists turn towards catheter-based interventions, treating patients considered unfit for more invasive approaches. A positive outcome is not guaranteed. The risk for calcium dislodgement, tissue damage or even vessel rupture cannot be eliminated when instruments are maneuvered through fragile and diseased vessels. This paper reports on the progress made in terms of catheter design, vessel reconstruction, catheter shape modeling, surgical skill analysis, decision making and control. These efforts are geared towards the development of the necessary technology to autonomously steer catheters through the vasculature, a target of the EU-funded project Cognitive AutonomouS CAtheters operating in Dynamic Environments (CASCADE). Whereas autonomous placement of an aortic valve implant forms the ultimate and concrete goal, the technology of individual building blocks to reach such ambitious goal is expected to be much sooner impacting and assisting interventionalists in their daily clinical practice.