Taoming Liu

Three dimensional modeling of an MRI actuated steerable catheter system

This paper presents the three dimensional kinematic modeling of a novel steerable robotic ablation catheter system. The catheter, embedded with a set of current-carrying micro-coils, is actuated by the magnetic forces generated by the magnetic field of the MRI scanner. This paper develops a 3D model of the MRI actuated steerable catheter system by using finite differences approach. For each finite segment, a quasi-static torque-deflection equilibrium equation is calculated using beam theory. By using the deflection displacements and torsion angles, the kinematic modeling of the catheter system is derived. The proposed models are evaluated by comparing the simulation results of the proposed model with the experimental results of a proof-of-concept prototype.

Modeling and Validation of the Three-Dimensional Deflection of an MRI-Compatible Magnetically Actuated Steerable Catheter

Objective: This paper presents the 3-D kinematic modeling of a novel steerable robotic ablation catheter system. The catheter, embedded with a set of current-carrying microcoils, is actuated by the magnetic forces generated by the magnetic field of the magnetic resonance imaging (MRI) scanner. Methods: This paper develops a 3-D model of the MRI-actuated steerable catheter system by using finite differences approach. For each finite segment, a quasi-static torque-deflection equilibrium equation is calculated using beam theory. By using the deflection displacements and torsion angles, the kinematic model of the catheter system is derived. Results: The proposed models are validated by comparing the simulation results of the proposed model with the experimental results of a hardware prototype of the catheter design. The maximum tip deflection error is 4.70 mm and the maximum root-mean-square error of the shape estimation is 3.48 mm. Conclusion: The results demonstrate that the proposed model can successfully estimate the deflection motion of the catheter. Significance: The presented 3-D deflection model of the magnetically controlled catheter design paves the way to efficient control of the robotic catheter for the treatment of atrial fibrillation.

Towards active tracking of beating heart motion in the presence of arrhythmia for robotic assisted beating heart surgery.

In robotic assisted beating heart surgery, the control architecture for heart motion tracking has stringent requirements in terms of bandwidth of the motion that needs to be tracked. In order to achieve sufficient tracking accuracy, feed-forward control algorithms, which rely on estimations of upcoming heart motion, have been proposed in the literature. However, performance of these feed-forward motion control algorithms under heart rhythm variations is an important concern. In their past work, the authors have demonstrated the effectiveness of a receding horizon model predictive control-based algorithm, which used generalized adaptive predictors, under constant and slowly varying heart rate conditions. This paper extends these studies to the case when the heart motion statistics change abruptly and significantly, such as during arrhythmias. A feasibility study is carried out to assess the motion tracking capabilities of the adaptive algorithms in the occurrence of arrhythmia during beating heart surgery. Specifically, the tracking performance of the algorithms is evaluated on prerecorded motion data, which is collected in vivo and includes heart rhythm irregularities. The algorithms are tested using both simulations and bench experiments on a three degree-of-freedom robotic test bed. They are also compared with a position-plus-derivative controller as well as a receding horizon model predictive controller that employs an extended Kalman filter algorithm for predicting future heart motion.

Optimal needle grasp selection for automatic execution of suturing tasks in robotic minimally invasive surgery

This paper presents algorithms for optimal selection of needle grasp, for autonomous robotic execution of the minimally invasive surgical suturing task. In order to minimize the tissue trauma during the suturing motion, the best practices of needle path planning that are used by surgeons are applied for autonomous robotic surgical suturing tasks. Once an optimal needle trajectory in a well-defined suturing scenario is chosen, another critical issue for suturing is the choice of needle grasp for the robotic system. Inappropriate needle grasp increases operating time requiring multiple regrasps to complete the desired task. The proposed methods use manipulability, dexterity and torque metrics for needle grasp selection. A simulation demonstrates the proposed methods and recommends a variety of grasps. Then a realistic demonstration compares the performances of the manipulator using different grasps.

Catadioptric stereo tracking for three dimensional shape measurement of MRI guided catheters

The recent introduction of Magnetic Resonance Imaging (MRI)-actuated steerable catheters lays the ground work for increasing the efficacy of cardiac catheter procedures. The MRI, while capable of imaging the catheter for tracking and control, does not fulfill all of the needs required to identify and develop a complete catheter model. Specifially, the frequency response of the catheter must be identified to ensure stable control of the catheter system. This requires a higher frequency imaging than the MRI can achieve. This work uses a catadioptric stereo camera system consisting of a mirror and a single camera in order to track a MRI actuated catheter inside a MRI machine. The catadioptric system works in parallel to the MRI and is capable of recording the catheter at 60 fps for post processing. The accuracy of the catadioptric system is verified in imaging conditions that would be found inside the MRI. The stereo camera is then used to track a catheter as it is actuated inside the MRI.

Design of a magnetic resonance imaging guided magnetically actuated steerable catheter

This paper presents design optimization of a magnetic resonance imaging (MRI) actuated steerable catheter for atrial fibrillation ablation in the left atrium. The catheter prototype, built over polymer tubing, is embedded with current-carrying electromagnetic coils. The prototype can be deflected to a desired location by controlling the currents passing through the coils. The design objective is to develop a prototype that can successfully accomplish the ablation task. To complete the tasks, the catheter needs to be capable of reaching a set of desired targets selected by a physician on the chamber and keeping a stable contact with the chamber surface. The design process is based on the maximization of the steering performance of the catheter by evaluating its workspace in free space. The selected design is validated by performing a simulation of an ablation intervention on a virtual model of the left atrium with a real atrium geometry. This validation shows that the prototype can reach every target required by the ablation intervention and provide an appropriate contact force against the chamber.

Experimental validation of the pseudo-rigid-body model of the MRI-actuated catheter

An MRI-actuated catheter is a novel robotic catheter system that utilizes the MRI for both remote steering and visualization for catheter ablation of atrial fibrillation. Planning and control of the catheter requires a sufficiently fast yet accurate model of the catheter. The pseudo-rigid-body (PRB) model offers a reasonable trade-off between speed and accuracy by approximating the continuum catheter as rigid links connected by flexible joints, thus reducing the infinite degrees of freedom of the continuum mechanism to a finite one. In this paper, a PRB model of the MRI-actuated catheter is validated experimentally by comparing the deflections of the PRB model with the deflections of the catheter prototype.

Iterative Jacobian-Based Inverse Kinematics and Open-Loop Control of an MRI-Guided Magnetically Actuated Steerable Catheter System

This paper presents an iterative Jacobian-based inverse kinematics method for a magnetic resonance imaging (MRI) guided magnetically actuated steerable intravascular catheter system. The catheter is directly actuated by magnetic torques generated on a set of current-carrying microcoils embedded on the catheter tip by the magnetic field of the MRI scanner. The Jacobian matrix relating changes of the currents through the coils to changes of the tip position is derived using a three-dimensional kinematic model of the catheter deflection. The inverse kinematics is numerically computed by iteratively applying the inverse of the Jacobian matrix. The damped least square method is implemented to avoid numerical instability issues that exist during the computation of the inverse of the Jacobian matrix. The performance of the proposed inverse kinematics approach is validated using a prototype of the robotic catheter by comparing the actual trajectories of the catheter tip obtained via open-loop control with the desired trajectories. The results of reproducibility and accuracy evaluations demonstrate that the proposed Jacobian-based inverse kinematics method can be used to actuate the catheter in an open loop to successfully perform complex ablation trajectories required in atrial fibrillation ablation procedures. This study paves the way for effective and accurate closed-loop control of the robotic catheter with real-time feedback from MRI guidance in subsequent research.

Parameter optimization of pseudo-rigid-body models of MRI-actuated catheters

Simulation and control of a system containing compliant mechanisms such as cardiac catheters often incur high computational costs. One way to reduce the costs is to approximate the mechanisms with Pseudo-Rigid-Body Models (PRBMs). A PRBM generally consists of rigid links connected by spring-loaded revolute joints. The lengths of the rigid links and the stiffnesses of the springs are usually chosen to minimize the tip deflection differences between the PRBM and the compliant mechanism. In most applications, only the relationship between end load and tip deflection is considered. This is obviously not applicable for MRI-actuated catheters which is actuated by the coils attached to the body. This paper generalizes PRBM parameter optimization to include loading and reference points along the body.Simulation and control of a system containing compliant mechanisms such as cardiac catheters often incur high computational costs. One way to reduce the costs is to approximate the mechanisms with Pseudo-Rigid-Body Models (PRBMs). A PRBM generally consists of rigid links connected by spring-loaded revolute joints. The lengths of the rigid links and the stiffnesses of the springs are usually chosen to minimize the tip deflection differences between the PRBM and the compliant mechanism. In most applications, only the relationship between end load and tip deflection is considered. This is obviously not applicable for MRI-actuated catheters which is actuated by the coils attached to the body. This paper generalizes PRBM parameter optimization to include loading and reference points along the body.