Mahta Khoshnam

A pseudo-rigid-body 3R model for a steerable ablation catheter

Over the past few decades, catheter-based cardiac ablation has been the first surgical option for treatment of arrhythmia. In order to have an effective ablation procedure, after positioning the catheter at the desired location inside the heart chamber, a consistent tip/tissue contact should be maintained during the whole procedure. With the goal of implementing hybrid force/position control of the catheter tip during the ablation procedure, this paper studies how the catheter tip deflects when forces are applied. A pseudo-rigid-body 3R model for the catheter tip is introduced. The model performance is evaluated through extensive experiments and it is shown that the proposed model can estimate the shape of the bending section of the ablation catheter if force information is available. This model does not require extensive knowledge of the catheter internal structure. Moreover, the well-established static equations are simple to understand and solve, making this model a convenient choice for developing a control system.

Modeling of a steerable catheter based on beam theory

Catheter-based cardiac ablation is an interventional treatment for heart arrhythmias. Pull-wire steerable catheters are guided to the heart chambers through the vasculature in order to deliver energy to destroy faulty electrical pathways in the heart. The effectiveness of this treatment is dependent on the accuracy of positioning the catheter tip at the target location and also on maintaining contact with the target while the heart is beating. Therefore, it is desirable to perform hybrid force/position control of the catheter tip. We have studied the problem of modeling the distal part of a steerable catheter using beam theory and have developed and validated a static force-deflection model through extensive experiments. It is shown that the model can estimate the shape of the bending section of a catheter using force information and without requiring extensive knowledge of the catheters internal structure.

Visual servoing in medical robotics: a survey. Part I: endoscopic and direct vision imaging – techniques and applications

Intra‐operative imaging is widely used to provide visual feedback to a clinician when he/she performs a procedure. In visual servoing, surgical instruments and parts of tissue/body are tracked by processing the acquired images. This information is then used within a control loop to manoeuvre a robotic manipulator during a procedure.

Modeling and Estimation of Tip Contact Force for Steerable Ablation Catheters

Objective: The efficacy of catheter-based cardiac ablation procedures can be significantly improved if real-time information is available concerning contact forces between the catheter tip and cardiac tissue. However, the widely used ablation catheters are not equipped for force sensing. This paper proposes a technique for estimating the contact forces without direct force measurements by studying the changes in the shape of the deflectable distal section of a conventional 7-Fr catheter (henceforth called the “deflectable distal shaft,” the “deflectable shaft,” or the “shaft” of the catheter) in different loading situations. Method: First, the shaft curvature when the tip is moving in free space is studied and based on that, a kinematic model for the deflectable shaft in free space is proposed. In the next step, the shaft shape is analyzed in the case where the tip is in contact with the environment, and it is shown that the curvature of the deflectable shaft provides useful information about the loading status of the catheter and can be used to define an index for determining the range of contact forces exerted by the ablation tip. Results: Experiments with two different steerable ablation catheters show that the defined index can detect the range of applied contact forces correctly in more than 80% of the cases. Based on the proposed technique, a framework for obtaining contact force information by using the shaft curvature at a limited number of points along the deflectable shaft is constructed. Conclusion: The proposed kinematic model and the force estimation technique can be implemented together to describe the catheters behavior before contact, detect tip/tissue contact, and determine the range of contact forces. Significance: This study proves that the flexibility of the catheters distal shaft provides a means of estimating the force exerted on tissue by the ablation tip.

Model-Based Force Control of a Steerable Ablation Catheter with a Custom-Designed Strain Sensor

The increasing popularity of catheter-based ablation therapy in treating cardiac arrhythmia has motivated researchers to seek new techniques to improve the accuracy and efficiency of such procedures. After guiding the catheter through the vessels into the heart chambers, precise positioning of the catheter tip and consistent tool/tissue contact force are the two factors that greatly affect the ablation outcome. Implementing force/position control of the catheter tip will improve the efficacy of cardiac ablation procedures immensely. This paper proposes a model-based force control system to ensure a desired contact force at the distal tip, without directly measuring the force applied at the tip. In this regard, it is studied how the displacement of the proximal handle of a common 7-Fr pull-wire ablation catheter relates to the change of angle at its distal tip. The resulting mapping together with a mapping that relates the forces at the distal tip to the tip shape are used in developing a control system that ensures a desired contact force at the tip. This paper also introduces an optical strain sensor that can be used without modification in the manufacture of present day ablation catheters. This strain sensor completes the feedback loop of the control system through integration with the shape to force model. Performance of the control system is evaluated experimentally and the results suggest that model-based control of steerable catheters is feasible for catheter ablation. The proposed control system can be employed on a conventional ablation catheter following a fairly simple calibration step.

Robotics-assisted catheter manipulation for improving cardiac ablation efficiency

The quality of contact between the catheter tip and cardiac tissue has been identified as an important factor in the efficacy of the catheter-based cardiac ablation procedures. However, maintaining a constant tip/tissue contact force during the procedure is difficult due to cardiac and respiratory motions. Robotic manipulation of the catheter has the potential to overcome this difficulty and decrease the range of variations in the contact force during the ablation procedure. This paper investigates the possibility of performing motion compensation for conventional steerable ablation catheters using a robotic manipulator. The behavior of such catheters is analyzed in free space as well as in contact with static and moving targets and the limitations in the actuation mechanism are identified. Based on this analysis, a technique for synchronizing the motion of the catheter tip with cardiac motion is proposed. The suggested control system estimates the frequency of the moving target and reshapes the input trajectory accordingly. The performance of the resulting system is evaluated experimentally. The results show that in the experimental setting, the proposed technique reduces the variations in the contact force and noticeably improves the quality of tip/tissue contact.

A robotics-assisted catheter manipulation system for cardiac ablation with real-time force estimation

Lack of dexterous control over the position of a catheters distal tip and not having any feedback from the quality of tip - tissue contact are among the factors that make the conventional catheter-based method of performing cardiac ablation very challenging. To resolve these issues, in this paper, we present a robotic catheter manipulation system that accommodates a conventional ablation catheter, places the ablation tip at the desired target and reports the forces that the tip exerts on the environment in real-time. In this system, the manual proximal handle is replaced with a mechanism that is capable of measuring the tension force along the pull-wire while actuating it to flex the distal shaft of the catheter. The placement of force/pressure sensors at the distal end of the catheter is avoided by developing a model-based force estimation technique using the measured tension force and information on the position and orientation of the distal tip. The developed system is further enhanced with an interface to assist the user in placing the catheter tip at the desired location while providing him/her with a real-time measure of the contact force. Extensive experiments show that using the proposed robotic system, the catheter tip is positioned within ±1 mm of the designated target and contact forces are reported in real-time with an accuracy of 3 gf.

Visual servoing in medical robotics: a survey. Part II: tomographic imaging modalities--techniques and applications.

Intraoperative application of tomographic imaging techniques provides a means of visual servoing for objects beneath the surface of organs.

Estimating contact force for steerable ablation catheters based on shape analysis

Cardiac ablation using flexible catheters is a common interventional procedure for treating cardiac arrhythmia. This procedure is performed under image guidance and the contact force between the ablation tip and the heart tissue is one of the factors that greatly impacts the efficacy of the ablation procedure. This paper investigates the feasibility of estimating the force that the catheter tip exerts on the heart tissue by monitoring the changes in the shape of the deflectable distal shaft of the catheter (henceforth called the “deflectable shaft” or the “shaft” of the catheter). It is shown that variations in the shaft curvature provide information about how much force the catheter tip is exerting at its point of contact. Consequently, an index is defined for determining the range of contact forces based on the shaft curvature. Experimental results show that the defined index can correctly detect the range of applied contact forces in more than 80% of the cases. This study proves that the flexibility of the deflectable shaft provides a means of estimating contact forces exerted by the catheter tip.

Robotics-Assisted Control of Steerable Ablation Catheters Based on the Analysis of Tendon-Sheath Transmission Mechanisms

Catheter-based cardiac ablation is a minimally invasive intervention for treating arrhythmia. In this procedure, access to target cardiac tissue in the atrium is provided by steering long flexible catheters through the vasculature. Using the proximal handle, the distal shaft of the ablation catheter is flexed to adjust the orientation of the ablation tip with respect to cardiac tissue. Considering the diameter of an ablation catheter and the necessity for remote actuation of the distal shaft in this case, a pull-wire mechanism is used to translate the linear displacement of the proximal handle to the bending of the distal shaft. In this paper, we study the transmission characteristics of a unidirectional steerable ablation catheter as a tendon-driven mechanism. We then propose a model that estimates the orientation of the distal shaft using only proximal measurements. Based on this model, a control system is designed to flex the distal shaft to reach a desired angle or to follow a defined trajectory in free space. In the case that the catheter tip is in contact with the environment, we show that the proposed controller can compensate for tissue motion by flexing the distal shaft accordingly, and thus, consistent tip–tissue contact is achieved. Extensive simulation studies and experimental implementation demonstrate the effectiveness of the proposed approach. Using the developed control system, the error in achieving the desired angle in free space is less than 2