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Prof. Rajni Patel, University of Western Ontario
Rajni V. Patel (M’76–SM’80–F’92) received the Ph.D. degree in Electrical Engineering from the University of Cambridge, England, in 1973 and currently holds the position of Distinguished University Professor and Tier-1 Canada Research Chair in the Department of Electrical and Computer Engineering with a cross appointment in the Department of Surgery in the Schulich School Medicine and Dentistry at the University of Western Ontario, Canada.  Dr. Patel also serves as Director of Engineering for Canadian Surgical Technologies & Advanced Robotics (CSTAR).  He is a Life Fellow of the IEEE, and a Fellow of the ASME, the Royal Society of Canada and the Canadian Academy of Engineering. He has served on the editorial boards of the IEEE Transactions on Robotics, the IEEE/ASME Transactions on Mechatronics, the IEEE Transactions on Automatic Control, and Automatica, and is currently a member of the Editorial Board of the International Journal of Medical Robotics and Computer Assisted Surgery. 

Control of Tip Contact Force for Steerable Ablation Catheters
Catheter-based cardiac ablation is a well-accepted treatment for atrial fibrillation, a common type of cardiac arrhythmia [1]. During this procedure, a steerable ablation catheter is guided through the vasculature to the left atrium. The catheter is then used to ablate some parts of cardiac tissue to restore normal heart rhythm. An important factor that affects the efficacy of the ablation procedure is the contact force between the catheter tip and cardiac tissue [2] and it is desired to maintain a constant contact force in spite of cardiac motion [3]. However, in the conventional method of performing cardiac ablation, force information is not available and alternate techniques for estimating the contact force need to be developed. 
In the context of continuum robots, estimating contact forces using information from sources other than force sensors has been a topic of recent interest [4-11]. This talk will focus on the design of a robotics-assisted catheter manipulation system with contact force control for use in cardiac ablation procedures. As a basic step in this regard, the behavior of current ablation catheters in different scenarios will be discussed to better understand their features and limitations. In the static case, it will be shown that it is possible to determine the tip/tissue contact force from the catheter shape without installing a force sensor on the catheter. During cardiac ablation, the catheter tip is in contact with a relatively fast-moving environment (cardiac tissue). For maintaining a constant contact force, the catheter tip should be actuated at frequencies close to those of cardiac motion. Robotic manipulation of the catheter has the potential to provide such motion. The talk will present some recent results on different properties of ablation catheters, e.g., how the catheter tip deflects when the catheter handle is actuated and when the catheter comes in contact with static as well as moving environments. Techniques for controlling the contact force and their limitations will be discussed. Based on these results, a modified actuation technique as well as suggestions for improved catheter design will be presented.
 

Relevant publications

[1] A. Verma, "The techniques for catheter ablation of paroxysmal and persistent atrial fibrillation: a systematic review," vol. 26, no. 1, pp. 17-24, Jan 2011.

[2] V.Y. Reddy et al., "The relationship between contact force and clinical outcome during radiofrequency catheter ablation of atrial fibrillation in the TOCCATA study ," Heart Rhythm, vol. 9, no. 11, pp. 1789-1795, Nov. 2012.

[3] D.C. Shah et al., "Area under the real-time contact force curve (forcetime integral) predicts radiofrequency lesion size in an in vitro contractile model," Journal of Cardiovascular Electrophysiology, vol. 21, no. 9, pp. 1038-1043, Sep 2010.

[4] K. Xu and N. Simaan, "An investigation of the intrinsic force sensing capabilities of continuum robots," IEEE Transactions on Robotics, vol. 24, no. 3, pp. 576-587, June 2008.

[5] K. Xu and N. Simaan, "Intrinsic wrench estimation and its performance index for multisegment continuum robots," IEEE Transactions on Robotics, vol. 26, no. 3, pp. 555-561, June 2010.

[6] A. Bajo and N. Simaan, "Finding lost wrenches: Using continuum robots for contact detection and estimation of contact location," in IEEE International Conference on Robotics and Automation (ICRA), 2010, pp. 3666-3673.

[7] D. Rucker and R. Webster, "“Deflection-based force sensing for continuum robots: A probabilistic approach," in IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2011, pp. 3764-3769.

[8] D.C. Rucker and R.J. Webster, "Statics and dynamics of continuum robots with general tendon routing and external loading," IEEE Transactions on Robotics, vol. 27, no. 6, pp. 1033-1044, Dec. 2011.

[9] I.A. Gravagne and I.D. Walker, "Manipulability, force, and compliance analysis for planar continuum manipulators," IEEE Transactions on Robotics and Automation, vol. 18, no. 3, pp. 263-273, June 2002.

[10] M. Khoshnam, M. Azizian, and R.V. Patel, "Modeling of a steerable catheter based on beam theory," in IEEE International Conference on Robotics and Automation (ICRA), 2012, pp. 4681-4686.

[11] M. Khoshnam and R.V. Patel, "A pseudo-rigid-body 3R model for a steerable ablation catheter," in IEEE International Conference on Robotics and Automation (ICRA), 2013, pp. 4412-4417.

[12] M. Khoshnam, A. Yurkewich, and R.V. Patel, "Model-based force control of a steerable ablation catheter with a custom-designed strain sensor," in IEEE International Conference on Robotics and Automation (ICRA), 2013, pp. 4464-4469.