Modeling, force estimation and control of steerable catheters for robot-assisted intra-cardiac navigation

Intra-cardiac catheterization is an effective procedure for diagnosis and treatment of many cardiac disorders such as arrhythmia. The objective of the catheter manipulation is to accurately position the catheter tip at the target tissue on the endocardium and provide a stable contact force for a specific duration to the region of interest. However, this is a challenging task due to the high flexibility of the catheter, ineffective visualization and dynamic environment of the heart. Additionally, the catheter-tissue interaction force, that the procedure outcome highly depends on, is not known to the interventionalist during the catheterization. This thesis deals with improving the safety and effectiveness of the catheterization by making contributions to two main areas; catheter contact force estimation and automatic force/position control of a robotic catheter system. First, a quasi-static model of the planar catheter that predicts the catheter pose for the given actuation variables and external forces in the plane of catheter motion, is proposed. In the next step, the computational efficiency of the proposed model is utilized to develop an online approach for the estimation of the external force at the tip of a catheter based on the pose measurement. The proposed force estimation approach is also extended to 3D by developing an efficient model of the catheter that is derived by coupling the classical Cosserat rod model with a new model of the pull-wire actuation. Experiments performed using electromagnetic sensors verify the feasibility of the proposed schemes in medical applications. In the control area, a position control scheme for a robotic assisted manipulation system is proposed, using the experimentally obtained inverse kinematics that compensates for the non-smooth dynamics of the distal shaft bending mechanism. Compensation of the backlash behavior of the catheter due to its interaction with the surrounding veins is also incorporated in the control scheme. The proposed position controller is then adopted as the internal loop of a hybrid position/force controller that positions the catheter tip to the target tissue and simultaneously, regulates the contact force to a desired value. The viability of the proposed controllers is then verified through simulations and experiments.