Haptics enabled robot-assisted active catheter insertion

Abstract

This research project is concerned with developing robotic technology and control strategies that are capable of inserting and manipulating a flexible catheter 1-3 mm in diameter and up to 100 cm in length inside an artery for performing angioplasty. The clinician has no feedback on the force applied by the tip of the catheter on the walls of the blood vessel. Excessive pressure can rupture the blood vessel or dislodge plaque. Nearly 7% of carotid stenting procedures lead to death or ischaemic stroke within 30 days mainly due to dislodging of plaque and intra cerebral bleeding. The healthcare providers who perform the procedure using X-ray fluoroscopy over a prolonged period of time may have dangerous long-term exposure to X-ray radiation, which may lead to radiation burns and cancer. In this thesis, we have micromachined a catheter with Shape Memory Alloy (SMA) actuators to provide bending at the tip of the catheter to guide it through the complex vasculature in the body. There are two major problems involved in using SMA actuators - (1), They have very low machinability; (2), they demonstrate a nonlinear hysteretic behavior, as a result of which their control is imprecise and difficult. We have developed microfabrication techniques involving laser cutting and micro-spot welding to fabricate the active catheter. In order to accurately control the strain in the SMA actuators, we have developed a model based on heat transfer dynamics, Fermi-Dirac statistics and the constitutive equation. Using this model, we have designed and implemented robust (LQR optimization based and H∞ ) control algorithms to precisely control the strain in the SMA actuators. These control schemes ensure accurate tracking of the reference in the presence of perturbations and in uncertain environments, as encountered in the human vasculature. The active catheter is also instrumented with a miniaturized 3-DOF sensor to measure the force acting on the tip of the catheter. Based on the H∞ robust controller, we have developed a bilateral teleoperation scheme to remotely control the orientation of the active catheter while reflecting the forces acting on the catheter tip to the clinician. Delays are introduced in the control loop by the temperature dynamics of the SMA actuators and the nonlinear response of the actuator to input current. We have developed a wave variables based teleoperation algorithm to perform stable and transparent bilateral teleoperation of an active catheter. In addition, we have also designed and developed force control algorithms on the active catheter such that the catheter can autonomously maintain a certain desired force of contact or regulate the force acting on the catheter tip (compliant force control). This can be particularly useful in guiding the catheter smoothly within the body without any damage to the blood vessel by ensuring that the force acting on the catheter tip is minimized. In order to prevent the clinician from being exposed to harmful X-rays, we have designed and implemented force/position control (Augmented Hybrid Impedance Control) algorithms and tested them on a Mitsubishi 7-DOF robot to perform remote robot-assisted catheter insertion. The AHIC scheme applied to the robot controls the force of insertion and prevents buckling of the catheter by regulating the moments in the orthogonal directions, while controlling the position of the end-effector in Cartesian space. In this thesis, we have shown that it is possible to perform catheter insertion far more accurately than manually possible due to the precise control over the force of insertion. In addition, this approach also prevents exposure of the clinician to harmful X-ray radiation and provides him/her with an ergonomic position from which to perform robot-assisted catheter insertion. Novel image processing algorithms have been developed to track the catheter tip in real time as the catheter advances within the vasculature. We have developed a completel