Image-Guided Targeting and Control of Implantable Electrodes
Kratchman, Louis Beryl
Implantable electrodes are used to diagnose and treat a growing list of conditions, including deafness, chronic pain, and neurodegenerative disorders. This dissertation introduces robotic methods to make electrode implantation less invasive, safer, and easier for clinicians to perform. We focus on implantation through a narrow hole under image guidance, and contribute methods to both guide instruments along a straight insertion path and to steer electrodes that are inserted through such a hole. We present the first bone-attached robot to accurately guide instruments to the cochlea. This system removes the need to fabricate a stereotactic guide in the operating room and reduces dependence on a surgeon's skill. Results from a phantom targeting experiment show this system to be sufficiently accurate for cochlear implantation surgery. Manually adjusted stereotactic frames are used to implant deep brain stimulation (DBS) electrodes, but encumber the patient and are prone to operator errors. Smaller targeting devices are available for DBS surgery, but require offsite manufacturing or expensive image guidance systems. We introduce robotically adjusted, disposable microstereotactic frames that are rapidly adjusted, locked, and then transferred to a patient in a single visit. A phantom validation experiment shows that the targeting error of a robotically adjusted frame was below the clinically accepted threshold. Sensitive tissues can be damaged by the force of electrode implantation. Robotic insertion devices have the potential to detect and react to excessive insertion forces, but the relationship between forces and trauma is poorly understood. Presently, we rely on surgeons to judge when forces are too large, but the ability of surgeons to sense small forces when implanting electrodes has not been studied. We introduce a method to measure intraocochlear puncture forces and report the first force measurements obtained from fresh cadaveric specimens. To put these forces into a clinical perspective, we present a protocol to measure tactile thresholds in a model of CI surgery, and present the first experimental characterization of surgeons' tactile force thresholds. An electrode can be actively steered to reduce trauma and avoid obstacles. We present the first method to guide a magnet-tipped electrode along arbitrary three-dimensional trajectories using a compact, robot-manipulated magnet located external to the patient. We model rod deflections by combining Kirchhoff rod theory with permanent magnet models, and compute trajectories using a resolved-rate approach. Experiments demonstrate accurate execution of three-dimensional tip trajectories in an open-loop configuration and obstacle avoidance. This dissertation provides a complementary set of methods for improving electrode implantation. These methods could benefit both patients and clinicians who perform minimally invasive procedures.