Design and Control of an Magnetic Resonance Compatible Precision Pneumatic Active Cannula Robot

Abstract

The versatile uses and excellent soft tissue distinction afforded by magnetic resonance imaging (MRI) has led to the development of many MRcompatible devices for MRIguided interventions. This paper presents a fully pneumatic MRcompatible robotic platform designed for neurosurgical interventions. Actuated by nonmagnetic pneumatic pistoncylinders, the robotic platform manipulates a five degreeoffreedom active cannula designed for deep brain interventions. Long lines of tubing connect the cylinders to remotely located pressure sensors and valves, and MRIcompatible optical sensors mounted on the robot provide the robot joint positions. A robust, nonlinear, modelbased controller precisely translates and rotates the robot joints, with mean steadystate errors of 0.032 mm and 0.447 deg, respectively. MRIcompatibility testing in a 3Tesla closedbore scanner has shown that the robot has no impact on the signaltonoise ratio, and that geometric distortion remains within recommended calibration limits for the scanner. These results demonstrate that pneumatic actuation is a promising solution for neurosurgical interventions that either require or can benefit from submillimeter precision. Additionally, this paper provides a detailed solution to the control problems imposed by severe nonlinearities in the pneumatic system, which has not previously been discussed in the context of MRcompatible devices.