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

The versatile uses and excellent soft tissue distinction afforded by magnetic resonance imaging (MRI) has led to the development of many MR-compatible devices for MRI-guided interventions. This paper presents a fully pneumatic MR-compatible robotic platform designed for neurosurgical interventions. Actuated by nonmagnetic pneumatic piston-cylinders, the robotic platform manipulates a five degree-of-freedom active cannula designed for deep brain interventions. Long lines of tubing connect the cylinders to remotely located pressure sensors and valves, and MRI-compatible optical sensors mounted on the robot provide the robot joint positions. A robust, nonlinear, model-based controller precisely translates and rotates the robot joints, with mean steady-state errors of 0.032 mm and 0.447 deg, respectively. MRI-compatibility testing in a 3-Tesla closed-bore scanner has shown that the robot has no impact on the signal-to-noise 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 MR-compatible devices.