High Speed Pneumatic Stepper Motor for MRI Applications.

Presented in this paper is an exploration into the efficacy of a plastic, four-cylinder piston pneumatic motor designed for driving medical instruments inside magnetic resonance imaging (MRI) systems. Because of the increasing use of MRI for diagnostic and interventional purposes and the benefits that could be realized by operating with real-time MR image guidance, there exists a significant need for MRI compliant surgical devices. Some type of actuation mechanism is necessary to drive such devices. The motor can be controlled to operate in a "step" type motion by using pneumatic valves to sequentially apply air pressure to push the piston surfaces, meaning the motor is metal-free and does not use electricity. The stepwise nature of this piston stepper motor is ideal for the accurate, controlled movements required for MRI-guided interventions. The motor was geared down by a gearbox to increase torque. Performance indices determined include output torque and achievable rotational velocity with respect to factors such as air pressure and load conditions. The stepper motor achieved speeds of approximately 2000 rpm, and maximum output torques of approximately 19 N mm. The motor represents a high speed pneumatic stepper motor design capable of actuating devices in MR environments without affecting image quality.