Pneumatic Piston Stepper Motor: An Enabler for MRI-Guided Robotic Interventions

Magnetic resonance (MR) imaging (MRI) has become the preferred method for medical diagnosis due to high resolution images and lack of ionizing radiation. Recently, the potential for using MRI to obtain real-time image feedback for targeted therapeutic procedures such as targeted biopsies and injections has been explored [1]. Some devices designed for intra-MRI use exist and more such devices are currently being developed and researched. Procedures often require precise positional targeting, such as injections and biopsies, and an MRI safe controlled-motion stepper motor is an ideal choice for actuating these mechanical devices. Some such drivers have been developed, but for various reasons, none are considered to be the standard for MRI use at this time. Therefore, a new design combining certain aspects of previous motors has been developed, making use of newer three-dimensional (3D) printers with extreme accuracy. Presented is a small, low-cost plastic four-cylinder piston stepper motor which is actuated by pressurized air. Connected to a plastic gearbox, this motor is capable of driving a rotational shaft at torques of up to 20 N·mm by increments of 3.6 degrees.