Toward a Meso-Scale SMA-Actuated MRI-Compatible Neurosurgical Robot

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Abstract
Brain tumors are the most feared complications of cancer. Their treatment is challenging because of the lack of good imaging modality and the inability to remove the complete tumor. Facilitating tumor removal by accessing regions outside the “line of sight” will require a highly dexterous and magnetic resonance imaging (MRI)-compatible robot. We present our work toward the development of an MRI-compatible neurosurgical robot. We used two antagonistic shape memory alloy (SMA) wires as actuators for each joint. Because of the size limitation of the device, we rely on temperature feedback to control the joint motion of the robot. We have developed a theoretical model based on Tanaka's model to characterize the joint motion with the change in SMA wire temperature. The results demonstrated that the SMA wire temperature can be used reliably to predict the motion of the robot. We then used a pulse-width modulation (PWM) scheme and switching circuit to control the temperature of multiple SMA wires. Experimental results showed that we can actuate the robot reliably and observe joint motion in a gelatin medium. Magnetic resonance (MR) images also showed that the robot is fully MRI-compatible and creates no significant image distortion.

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