Towards the development of a SMA-actuated MRI-compatible tendon-driven neurosurgical robot

In this paper, we present the design and development of a magnetic resonance imaging (MRI)-compatible tendon-driven robot to overcome the limitations of our previous minimally invasive neurosurgical intracranaial robot (MINIR). In this prototype, the robot is made of plastic and the MRI-compatible shape memory alloy (SMA) actuators are placed away from the robot. The robot has four revolute joints which are placed orthogonally to have out-of-plane motion capability. Each joint is connected to a pair of antagonistic SMA spring actuators through the tendon-sheath mechanism. Each SMA spring actuator can be controlled independently to actuate the corresponding joint. A theoretical model and experimental setup have been developed to evaluate the recovery force of the SMA spring at different displacement and temperatures. The experimental results closely match the theoretical model and it shows significant promise for future development in this area. A series of MRI compatibility tests have also been performed to evaluate the MRI compatibility of the device and to assess the degradation in image quality, if any, during actuation. The experimental results clearly demonstrate that the robot is MRI-compatible and it creates no significant distortion in the MR images during actuation.