An MR-Safe Robotic Manipulator With Hydraulic Bellows Actuators for Spine Procedures

Lumbar injection is a minimally invasive spinal procedure that requires accurate needle targeting in the spinal region under image guidance. Contrary to X-ray imaging commonly used for this procedure, magnetic resonance imaging (MRI) offers high soft tissue contrast and no ionizing radiation exposure. However, most existing magnetic resonance (MR)-safe robotic needle manipulators feature short stroke, low joint stiffness, and complex mechanism. This work introduces an intrinsically MR-safe robotic needle for the spine procedure, consisting of a 2-degree-of-freedom (DOF) compact remote center of motion (RCM) mechanism and 1-DOF needle driver operating under bellows-based hydraulic actuation. It is equipped with hydraulically activated locks and customized encoders for enhanced joint stiffness and closed-loop control. Communicating bellows are introduced in the teleoperation setup, minimizing the risk of fluid leakage. A geometry-based static model was developed and verified for the communicating bellows actuation system. The robotic system was shown to achieve subdegree and submillimeter motion accuracy in its RCM DOFs, and negligible signal-to-noise ratio reduction during the MR imaging quality test. This is to the authors' knowledge, the first robotic manipulator with both motorized RCM and needle translation using MR-safe hydraulic bellows actuators, potentially enabling real-time needle orientation and placement control under continuous MR scanning with optimal image quality.