Lumbar injection is a minimally invasive spine procedure to relieve pain in patients with chronic low back pain. It requires accurate needle targeting at the epidural space under image guidance. Contrary to the fluoroscopy-guided manual approach, a magnetic resonance imaging (MRI)-guided robotic needle offers high soft tissue contrast and no ionising radiation exposure. However, most existing MR-safe robotic systems feature short actuation stroke, low joint stiffness, complex mechanism, and still require manual needle insertion.
This work introduces an intrinsically MR-safe robotic manipulator for the spine procedure, consisting of a two-degree-of-freedom (2-DOF) compact RCM mechanism and 1-DOF needle driver operating under bellows-based hydraulic actuation. It is equipped with hydraulically-activated locks and customised encoder for enhanced joint stiffness and closed-loop control. Communicating bellows are introduced in a closed master-follower actuation setup, minimising the risk of fluid leakage. The robotic system was capable of achieving millimetre-scale accuracy in its RCM DOFs, and negligible signal-to-noise ratio reduction during the MRI-compatibility test. The enabling technologies in this robotic system can potentially realise real-time needle manipulation and targeting under continuous MR scanning with optimal image quality.
