MRI-compatible manipulator with remote-center-of-motion control

Purpose: To develop and assess a needle-guiding manipulator for MRI-guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site. Materials and Methods: The manipulator consists of a three-degrees-of-freedom (DOF) base stage and passive needle holder with unconstrained two-DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage. Results: The manipulator assists in searching for an optimal needle insertion path which is a complex and time-consuming task in MRI-guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However. the alignment time with the virtual RCM was not shorter when imaging time for. planning were considered. Conclusion: The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open-configuration MRI.