Virtual Remote Center of Motion control for needle placement robots‡

Abstract

Surgical robots, including those with remote center of motion (RCM) mechanisms, have demonstrated utility in image-guided percutaneous needle placement procedures.However, widespread clinical application of these robots is hindered by not only complicated mechanical design but also the need for calibration and registration of the robot to the medical imager prior to each use.In response, we propose a Virtual RCM algorithm that requires only online tracking or registering the surgical tool to the imager, and a five degree-offreedom (DOF) robot comprised of three prismatic DOF and two rotational DOF.The robot can be unencoded, uncalibrated, and does not require preoperative registration.An incremental adaptive motion control cycle both guides the needle to the insertion point and orients it to align with the target.The robot executes RCM motion "virtually" without having a physically constrained fulcrum point.The proof-of-concept prototype system achieved 0.78 mm translation and 0.78 degrees rotational accuracy (within the tracker accuracy), within 17 iterative steps (0.5-1secs). Background and SignificanceRecent advances in medical imaging have inspired substantial research in robotassisted needle placement procedures.Robots have the potential to manipulate instruments more precisely to targets in the patient (using feedback from medical images) than is possible by hand.Manual needle placement typically includes the following three decoupled tasks: (1) move the needle tip to the entry point with 3-DOF Cartesian motion, (2) orient the needle by pivoting around the entry point using 2-DOF rotation, and (3) insert the needle into the body using 1-DOF translation along a straight trajectory.The challenge for robot assisted needle placement has been to reproduce this sequence of motions robotically.For a robot, the least straightforward step is needle orientation, which can be achieved using a 2-DOF design that mechanically constrains the fulcrum point at the needle tip.Taylor was the first to apply this remote center of motion (RCM) point concept in a laparoscopic robot [5].The RCM