A Testbed for Multi-lumen Steerable Needle Experiments

Steerable needles offer the potential to “turn corners” during insertion, thereby avoiding obstacles, reducing tip placement error, and enabling less-invasive access to challenging anatomical locations. In this paper we describe an experimental testbed designed to facilitate experiments with several popular steering mechanisms. One such mechanism makes use of asymmetric forces generated by a bevel tip for actuating steerable needles, and another uses multiple concentric precurved tubes that can change needle shaft shape by rotating within one another and extending telescopically. The experimental testbed consists of a new robotic actuation unit for controlling axial rotation and linear translation of multiple tubes. It also includes stereo optical cameras and a magnetic tracking system for feedback of needle shape and tip location. The setup can be used in future work for model validation and closed-loop feedback control of steerable needles and cannulae. INTRODUCTION Surgical needles provide one of the least invasive methods of accessing sites within the human body. They are useful for a wide variety of diagnostic and interventional procedures including biopsy [1], neurosurgery [2], regional anesthesia and brachytherapy [3], among many others. In needle-based procedures, clinical outcomes are closely related to the accuracy of needle tip placement to the desired site. However, precise targeting is challenging because of needle deformation during insertion, registration error, and tissue deformation, among other factors. These can cause the needle to miss the desired target, and such trajectory errors can often be visualized using intraoperative medical images. This has motivated the recent development of a number of needle steering strategies to enable control of needle trajectory and shape within tissue. One popular mechanism for steering needles is to harness asymmetric tip forces (e.g., a bevel tip – see Figure 1) to controllably deflect the needle. Another popular method of steering needles (or more precisely, changing shaft shape) is to use a needle composed of multiple precurved flexible concentric tubes (see Figure 2). Like a bevel tipped needle, these active cannulas composed of concentric tubes are actuated by the axial translation and rotation of the proximal end of each component tube. In both tip-steered and concentric tube needles, an experimental testbed is needed to verify kinematic modeling and closed-loop control results. In this paper we describe the most recent experimental testbed we have developed to enable experiments with both tip-steered needles and concentric tube active cannulas and combinations of the two. Our testbed consists of a novel robotic actuation unit for controlling the axial rotation and linear translation of several tubes, the innermost of which may be a bevel-steered needle if desired. Feedback in our system comes from stereo optical cameras and a magnetic tracker, enabling experiments in both transparent