CRANE: A Redundant, Multi-Degree-of-Freedom Computed Tomography Robot for Heightened Needle Dexterity within a Medical Imaging Bore

TL;DR

CRANE addresses the challenge of accurate, radiation-conscious CT-guided needle placement by enabling automated in-bore manipulation with a redundant, cable-driven robot. The approach combines a high-dexterity end-effector with remote actuation, a novel SMA-based needle gripper, and a unified planning/control framework that automatically setups the device and plans dexterous trajectories in image space. Validation includes simulated dexterity studies and physical bench-top and phantom experiments demonstrating high precision (closed-loop mean errors of approximately $0.27\ \mathrm{mm}$ and $0.71^{\circ}$ on RCM trajectories) and robust needle gripping. The work advances automated intra-bore robotics for interventional radiology, supporting broader clinical workflows and patient morphologies while highlighting remaining challenges for clinical translation.

Abstract

Computed Tomography (CT) image guidance enables accurate and safe minimally invasive treatment of diseases, including cancer and chronic pain, with needle-like tools via a percutaneous approach. The physician incrementally inserts and adjusts the needle with intermediate images due to the accuracy limitation of free-hand adjustment and patient physiological motion. Scanning frequency is limited to minimize ionizing radiation exposure for the patient and physician. Robots can provide high positional accuracy and compensate for physiological motion with fewer scans. To accomplish this, the robots must operate within the confined imaging bore while retaining sufficient dexterity to insert and manipulate the needle. This paper presents CRANE: CT Robotic Arm and Needle Emplacer, a CT-compatible robot with a design focused on system dexterity that enables physicians to manipulate and insert needles within the scanner bore as naturally as they would be able to by hand. We define abstract and measurable clinically motivated metrics for in-bore dexterity applicable to general-purpose intra-bore image-guided needle placement robots, develop an automatic robot planning and control method for intra-bore needle manipulation and device setup, and demonstrate the redundant linkage design provides dexterity across various human morphology and meets the clinical requirements for target accuracy during an in-situ evaluation.

Figures (13)

• Figure 1: Needle insertion within imaging bores provides direct volumetric visualization of the anatomy and tool, improving the accuracy of needle insertion procedures such as retroperitoneal biopsy and lumbosacral spine nerve block. However, this enclosed environment limits the space for manipulation and line-of-site visibility for devices. CRANE overcomes these challenges with its cable-driven serial link design and integrated planning-control method to enable fully in-bore dexterous needle manipulation without requiring manual setup.
• Figure 2: Experimental setup for bench-top system evaluation, highlighting the robot platform: the gross positioning stage enables the platform's large workspace and houses the actuators for the in-bore joints, and the redundant cable-driven in-bore joints enable orientation control and reaching around obstacles. The clutching needle insertion axis allows deep needle insertion with a short robot stroke. Together, this provides CRANE with a large workspace and the capability to perform dynamic motions while remaining backdriveable and having a minimal in-bore cross-section.
• Figure 3: The robot end-effector is cable-driven. While cable drives provide low hysteresis and friction, they have limited stiffness, resulting in tracking errors. Joint mounted encoders enable direct sensing of the joints' position allowing controller compensation for cable stretch. The SMA actuated clutches temperature is sensed via thermistor, enabling closed-loop temperature control. The two moving and station clutches enable long travel active insertion or passive needle insertion with a simple and fail-passive mechanism which can be easily replaced for sterility and different size tools.
• Figure 4: The long cantilevered tube for in-bore joints causes deflection illustrated by FEA modeling. This error, not observed by the joint encoders, is tracked and compensated for using a 6-DoF magnetic tracker and end-effector feedback control.
• Figure 5: Kinematics diagram for the in-bore joints of CRANE. The base joints (outside of the image) are modeled as virtual-joints coinciding at the first in-bore joint and provide gross positioning providing cartesian linear motion. The idler pulleys enable cable pass-throughs and are located on all intermediate joints and links. The pulleys labeled on link 5 provide support for the drive cables for joints 6, 7, and 8.