Body-mounted robotic assistant for MRI-guided low back pain injection

Abstract

Purpose-This paper presents the development of a body-mounted robotic assistant for magnetic resonance imaging (MRI)-guided low back pain injection. Our goal was to eliminate the radiation exposure of traditional X-ray guided procedures while enabling the exquisite image quality available under MRI. The robot is designed with a compact and lightweight profile that can be mounted directly on the patient's lower back via straps, thus minimizing the effect of patient motion by moving along with the patient. The robot was built with MR-Conditional materials and actuated with piezoelectric motors so it can operate inside the MRI scanner bore during imaging and therefore streamline the clinical workflow by utilizing intraoperative MR images. Methods-The robot is designed with a four degrees-of-freedom (DOF) parallel mechanism, stacking two identical Cartesian stages, to align the needle under intraoperative MRI-guidance. The system targeting accuracy was first evaluated in free space with an optical tracking system, and further assessed with a phantom study under live MRI-guidance. Qualitative imaging quality evaluation was performed on a human volunteer to assess the image quality degradation caused by the robotic assistant. Results-Free space positioning accuracy study demonstrated that the mean error of the tip position to be 0.51 ± 0.27mm and needle angle to be 0.70 ± 0.38°. MRI-guided phantom study indicated the mean errors of the target to be 1.70±0.21mm, entry point to be 1.53 ± 0.19mm, and needle angle to be 0.66 ±0.43°. Qualitative imaging quality evaluation validated that the image degradation caused by the robotic assistant in the lumbar spine anatomy is negligible. Conclusions-The study demonstrates that the proposed body-mounted robotic system is able to perform MRI-guided low back injection in a phantom study with sufficient accuracy and with minimal visible image degradation that should not affect the procedure.

MRI-guided lumbar spinal injections with body-mounted robotic system: cadaver studies

“…The experiment results indicate four main factors that lead to the cannula placement errors of the robot-assisted approach: (1) mechanism errors, including fabrication/assembly tolerance, backlash of timing belts, deformation of plastic materials, etc., (2) imaging errors, including image resolution, registration accuracy, cannula artifacts, etc., (3) skin elasticity variations at the entry point, and (4) cannula bending. The error sources of the mechanism and imaging factors were analyzed in our previous study on free space evaluation and MRI phantom study with a reported target position error of 1.70±0.21mm and insertion angle error of 0.66±0.43 • [23]. Significant skin deformation at the entry point was observed during the initial test insertions into the cadaver, especially as the tissue dried out over the time, which caused bending and deviation of the cannula trajectory and consequently failure of reaching targets.…”

“…Hence, this system is considered to be an MRI-Conditional system. A detailed description of the mechanical design is reported in [23].…”

“…The desired target and entry points are determined by the radiologist on the surgical planning workstation and transmitted to the robot control software through the OpenIGTLink communication protocol [26]. Based on that, the robot control software solves the kinematics [23] and generates motion commands for each axis, which are transferred to the robot controller to move the robot and align the cannula to the planned pose. Once the cannula is aligned, the radiologist will insert the cannula manually.…”

“…In our previous study, we have developed a 4-DOF body-mounted robotic assistant for low back injections under intraoperative MRI guidance [23]. The mechanical design, robot kinematics and registration were reported, and the system positioning accuracy was assessed in free space and with an MRI-guided phantom study.…”

Anesthetic considerations in spine surgery: What orthopaedic surgeon should know!

“…7 Body-mounted robotic assistant for magnetic resonance imaging (MRI)-guided low back pain injections is another budding modality in the armamentarium for refractory low back pain without exposure to radiation. 8 General anesthesia is usually preferred for all kinds of surgical procedures involving the spine due to better patient tolerance, secure airway, better surgical exposure under muscle relaxants, early postoperative exam without the confounding results from conventional epidural anesthetic agents, and better control of intraoperative hemodynamic changes. However, it has its own risks, particularly in patients with increased age and cardiopulmonary disorders.…”