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

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 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 <inline-formula id="IEq1"><alternatives><math><mrow><mn>0.51</mn><mo>±</mo><mn>0.27</mn></mrow></math><tex-math id="IEq1_TeX">\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.51\pm 0.27$$\end{document}</tex-math><inline-graphic href="11548_2019_2080_Article_IEq1.gif"></inline-graphic></alternatives></inline-formula>mm and needle angle to be <inline-formula id="IEq2"><alternatives><math><mrow><mn>0</mn><mo>.</mo><msup><mn>70</mn><mo>°</mo></msup><mo>±</mo><mn>0</mn><mo>.</mo><msup><mn>38</mn><mo>°</mo></msup></mrow></math><tex-math id="IEq2_TeX">\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.70^\circ \pm 0.38^\circ $$\end{document}</tex-math><inline-graphic href="11548_2019_2080_Article_IEq2.gif"></inline-graphic></alternatives></inline-formula>. MRI-guided phantom study indicated the mean errors of the target to be <inline-formula id="IEq3"><alternatives><math><mrow><mn>1.70</mn><mo>±</mo><mn>0.21</mn></mrow></math><tex-math id="IEq3_TeX">\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.70\pm 0.21$$\end{document}</tex-math><inline-graphic href="11548_2019_2080_Article_IEq3.gif"></inline-graphic></alternatives></inline-formula>mm, entry point to be <inline-formula id="IEq4"><alternatives><math><mrow><mn>1.53</mn><mo>±</mo><mn>0.19</mn></mrow></math><tex-math id="IEq4_TeX">\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.53\pm 0.19$$\end{document}</tex-math><inline-graphic href="11548_2019_2080_Article_IEq4.gif"></inline-graphic></alternatives></inline-formula>mm, and needle angle to be <inline-formula id="IEq5"><alternatives><math><mrow><mn>0</mn><mo>.</mo><msup><mn>66</mn><mo>°</mo></msup><mo>±</mo><mn>0</mn><mo>.</mo><msup><mn>43</mn><mo>°</mo></msup></mrow></math><tex-math id="IEq5_TeX">\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.66^\circ \pm 0.43^\circ $$\end{document}</tex-math><inline-graphic href="11548_2019_2080_Article_IEq5.gif"></inline-graphic></alternatives></inline-formula>. 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.