Peripheral Nerve Focused Ultrasound Lesioning-Visualization and Assessment Using Diffusion Weighted Imaging

Matthew R Walker; Jidan Zhong; Adam C Waspe; Karolina Piorkowska; Lananh N Nguyen; Dimitri J Anastakis; James M Drake; Mojgan Hodaie

doi:10.3389/fneur.2021.673060

Peripheral Nerve Focused Ultrasound Lesioning-Visualization and Assessment Using Diffusion Weighted Imaging

Front Neurol. 2021 Jul 9:12:673060. doi: 10.3389/fneur.2021.673060. eCollection 2021.

Authors

Matthew R Walker^{1

2}, Jidan Zhong², Adam C Waspe^{3

4}, Karolina Piorkowska³, Lananh N Nguyen⁵, Dimitri J Anastakis^{1

2

6}, James M Drake^{1

3

7}, Mojgan Hodaie^{1

2

8}

Affiliations

¹ Institute of Medical Science, University of Toronto, Toronto, ON, Canada.
² Division of Brain, Imaging & Behaviour, Krembil Research Institute, University Health Network, Toronto, ON, Canada.
³ Centre for Image Guided Innovation and Therapeutic Intervention, Hospital for Sick Children, Toronto, ON, Canada.
⁴ Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.
⁵ Laboratory Medicine Program, University Health Network and University of Toronto, Toronto, ON, Canada.
⁶ Department of Surgery, Toronto Western Hospital, University Health Network and University of Toronto, Toronto, ON, Canada.
⁷ Department of Neurosurgery, Hospital for Sick Children, Toronto, ON, Canada.
⁸ Department of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, ON, Canada.

Abstract

Objectives: Magnetic resonance-guided focused ultrasound (MRgFUS) is a non-invasive targeted tissue ablation technique that can be applied to the nervous system. Diffusion weighted imaging (DWI) can visualize and evaluate nervous system microstructure. Tractography algorithms can reconstruct fiber bundles which can be used for treatment navigation and diffusion tensor imaging (DTI) metrics permit the quantitative assessment of nerve microstructure in vivo. There is a need for imaging tools to aid in the visualization and quantitative assessment of treatment-related nerve changes in MRgFUS. We present a method of peripheral nerve tract reconstruction and use DTI metrics to evaluate the MRgFUS treatment effect. Materials and Methods: MRgFUS was applied bilaterally to the sciatic nerves in 6 piglets (12 nerves total). T1-weighted and diffusion images were acquired before and after treatment. Tensor-based and constrained spherical deconvolution (CSD) tractography algorithms were used to reconstruct the nerves. DTI metrics of fractional anisotropy (FA), and mean (MD), axial (AD), and radial diffusivities (RD) were measured to assess acute (<1-2 h) treatment effects. Temperature was measured in vivo via MR thermometry. Histological data was collected for lesion assessment. Results: The sciatic nerves were successfully reconstructed in all subjects. Tract disruption was observed after treatment using both CSD and tensor models. DTI metrics in the targeted nerve segments showed significantly decreased FA and increased MD, AD, and RD. Transducer output power was positively correlated with lesion volume and temperature and negatively correlated with MD, AD, and RD. No correlations were observed between FA and other measured parameters. Conclusions: DWI and tractography are effective tools for visualizing peripheral nerve segments for targeting in non-invasive surgical methods and for assessing the microstructural changes that occur following MRgFUS treatment.

Keywords: diffusion tensor imaging; diffusion weighted imaging; high intensity focused ultrasound; magnetic resonance-guided focused ultrasound; neuromodulation; peripheral nerves; tractography.