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

Area of Science:

• Neuroscience
• Medical Imaging
• Biomedical Engineering

Background:

• Magnetic resonance-guided focused ultrasound (MRgFUS) offers non-invasive tissue ablation for the nervous system.
• Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are crucial for assessing nerve microstructure.
• Advanced imaging tools are needed to evaluate MRgFUS-induced nerve changes.

Purpose of the Study:

• To develop and validate a method for peripheral nerve tract reconstruction using DWI and tractography.
• To quantitatively assess acute microstructural nerve changes following MRgFUS treatment using DTI metrics.
• To correlate MRgFUS parameters with observed treatment effects.

Main Methods:

• MRgFUS was applied to the sciatic nerves of 6 piglets.
• T1-weighted and diffusion images were acquired pre- and post-treatment.
• Tensor and constrained spherical deconvolution (CSD) tractography reconstructed nerve bundles.
• DTI metrics (FA, MD, AD, RD) and MR thermometry evaluated treatment effects.
• Histological analysis confirmed lesion formation.

Main Results:

• Successful reconstruction of sciatic nerves was achieved in all subjects.
• Tractography revealed disruption of nerve fiber bundles post-MRgFUS.
• Significant changes in DTI metrics (decreased FA, increased MD, AD, RD) indicated acute microstructural damage.
• Higher transducer output power correlated with larger lesion volumes, increased temperature, and more pronounced DTI metric changes.

Conclusions:

• DWI and tractography are effective for visualizing peripheral nerves during MRgFUS procedures.
• These imaging techniques accurately assess MRgFUS-induced microstructural nerve alterations.
• The findings support the use of DWI and tractography for guiding and evaluating non-invasive nerve treatments.