Diffusion MRI in Peripheral Nerves: Optimized b Values and the Role of Non-Gaussian Diffusion

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Diffusion-Weighted Imaging

Background:

• Diffusion-weighted imaging (DWI) offers insights into tissue microstructure beyond the central nervous system.
• Standard DWI parameters, often adapted from central nervous system protocols, may not be optimal for peripheral nerves.
• Peripheral nerve imaging requires tailored diffusion weighting schemes for accurate microstructural assessment.

Purpose of the Study:

• To determine the optimal diffusion imaging weighting scheme (b-domain) for peripheral nerves.
• To characterize tissue-specific diffusion behavior in peripheral nerves under healthy and diabetic conditions.
• To identify optimal b-values for diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) in peripheral nerves.

Main Methods:

• Prospective cross-sectional study involving 3-Tesla MR neurography of the sciatic nerve.
• Acquisition of DWI data with 16 b-values (0-1500 sec/mm²) in axial and radial directions.
• Analysis using monoexponential, biexponential, and kurtosis fitting models to assess diffusion behavior and goodness of fit.

Main Results:

• Non-Gaussian diffusion behavior was observed early, beyond 600 sec/mm² (axial) and 800 sec/mm² (radial).
• Biexponential and kurtosis models provided superior curve fits compared to the monoexponential model.
• Kurtosis-derived parameters (D and K) revealed significant differences between healthy volunteers and diabetic participants.

Conclusions:

• An optimal standard DWI/DTI protocol for peripheral nerve MR neurography is suggested with b = 700 sec/mm².
• This optimal b-value is substantially lower than typically used for the central nervous system.
• Tissue-specific optimization is crucial, and kurtosis parameters show promise as novel biomarkers for peripheral nerve disease.