Background and aims

Diffusion-weighted imaging has been used to quantify peripheral nerve properties; however, traditional post-processing techniques have several limitations. Advanced neuroimaging techniques, which overcome many of these limitations, have not been applied to peripheral nerves. Here, we use state-of-the-art diffusion analysis tools to reconstruct the median and ulnar nerves and quantify their diffusion properties.

Methods

Diffusion-weighted MRI scans were obtained from eight healthy adult subjects. Constrained spherical deconvolution was combined with probabilistic fibre-tracking to compute track-weighted fibre orientation distribution (TW-FOD). The tensor was computed and used along with the tracks to estimate track-weighted apparent diffusion coefficient (TW-ADC), track-weighted fractional anisotropy (TW-FA), track-weighted axial diffusivity (TW-AD) and track-weighted radial diffusivity (TW-RD). Variability of track-weighted measurements was used to estimate power size information.

Results

The population inter-session mean (± standard deviation) measurements for the median nerve were: TW-FOD 1.30 (±0.17), TW-ADC 1.16 (±0.13) × 10-3 mm2/s, TW-FA 0.60 (±0.05), TW-AD 2.05 (±0.16) × 10-3 mm2/s, and TW-RD 0.72 (±0.12) × 10-3 mm2/s. The corresponding measurements for the ulnar nerve were: TW-FOD 1.30 (±0.17), TW-ADC 1.16 (±0.13) × 10-3 mm2/s, TW-FA 0.60 (±0.05), TW-AD 2.05 (±0.16) × 10-3 mm2/s, and TW-RD 0.72 (±0.12) × 10-3 mm2/s.

Interpretation

State-of-the-art neuroimaging techniques were used to quantify the median and ulnar nerve properties. A sample size of 37 would be sufficient to detect a 10% difference in any of the measured track-weighted metrics. A sample size of 20 would be large enough to detect within-subject differences as small as 2.9% (TW-AD, ulnar nerve) and between-subject differences as small as 3.8% (TW-AD, ulnar nerve).

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