Quantitative mapping of the per-axon diffusion coefficients in brain white matter

Area of Science:

• Neuroimaging
• Biophysics
• Diffusion MRI

Background:

• Diffusion MRI probes tissue microstructure.
• Intravoxel fiber orientation distribution complicates diffusion measurements.
• Accurate estimation of per-axon diffusion coefficients is crucial.

Purpose of the Study:

• To present a simple method for estimating diffusion coefficients parallel and perpendicular to axons.
• To obtain per-axon or microscopic diffusion coefficients.
• To achieve estimates unconfounded by intravoxel fiber orientation distribution.

Main Methods:

• Utilizing Diffusion MR imaging.
• Exploiting the invariance of the spherical mean of the diffusion signal over gradient directions.
• Proposing the spherical mean technique (SMT) for estimating per-axon diffusion coefficients.

Main Results:

• Demonstrated quantitative maps of axon-scale diffusion in human brain white matter.
• Successfully factored out effects of fiber dispersion and crossing.
• Estimated microscopic diffusion coefficients in vivo using standard MRI sequences.

Conclusions:

• Per-axon diffusion coefficient estimation is vital for accurate fiber orientation recovery.
• The spherical mean technique distinguishes microscopic tissue features from fiber dispersion.
• This method may improve sensitivity and specificity for neurological conditions.