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Intra-axonal diffusivity in brain white matter.

Bibek Dhital¹, Marco Reisert¹, Elias Kellner¹

¹Department of Diagnostic Radiology, University Medical Center, University of Freiburg, Freiburg, 79106, Germany.

|January 20, 2019

Summary

This summary is machine-generated.

This study measures intra-axonal diffusivity in white matter using a novel diffusion-weighted MRI method. The findings provide crucial parameters for biophysical modeling, improving the understanding of tissue cellular structure.

Keywords:

Diffusion MRI Diffusion encoding Intra-axonal diffusivity Micro-structure imaging Orientation dispersion Planar encoding White matter

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Area of Science:

Neuroimaging
Biophysics
Diffusion MRI

Background:

Biophysical modeling of tissue cellular structure relies on diffusion-weighted MRI (DW-MRI).
Accurate estimation of diffusion parameters within specific cellular compartments, like intra-axonal water diffusivity, is challenging due to signal degeneracy and complex diffusion phenomena.
Existing DW-MRI methods struggle with unambiguous parameter estimation due to confounding signals from multiple tissue compartments and fiber orientation dispersion.

Purpose of the Study:

To accurately measure intra-axonal water diffusivity, a key parameter for white matter biophysical models.
To overcome limitations in current DW-MRI techniques that hinder precise estimation of intra-axonal diffusivity.
To provide reliable in vivo measurements of intra-axonal diffusivity for improved biophysical modeling.

Main Methods:

Development and application of a planar water mobility filter to suppress signals from extra-axonal water and off-axis oriented cellular processes.
Measurement of the remaining intra-axonal signal's diffusivity using linear and spherical diffusion encoding after signal suppression.
Utilized Stejskal-Tanner diffusion-weighted MRI data acquisition.

Main Results:

Successfully measured the average intra-axonal diffusivity (D0) as 2.25±0.03 μm²/ms for the applied gradient timing.
Extrapolated the intra-axonal diffusivity to infinite diffusion time (D0(∞)) yielding approximately 2.0 μm²/ms.
Demonstrated that the measured intra-axonal diffusivity imposes significant constraints on parameter selection for DW-MRI biophysical models.

Conclusions:

The developed method enables precise measurement of intra-axonal diffusivity, a critical parameter in neuroimaging.
These findings significantly advance the accuracy and reliability of biophysical modeling for white matter.
The results highlight the importance of accounting for intra-axonal water diffusivity in DW-MRI analysis for a better understanding of tissue microstructure.