Characterizing intra-axonal water diffusion with direction-averaged triple diffusion encoding MRI.

Area of Science:

• Neuroimaging
• Biophysics
• Diffusion MRI

Background:

• Diffusion MRI (dMRI) signal in white matter is dominated by intra-axonal water at high diffusion weightings.
• Characterizing intra-axonal diffusion properties offers insights into pathology.
• Traditional Stejskal-Tanner sequences struggle to reliably estimate intra-axonal diffusivity and water fraction.

Purpose of the Study:

• To develop and validate a modified diffusion MRI sequence for accurate estimation of intra-axonal diffusion properties.
• To enable reliable quantification of intra-axonal diffusivity and water fraction.

Main Methods:

• Implementation of a triple diffusion encoding (TDE) MRI sequence, a modification of the Stejskal-Tanner sequence.
• Addition of orthogonal diffusion encoding gradients to the primary gradients.
• Application of analytic formulae to direction-averaged dMRI data from the TDE sequence.

Main Results:

• The proposed TDE sequence allows for the determination of intra-axonal diffusivity and water fraction.
• Numerical simulations indicate accuracy for b-values of 4000 s/mm² and higher.
• The method provides reliable estimates for key intra-axonal diffusion parameters.

Conclusions:

• The TDE MRI sequence is a promising tool for characterizing intra-axonal diffusion in white matter.
• This technique can enhance the biophysical interpretation of diffusion changes in neurological diseases.
• Accurate quantification of intra-axonal properties is achievable with the proposed method.