Triple diffusion encoding MRI predicts intra-axonal and extra-axonal diffusion tensors in white matter

Area of Science:

• Neuroimaging
• Biophysics
• Diffusion MRI

Background:

• White matter (WM) integrity is crucial for neurological function.
• Conventional diffusion MRI struggles to differentiate intra-axonal and extra-axonal water diffusion.
• Advanced diffusion encoding techniques are needed to resolve diffusion compartments.

Purpose of the Study:

• To demonstrate the application of triple diffusion encoding (TDE) MRI.
• To separately estimate intra-axonal and extra-axonal diffusion tensors in white matter.
• To determine compartment-specific diffusion properties.

Main Methods:

• Acquired diffusion MRI data using a TDE pulse sequence with an axially symmetric b-matrix at 3T.
• Utilized specific axial and radial b-values and diffusion encoding directions.
• Applied a theoretical framework to estimate intra-axonal diffusivity and axonal water fraction.
• Acquired conventional single diffusion encoding data for tensor determination.

Main Results:

• Average intra-axonal diffusivity in WM was 2.24 ± 0.18 µm²/ms.
• Average axonal water fraction was 0.60 ± 0.11.
• Estimated compartment-specific diffusion parameters, including extra-axonal mean diffusivity (1.09 ± 0.19 µm²/ms) and fractional anisotropies.

Conclusions:

• Triple diffusion encoding (TDE) MRI enables separate estimation of diffusion tensors in intra-axonal and extra-axonal spaces of adult white matter.
• This technique allows for the determination of compartment-specific diffusion properties.
• TDE MRI offers a valuable tool for investigating white matter microstructure.