Quantifying myelin in crossing fibers using diffusion-prepared phase imaging: Theory and simulations

Area of Science:

• Neuroimaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Current MRI techniques offer averaged myelin estimates, insufficient for complex white matter.
• Differentiating myelination in crossing fibers is crucial for precise neuroimaging.

Purpose of the Study:

• To develop and validate a novel MRI technique for estimating myelin content in individual fiber populations.
• To overcome limitations of voxel-averaged myelin measurements in the human brain.

Main Methods:

• Diffusion-prepared phase imaging (DIPPI) sequence was developed.
• Phase accumulation of diffusion-weighted MRI signal was measured.
• Simulations and phantom data were used to quantify phase sources and estimate log g-ratio.

Main Results:

• DIPPI leverages phase accumulation sensitive to myelin.
• Diffusion-weighting enhances intra-axonal water signal and provides directional information.
• Estimated biases for in vivo parameters were quantified for eddy currents, extra-axonal signal, and off-resonance fields.

Conclusions:

• DIPPI enables distinguishing myelination in crossing fibers within a single voxel.
• This technique offers a more specific marker for myelination compared to existing methods.
• Potential for per-fiber population g-ratio estimation in vivo.