Myelin water and tensor-valued diffusion imaging: (How) are they related?

Area of Science:

• Neuroimaging
• Quantitative MRI
• White Matter Microstructure

Background:

• Conventional MRI has limitations in characterizing central nervous system tissue microstructure.
• Quantitative MRI (qMRI) provides detailed microstructural information.
• Multi-metric qMRI approaches can improve understanding of healthy and diseased tissues.

Purpose of the Study:

• To investigate the relationship between myelin water fraction (MWF) and tensor-valued diffusion imaging metrics (microscopic FA - μFA, and C_MD).
• To characterize white matter microstructure in healthy individuals using these combined metrics.
• To evaluate the utility of these multi-metric approaches in assessing pathological changes, specifically in multiple sclerosis (MS).

Main Methods:

• Assessed relationships between MWF, FA, μFA, and C_MD in 25 healthy individuals using atlas comparison, correlation, and tract profiling.
• Applied z-score analysis and tract profiling in five individuals with MS to evaluate multi-metric utility in pathology.

Main Results:

• Tract profiling revealed consistent, tract-specific patterns for MWF, μFA, and C_MD in healthy white matter, resolving confounding factors seen in simple correlation.
• In MS, MWF, μFA, and C_MD demonstrated high sensitivity to pathology, identifying abnormalities in normal-appearing white matter and lesional areas.
• These metrics highlighted distinct types of tissue damage in MS.

Conclusions:

• Combining MWF, μFA, and C_MD provides a powerful multi-metric approach for assessing central nervous system microstructure.
• This approach enhances the investigation of development, aging, disease, and injury processes.
• The study demonstrates improved characterization of both healthy and pathological white matter.