Fiber-specific age-related differences in the white matter of healthy adults uncovered by fixel-based analysis

Area of Science:

• Neuroimaging
• Neuroscience
• Aging Research

Background:

• Diffusion MRI is commonly used to study white matter (WM) aging.
• Conventional voxel-based analysis using fractional anisotropy (FA) may miss age-related microstructural changes.
• FA conflates multiple fiber populations within a voxel, limiting detection of fiber-specific alterations.

Purpose of the Study:

• To investigate age associations within individual white matter fiber populations using fixel-based analysis (FBA).
• To determine if age-related degeneration affects specific fiber tracts independently of overall FA changes.

Main Methods:

• Utilized fixel-based analysis (FBA) on diffusion MRI data from 541 healthy adults (aged 36-100 years).
• Examined age associations for individual fiber populations (fixels) within complex white matter architectures.
• Compared findings with conventional voxel-based analysis relying on fractional anisotropy (FA).

Main Results:

• Identified significant age associations in fixel-based measures for individual fiber populations.
• Demonstrated that different crossing fiber populations exhibit distinct age-related changes.
• Observed selective degeneration in specific intravoxel white matter fibers that did not alter overall FA.

Conclusions:

• Fixel-based analysis provides a more sensitive approach to detecting age-related white matter degeneration than traditional methods.
• Selective degeneration of specific fiber populations occurs during aging, potentially independent of changes in overall FA.
• These findings highlight the importance of analyzing individual fiber tracts for a comprehensive understanding of brain aging.