Free water elimination tractometry for aging brains.

Area of Science:

• Neuroimaging
• Biomedical Engineering
• Gerontology

Background:

• Diffusion MRI tractometry is crucial for studying brain connections in aging.
• Increased white matter free water in aging brains can reduce tractometry reliability.
• Existing methods may not fully account for age-related changes in white matter microstructure.

Purpose of the Study:

• To evaluate the impact of free water elimination (FWE) and multi-shell multi-tissue (MSMT) modeling on tractometry reliability and accuracy in older adults.
• To assess the generalizability of findings to single-shell diffusion MRI datasets.
• To investigate the relationship between tractometry metrics and white matter hyperintensity burden.

Main Methods:

• Applied FWE and MSMT modeling to diffusion MRI data from 396 older adults (65-103 years).
• Assessed tractometry reliability using split-half comparisons across the analysis pipeline.
• Correlated tractometry outcomes with Fazekas scores for white matter hyperintensity burden.
• Simulated single-shell data from multi-shell datasets to test generalizability.

Main Results:

• Both FWE and MSMT modeling significantly improved tractometry reliability and accuracy.
• FWE enhanced tractography yield and coverage in areas with leukoaraiosis.
• Tractometry findings were strongly predictive of Fazekas scores, indicating global white matter changes.
• Results generalized to single-shell data, suggesting applicability to diverse datasets.

Conclusions:

• Accounting for free water is essential for reliable and accurate tractometry in aging brains.
• FWE and MSMT modeling offer robust solutions for analyzing white matter integrity in older populations.
• The findings underscore the impact of white matter hyperintensities on overall brain connectivity.