Investigating white matter fibre density and morphology using fixel-based analysis

Area of Science:

• Neuroimaging
• Diffusion MRI
• White Matter Analysis

Background:

• Voxel-based diffusion MRI analysis faces limitations due to crossing fibres, leading to non-specific measures.
• Higher-order diffusion models allow extraction of fibre-specific parameters (fixels) but lack macroscopic morphological information.

Purpose of the Study:

• Introduce Fixel-Based Morphometry (FBM) to quantify white matter bundle morphology (cross-section).
• Integrate FBM with fibre density measures within a comprehensive fixel-based analysis framework.
• Develop combined measures of fibre density and cross-section for a more complete axonal count estimation.

Main Methods:

• Developed Fixel-Based Morphometry (FBM) to assess white matter bundle morphology.
• Utilized higher-order diffusion models to extract microscopic fibre density (fixels).
• Performed simulations with a fibre bundle phantom and compared clinical vs. control groups.

Main Results:

• FBM quantifies macroscopic white matter morphology (cross-section).
• Simulations demonstrated the utility of fibre density, cross-section, and combined measures.
• Clinical group comparison showed distinct and complementary information from all three measures.

Conclusions:

• FBM provides crucial macroscopic information complementary to microscopic fibre density.
• Combined fibre density and cross-section measures offer enhanced sensitivity and interpretability for detecting pathologies.
• The comprehensive fixel-based analysis framework advances white matter investigation in neuroimaging.