Functional tractography of white matter by high angular resolution functional-correlation imaging (HARFI)

Area of Science:

• Neuroimaging
• White Matter (WM) Neuroscience
• Functional MRI (fMRI)

Background:

• Resting-state BOLD signal correlations in white matter (WM) exhibit anisotropy, previously modeled using functional-correlation tensors.
• Functional-correlation tensors have limitations including noise sensitivity, orientation biases, and inability to detect complex functional orientation distributions (FODs).

Purpose of the Study:

• To introduce High-Angular-Resolution Functional-Correlation Imaging (HARFI) as a novel method to address limitations of existing tensor-based models for WM functional correlations.
• To characterize complex functional orientation distributions (FODs) in WM using HARFI.

Main Methods:

• Development and application of the HARFI model, analogous to High-Angular-Resolution Diffusion Imaging (HARDI).
• Utilizing a unique radial and angular sampling strategy within the HARFI framework.

Main Results:

• HARFI effectively eliminates orientation biases inherent in traditional tensor models.
• HARFI's FODs successfully reconstruct known WM pathways.
• HARFI detects asymmetric distributions like "bending" and "fanning," enabling new functional indices.

Conclusions:

• HARFI provides a robust and novel approach for assessing anisotropic BOLD signal changes in WM.
• The proposed asymmetric and functional indices may enhance fiber tracking specificity and delineate functional region boundaries.