Using light and X-ray scattering to untangle complex neuronal orientations and validate diffusion MRI

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Mapping human brain connectivity relies on understanding nerve fiber trajectories and axonal orientations.
• Axonal crossings at the micrometer scale present challenges for traditional imaging methods.
• Diffusion magnetic resonance imaging (dMRI) offers insights into axonal alignment but lacks spatial resolution and specificity.

Purpose of the Study:

• To apply and cross-validate scattered light imaging (SLI) and small-angle X-ray scattering (SAXS) for mapping axonal orientations.
• To establish ground-truth data for validating dMRI in brain connectivity research.
• To investigate complex fiber architecture in human and animal brain sections.

Main Methods:

• Simultaneous application of SLI and SAXS on identical human and vervet monkey brain sections.
• Quantitative comparison of in-plane and through-plane fiber orientation data from SLI, SAXS, and dMRI.
• Validation of theoretical predictions using SAXS and dMRI data.

Main Results:

• SLI and SAXS demonstrated quantitative agreement in determining in-plane fiber orientations, including areas with crossing fibers.
• dMRI results showed good agreement with scattering techniques in most voxels, with minor discrepancies.
• SAXS and dMRI confirmed theoretical models for SLI's through-plane orientation measurements.

Conclusions:

• SLI and SAXS provide high-resolution, specific, and quantitative 3D axonal orientation mapping at the micrometer scale.
• These scattering techniques serve as a crucial tool for validating and improving dMRI-based brain connectivity analysis.
• The findings facilitate advanced investigations into the intricate fiber architecture of the brain.