Sensitivity of quantitative diffusion MRI tractography and microstructure to anisotropic spatial sampling.

Area of Science:

• Neuroimaging
• Diffusion MRI
• White Matter Tractography

Background:

• Diffusion weighted MRI (dMRI) models neural structure and white matter variations.
• Anisotropic voxels in dMRI tractography introduce biases not fully characterized.
• Previous work showed connectome graph measures vary with spatial sampling.

Purpose of the Study:

• Characterize biases from anisotropic voxels in dMRI.
• Investigate effects on microstructural measures (fractional anisotropy, mean diffusivity) and white matter bundle properties (volume, length, surface area).
• Understand the impact of spatial resolution on dMRI data quality.

Main Methods:

• Assessed statistical significance of dMRI measures using Wilcoxon Signed-Rank test.
• Compared three white matter bundles across resolutions in 44 subjects (Human Connectome Project - Young Adult).
• Explored resolutions from 1.25 mm isotropic to 6 anisotropic resolutions, then upsampled to 1.25 mm and 1 mm isotropic.

Main Results:

• Statistically significant differences (p≤0.05) in microstructural and bundle measures were found at all resolutions.
• Cohen's d coefficient quantified the effect size of anisotropic voxels.
• Anisotropic voxels significantly impacted microstructure and tractography outcomes.

Conclusions:

• Basic up-sampling cannot fully recover fractional anisotropy and mean diffusivity from low-quality data.
• White matter bundle measures showed improved repeatability after resampling to 1 mm isotropic resolution.
• Spatial resolution critically influences dMRI-derived measures and their reliability.