The Pseudo-Fiber Effect: Fiber Density Impacts on Diffusion Metrics

Motivation: To understand how axon density affects degeneracy-related errors in diffusion metric estimation. Goal(s): Assuming ideal conditions (e.g., noise free and no inter-compartmental exchange), are there correlations between voxel contents and model degeneracies? Approach: A systematically-generated set of simulated voxels spanning a wide range of microstructural compositions, processed with various diffusion models, and analyzed both comparatively and component-wise. Results: Based on the individual signal component results, the extra-axonal water is the largest confounding factor. A model's depends largely on its ability to distinguish truly intra-axonal water from constrained extra-axonal water. Impact: It is important to consider degeneracies when interpreting the results of diffusion modeling lest the associated errors propagate downstream. Our results offer a more robust understanding of the conditions which give rise to these degeneracy-related errors.