Quantifying brain microstructure with diffusion MRI: Theory and parameter estimation.

Area of Science:

• Neuroscience
• Biophysics
• Medical Physics

Background:

• Diffusion Magnetic Resonance Imaging (dMRI) is crucial for understanding brain microstructure.
• Existing models often lack a unified physical framework, hindering comprehensive analysis.
• Neuronal tissue complexity requires advanced modeling approaches to capture microstructural details.

Purpose of the Study:

• To review, systematize, and discuss diffusion models within a coarse-graining physical context.
• To explore three major avenues of research in quantifying brain microstructure using diffusion.
• To highlight transient diffusion effects, long-time limit approximations, and multiple diffusion encoding techniques.

Main Methods:

• Systematic review and physical contextualization of diffusion models.
• Analysis of transient diffusion effects for microstructural length scale determination.
• Examination of long-time limit approximations and multiple diffusion encoding strategies.

Main Results:

• Transient diffusion effects reveal neuronal tissue length scales and structural disorder.
• Long-time diffusion signals can be modeled as nonexchanging anisotropic Gaussian components, though parameter estimation is challenging.
• Multiple diffusion encoding techniques access information beyond conventional diffusion propagators.

Conclusions:

• Diffusion models, viewed through coarse-graining, provide a framework for understanding brain microstructure.
• Transient effects and advanced encoding offer rich information about tissue physiology and pathology.
• Future research directions focus on mesoscopic transport in disordered systems for novel quantitative markers.