Fast and simplified mapping of mean axon diameter using temporal diffusion spectroscopy.

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Mapping axon diameter is crucial for diagnosing and monitoring neuronal pathologies.
• Current diffusion-weighted MRI methods for axon diameter measurement have limitations, including long scan times and complex data analysis, hindering clinical application.

Purpose of the Study:

• To introduce and validate a novel, fast, and model-free MRI metric, DDR⊥, for measuring mean axon diameters in the central nervous system.
• To assess the feasibility of using DDR⊥ for clinical applications in assessing white matter axon diameter.

Main Methods:

• Utilized temporal diffusion spectroscopy with oscillating diffusion gradients to measure mean axon diameters.
• Introduced DDR⊥ (the rate of dispersion of the perpendicular diffusion coefficient with gradient frequency) as a novel metric.
• Validated the method using computer simulations, ex vivo animal experiments, and in vivo human studies.

Main Results:

• DDR⊥ showed high sensitivity to small axons and correlated well with histological data in simulations and animal models.
• In vivo human studies demonstrated a strong correlation between DDR⊥ and reported mean axon diameters in the corpus callosum.
• The total scan time for DDR⊥ measurement was approximately 8 minutes.

Conclusions:

• DDR⊥ is a fast, simple, and model-free metric for mapping mean axon diameter in white matter.
• This method shows significant potential for clinical use in assessing axon diameter changes related to neuronal pathologies.
• DDR⊥ offers a promising advancement for non-invasive diagnosis and monitoring in neurology.