Diffusion MRI with double diffusion encoding and variable mixing times disentangles water exchange from transient...

Area of Science:

• Diffusion MRI
• Quantitative MRI
• Biophysical modeling

Background:

• Double diffusion encoding (DDE) enhances diffusion MRI sensitivity to microstructural features.
• Correlation tensor imaging (CTI) and multi-Gaussian exchange (MGE) are DDE-based methods analyzing different microstructural properties.
• Both CTI and MGE utilize signal contrast between single and double diffusion encoding at the same b-value.

Purpose of the Study:

• To investigate the interplay between microscopic kurtosis (CTI) and exchange (MGE).
• To determine if microscopic kurtosis is sensitive to the exchange rate.
• To propose a novel method for disentangling exchange and transient kurtosis.

Main Methods:

• Monte Carlo simulations in various geometries with controlled exchange levels.
• Analysis of CTI and MGE parameter behavior under different exchange conditions.
• Development and testing of a new method, transient MGE (tMGE), incorporating transient kurtosis.

Main Results:

• Microscopic kurtosis derived from CTI is significantly affected by the exchange rate.
• Intercompartmental exchange and transient kurtosis are distinct contributors to microscopic kurtosis.
• tMGE demonstrates potential to differentiate between exchange and transient kurtosis based on mixing time dependence.

Conclusions:

• Microscopic kurtosis in CTI is not solely a measure of tissue complexity but is influenced by water exchange.
• The proposed tMGE method, using multiple mixing times and DDE, can potentially resolve exchange rates and kurtosis components.
• This advancement may lead to more accurate characterization of biological tissues using diffusion MRI.