Conventions and nomenclature for double diffusion encoding NMR and MRI.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Biophysics

Background:

• The Stejskal and Tanner pulsed field gradient design (1965) is foundational for diffusion NMR and MRI in microstructural analysis.
• Conventional diffusion MRI methods face limitations in resolving complex microstructural details.
• Novel techniques like double diffusion encoding (DDE) NMR and MRI show promise for advanced quantifiable metrics.

Purpose of the Study:

• To establish a consensus on terminology for double diffusion encoding (DDE) pulse sequences, parameters, and derived metrics.
• To elucidate the regimes where DDE provides unique microstructural information unobtainable by conventional methods.
• To highlight DDE's potential for determining microscopic diffusion anisotropy and microscopic fractional anisotropy.

Main Methods:

• Development and application of double diffusion encoding (DDE) NMR and MRI pulse sequences.
• Comparative analysis of DDE-derived metrics against conventional diffusion MRI acquisitions.
• Model-free elucidation of microstructural information obtainable through DDE.

Main Results:

• A consensus on DDE terminology and associated concepts has been established among active research groups.
• DDE metrics provide microstructural information not achievable with conventional diffusion MRI in a model-free manner.
• DDE enables determination of microscopic diffusion anisotropy and microscopic fractional anisotropy, complementary to macroscopic fractional anisotropy.

Conclusions:

• Standardized DDE terminology facilitates consistent research and application of this advanced diffusion MRI technique.
• DDE offers unique insights into microstructural features, independent of orientation dispersion.
• DDE holds significant future potential for detailed microstructural characterization in various scientific domains.