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Microscopic anisotropy revealed by NMR double pulsed field gradient experiments with arbitrary timing parameters
Evren Ozarslan1, Peter J Basser
1Section on Tissue Biophysics and Biomimetics, NICHD, NIH, Bethesda, MD 20892, USA. evren@helix.nih.gov
The Journal of Chemical Physics
|April 25, 2008
Summary
This study provides an exact NMR signal attenuation formula for restricted geometries, enabling pore size estimation and anisotropy measurement in diffusion MRI. It differentiates restricted from free diffusion and characterizes pore dimensions.
Area of Science:
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Diffusion Magnetic Resonance Imaging (dMRI)
- Physical Chemistry
Background:
- Pulsed field gradient (PFG) NMR is crucial for studying molecular diffusion.
- Analyzing diffusion in restricted geometries (e.g., pores) is challenging.
- Understanding microscopic anisotropy is key to interpreting dMRI data.
Purpose of the Study:
- To derive an exact expression for NMR signal attenuation in restricted geometries.
- To develop methods for differentiating diffusion types and estimating pore dimensions.
- To explore the measurement of microscopic anisotropy and pore structure.
Main Methods:
- General double pulsed field gradient (PFG) experiment formulation.
- Calculation of NMR signal attenuation for arbitrary parameters.
- Application to parallel plates, cylinders, and spheres.
Main Results:
- An exact expression for NMR signal attenuation in restricted geometries at long wavelengths.
- Demonstration of observing microscopic anisotropy induced by pore boundaries.
- Explicit solutions for diffusion in various pore shapes, including cylinders and spheres.
- Simultaneous measurement of cylinder orientation and diameter in packed structures.
Conclusions:
- The developed method allows differentiation of restricted diffusion from free or multicompartmental diffusion.
- It enables estimation of characteristic pore dimensions and microscopic anisotropy.
- The approach is applicable to various pore geometries and can characterize complex structures like coherently packed cylinders.
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