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Self-diffusion measurements by a constant-relaxation method in strongly inhomogeneous magnetic fields
M Klein1, R Fechete, D E Demco
1Institut für Technische Chemie und Makromolekulare Chemie, Rheinisch-Westfälische Technische Hochschule, Worringerweg 1, Aachen D-52056, Germany.
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|September 27, 2003
Summary
This study validates a novel NMR method for measuring self-diffusion coefficients (D) in challenging conditions. The technique accurately quantifies diffusion in inhomogeneous fields, proving useful for materials like elastomers and biological tissues.
Area of Science:
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Materials Science
- Biophysics
Background:
- Standard NMR diffusion measurements often require homogeneous magnetic fields.
- Inhomogeneous fields, common in specialized NMR setups, pose challenges for accurate diffusion coefficient (D) determination.
- Existing methods may necessitate complex relaxation rate measurements.
Purpose of the Study:
- To investigate and validate a simple Hahn echo pulse sequence for measuring the self-diffusion coefficient (D) under constant-relaxation conditions.
- To evaluate the encoding of Hahn echo amplitude considering pulse flip angles and diffusion in the presence of inhomogeneous static and radiofrequency magnetic fields.
- To demonstrate the applicability of this method using a mobile one-sided NMR sensor (NMR-MOUSE).
Main Methods:
- Utilized a specific pulse sequence (thetax-tau1-2thetay-tau1+tau2-2thetay-tau2-Hahn echo) for diffusion measurements.
- Employed computer simulations incorporating spatial distribution of off-resonance fields, local field gradients, and pulse flip angles.
- Applied the method to a mobile NMR-MOUSE sensor with a bar magnet for liquid diffusion measurements.
- Investigated diffusion in elastomers and biological tissues.
Main Results:
- The NMR method accurately determined the self-diffusion coefficient (D) in the presence of strong magnetic field inhomogeneities.
- The technique proved effective for measuring solvent diffusion in elastomers without needing transverse relaxation rates.
- A correlation was found between the self-diffusion coefficient of toluene in natural rubber and its crosslink density.
- Diffusion anisotropy of water in bovine Achilles tendon was successfully measured.
Conclusions:
- The investigated Hahn echo pulse sequence is a robust method for measuring self-diffusion coefficients (D) even in strongly inhomogeneous magnetic fields.
- This NMR approach offers a simplified and effective way to study diffusion in complex materials like elastomers and biological tissues.
- The method's utility is highlighted by its application in correlating polymer crosslink density with solvent diffusion and measuring diffusion anisotropy in tendons.