Sen, P. N., Schwartz, L. M., Mitra, P. P. (1994) Probing the structure of porous media using NMR spin echoes. Magnetic Resonance Imaging, 12 (2). pp. 227-230. ISSN 0730-725X
Abstract
The NMR pulsed field gradient spin-echo (PFGSE) amplitude M(k,t) is a direct measure of the diffusion propagator of the molecules of a fluid diffusing in the pores of a porous medium. For small values of k = γgδ, where g is the gradient strength, δ is the duration of the gradient pulse, and γ the gyromagnetic ratio, the PFGSE amplitude gives the diffusion coefficient D(t). The exact short-time diffusion coefficient, D(t)Do=1−(4DotS/(9Vpπ)−DotHS/(12Vp)+ptS/6Vp, provides an important method for determining the surface to pore-volume ratio SVp. Here the mean surface curvature H = 〈1R1 + 1R2〉. Combining early D(t) with the magnetization decay one obtains the surface relaxivity ϱ. The long-time effective diffusion constant derived from PFGSE gives information on the tortuosity of the connected space. The diffusion coefficient measured by PFGSE equals that derived from electrical conductivity only when ϱ = 0. Exact solutions with partially absorbing boundary conditions for a periodic structure are used to illustrate the influence of ϱ on the diffusion coefficient. M(k,t) can be well represented by a convolution of the structure factor of the connected pore space with an appropriate Gaussian propagator. This ansatz provides a model-independent way of obtaining the structure factor.
| Item Type: | Paper |
|---|---|
| Uncontrolled Keywords: | Restricted diffusion Porous medium NMR surface relaxation NMR pulsed field gradient Surfaceto-volume ratio Formation factor |
| Subjects: | physics > biophysics physics > fluid dynamics Investigative techniques and equipment > magnetic resonance imaging physics |
| CSHL Authors: | |
| Communities: | CSHL labs > Mitra lab |
| Depositing User: | CSHL Librarian |
| Date: | 1994 |
| Date Deposited: | 02 Apr 2012 20:31 |
| Last Modified: | 10 Feb 2017 20:36 |
| Related URLs: | |
| URI: | https://repository.cshl.edu/id/eprint/25878 |
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