Nuclear magnetic resonance microscopy in liquids using the dipolar field

We demonstrate theoretically and experimentally how the dipolar field can be used in nuclear magnetic resonance (NMR) to investigate the structure of heterogeneous liquid systems. Using the Fourier transformed dipolar field and magnetization distribution, a simple relation between the NMR signal generated by the dipolar field and the sample structure can be established. On the basis of this relation, theoretical models for periodic structures have been derived and used to analyze the variation of the NMR signal as a function of the spatial modulation imposed on the magnetization. If the spatial modulations imposed on the transverse and longitudinal magnetizations have the same wavelength, the signal generated by the dipolar field is a continuous function of the modulation wavelength and is sensitive to the structure of the sample. When this condition is not met, diffraction phenomena may be possible in periodic structures. To test the theoretical work, experimental data have been obtained from water surrounding randomly packed microspheres. These data are in agreement with the theoretical predictions and show that a resolution of the order of 10 mu m can be achieved fdr highly mobile systems. For spin bearing molecules, whose self-diffusion coefficient is two orders of magnitude less than that of free water, submicrometer resolution is expected. (C) 1997 American Institute of Physics.