Varying the Gradient Pulse Length Gives Valuable Information in NMR Diffusometry

1. Introduction NMR diffusometry has evolved to become one of the most important methods in the study of diffusion and flow of liquids in complex material. Material that may be investigated spans a broad range: From rocks to soft biological material. In the latter case, one is often faced with a problem of trying to separate effects from inhomogeneities and restrictions. In the former case, we mean a situation where the liquid has a diffusion coefficient that depends on position in the sample, due for instance, to differences in concentrations/densities across the sample. Moreover, the length over which these inhomogeneities persist must be longer than the Mean Square Displacement of the liquid during the diffusion time (i.e. the distance between the gradient pulses). In the latter case, we assume barriers, reflective or semipermeable, such that the diffusion is no longer Gaussian. Both of these effects give rise to curvature in Stejskal-Tanner plots. We present here an approach that allows one to separate these effects by making use of information conveyed from the variation of the gradient pulse length.