Dynamic NMR microscopy of gas phase Poiseuille flow

Dynamic NMR microscopy has been used to study xenon gas undergoing Poiseuil le flow in the regime where deterministic and stochastic motions are the sa me order of magnitude. For short observation time, the flow profile images are largely influenced by the longitudinal diffusion, manifested by large d isplacements in both positive and negative directions. For longer observati on time, the effect of the mixing between the fast and slow flow components due to transverse diffusion becomes apparent. A spin-echo version of the d ynamic NMR experiment yields images exhibiting strong distortions for longe r observation time due to fast diffusion under the "natural" gradient from magnetic field inhomogeneity (compared to results obtained with a stimulate d echo version). This effect is used as an edge-enhancement filter by emplo ying a longer time duration of the imaging gradient in a stimulated echo ex periment. (C) 2001 Academic Press.