DIFFUSIONAL EDGE ENHANCEMENT OBSERVED BY NMR IN THIN GLASS-CAPILLARIES

In NMR microscopy the effect of molecular diffusion is usually to degrade resolution and sensitivity due to destructive interference of signals from the moving spins. In samples there may exist regions that differ markedly in the translational diffusion coefficient of the molecules whose spatial distribution is being imaged, and in particular, samples may contain barriers impermeable to the translating spins. We present an experimental demonstration that, in the presence of a magnetic field gradient, a reduction in the translational mean free path of liquid molecules, due to barriers, results in the enhancement of magnetization near barriers. Monte Carlo simulations are compared with experiments. The observed effects are induced by barriers, not compartmentalization. This edge enhancement may provide a means through NMR microscopy of visualizing small impermeable structures that might otherwise be invisible.