Measurement of translational displacement probabilities by NMR: an indicator of compartmentation

We introduce and demonstrate an NMR pulsed gradient stimulated echo method of directly obtaining the molecular translational displacement probability (displacement profile) of a liquid. The temporal development of the displacement profile reflects the presence of diffusion, restrictions to diffusion (e.g., walls, membranes), flow, and spatially dependent relaxation sinks. This approach allows the study of compartments which are too small to be observed by conventional NMR imaging methods. The distribution of spatial properties of compartments can be characterized over a spatial field of about 0.1 to 25 microns, completely independent of the absolute spatial location of the individual compartments.