Rotating-frame-imaging technique for spatially resolved diffusion and flow studies in the fringe field of RF probe coils

A method for rotating-frame NMR diffusometry in the fringe-field B-1 gradients of solenoid RF coils in standard probeheads is described. A 5 mm RF solenoid coil, for instance, produces B-1 gradients of up to 3.3 T/m. The gradients can be enhanced by so-called flux concentrators so that values comparable to those common in laboratory-frame PGSE experiments should be feasible, The principle of the technique is to produce a z magnetization grid with the aid of a B-1 gradient pulse, The wavenumber of the grid is varied by the length of the preparation pulse. After a certain diffusion delay, the grid is rendered as an image using a rapid rotating-frame-imaging technique. The B-1 gradient need not be constant, Diffusion coefficients are rather evaluated locally based on the local B-1 gradients. Single-transient diffusion experiments in toroid resonators, and the employment of the B-1 gradients produced by the skin effect of conducting materials are suggested. (C) 1996 Academic Press, Inc.