Spatial coherence phenomena arising from translational spin motion in gradient spin echo experiments

The use of pulsed magnetic field gradients to encode spin magnetization for position or positional displacement leads to a variety of spatial coherenc es in the spin phases, each coherence being manifest in a characteristic di ffraction pattern, whether in k-space or q-space. These phenomena, which ar e sensitive to different temporal moments of the gradient waveform, range f rom the original Mansfield - Grannell position diffraction, through diffusi ve and flow diffraction, to diffraction patterns which arise owing to Taylo r dispersion in a heterogeneous velocity field. We describe each of these a nd suggest an appropriate terminology. Of particular recent interest is the double pulsed gradient spin echo nuclear magnetic resonance experiment, wh ich may be used to study stochastic processes in dispersive flow. We give a detailed analysis of this type of experiment, illustrated with the example of Poiseuille flow in a pipe. (C) 1999 John Wiley & Sons, Inc.