Effects of barrier‐induced nuclear spin magnetization inhomogeneities on diffusion‐attenuated MR signal

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Abstract
The spatial distribution of the transverse nuclear spin magnetization, appearing in a single compartment with impermeable boundaries in a Stejskal‐Tanner gradient pulse MR experiment, is analyzed in detail. At short diffusion times the presence of diffusion‐restrictive barriers (membranes) reduces effective diffusivity near the membranes and leads to an inhomogeneous spin magnetization distribution (the edge‐enhancement effect). In this case, the signal reveals a quasi‐two‐compartment behavior and can be empirically modeled remarkably well by a biexponential function. The current results provide a framework for interpreting experimental MR data on various phenoma, including water diffusion in giant axons, metabolite diffusion in the brain, and hyperpolarized gas diffusion in lung airways. Magn Reson Med 50:735–742, 2003.