THE INFLUENCE OF A NONCONSTANT MAGNETIC-FIELD GRADIENT ON PFG NMR DIFFUSION EXPERIMENTS - A BROWNIAN-DYNAMICS COMPUTER-SIMULATION STUDY

The influence of a nonconstant magnetic-field gradient on the performa nce of pulsed-held-gradient NMR diffusion experiments was investigated by performing Brownian-dynamics simulations for two different coil de signs using two different active sample volumes for each coil. The act ive sample volumes were chosen in order to represent different degrees of deviation from a perfectly constant magnetic-field gradient, The r esults show that one can actually tolerate a rather large deviation fr om a perfectly constant magnetic-field gradient and still obtain accur ate values of the selfdiffusion coefficients. The dependence of Delta (the observation time) and the dependence of D (the self-diffusion coe fficient) while keeping D and Delta constant, respectively, were also investigated for three of the active sample volumes. The simulations s how that the effects due to a nonconstant field gradient depend only s lightly on the values of Delta and D. In conclusion, the Brownian-dyna mics computer simulations procedure is a quantitative way of investiga ting the performance characteristics of a gradient coil of a certain d esign before it is built. (C) 1997 Academic Press.