A MULTIPLE-NARROW-PULSE APPROXIMATION FOR RESTRICTED DIFFUSION IN A TIME-VARYING FIELD GRADIENT

Analytical expressions for the NMR signal of an ensemble of spins diff using in a bounded medium in the presence of a magnetic field gradient exist only in the limit of gradient pulses so short that no diffusion takes place during them, The temporal behavior of any gradient pulse is approximated by a sum of impulses, each being in the narrow-gradien t-pulse limit. This approximate, analytical solution for the echo atte nuation due to restricted diffusion between two parallel plates with r eflecting boundaries in the presence of nonnarrow gradient pulses agre es with that from numerical simulations by Blees [J. Magn. Reson. A 10 9, 203 (1994)]. (C) 1996 Academic Press, Inc.