Effects of slow flow on slice profile and NMR signal in fast imaging sequences.

A computer program has been developed to evaluate the selective-slice profiles obtained in the steady state for fast gradient-echo imaging. Both spoiled and refocused gradient-echo pulse sequences have been considered. By numerically solving the Bloch equations modified for the effects of flow, for a three-dimensional volume of spins, for realistic RF excitations and linear gradient combinations, the program permits the combined effects of flow and imaging variables on the magnetization slice profile to be assessed quantitatively. We have found that the gradient pattern in gradient-echo pulse sequences is a significant factor for determining the steady-state slice profiles and the strength of the NMR signal from the flowing spins.