EFFECT OF DIFFUSION ON THE STEADY-STATE MAGNETIZATION WITH PULSED FIELD GRADIENTS

Steady-state free precession with pulsed field gradients in the presence of spin diffusion is investigated. The exact effect of diffusion on SSFP magnetization and its dependence on the pulsed field gradient amplitudes and timing, the relaxation and repetition times, and the flip angle are established theoretically. A relatively simple form is given for the average transverse magnetization when we assume that the precession angles within each voxel range from 0 to 2π uniformly, which is likely to be true in most imaging situations. Some illustrative numerical results are presented to show the different effects of diffusion in two common types of steady-state fast imaging pulse sequences: those which use the coherent transverse magnetization after the RF pulse as the signal for imaging and those which use the coherent magnetization just before the RF pulse for imaging. The magnitude of the effects calculated with this theoretical expression is compared with two approximate solutions proposed by other investigators. © 1990.