Some factors that influence the steady state in steady-state free precession

Steady-state free precession (SSFP) and particularly the spatially periodic magnetization response with wavelength lambda that results in the presence of an applied gradient is discussed. The maximum SSFP magnetization does not always occur at the Larmor frequency but rather depends on both the phase cycling of the rf pulses and on the rf tip angle. The slow flow sensitivity of SSFP also depends on lambda. Experimental data of the flow sensitivity is shown to be parameterized by a dimensionless dephasing parameter phi defined as the ratio of the distance traveled by a spin in one cycle of the SSFP sequence as compared to lambda. An example of the creation of a moving reference frame with the SSFP sequence is given. The modulation in image intensity that results when the gradients are nearly but not exactly compensated and lambda becomes large (i.e., tens of pixels long) is demonstrated. The pixel length must be an integral number of lambda's in order to have a uniform image intensity from a uniform phantom.