Balanced SSFP & Modifications for Unique Contrast

The term “steady state” refers to the equilibrium condition that evolves when magnetization experiences a train of radiofrequency (RF) pulses. If RF pulses are applied on the order of seconds (TR≈T1), the magnetization decays away completely in the transverse plane between RF pulses, but may not recover fully along the longitudinal axis. In the resulting steady state, the magnetization tipped away from the longitudinal axis by an RF pulse is exactly cancelled by recovery of magnetization along the longitudinal axis during the TR. However, “steady-state sequences” typically refer to a more specific case in which both T1 and T2 relaxation are interrupted by very rapid RF pulses (TR≤T2<T1). In this situation, there is residual transverse magnetization at the end of the TR that will be tipped by the subsequent RF pulse.