FIG 1. A, Diagram of the PSIF pulse sequence. p_n (the PSIF echo) is a spin echo that results from refocusing the echo f_n-1 by the RF pulse, n. f_n-1 (the FISP echo) is a gradient echo of the RF pulse, n-1, refocused by the readout gradient, G_r. Only the PSIF echoes are sampled with this sequence. This results in TE_eff > TR, with T_E(p) = 2T_R - T_E(f) in the symmetric arrangement of RF pulses and gradients shown. The phase-encoding gradients are applied before and after the echo (including a compensating pulse) for a zero net phase-encoding gradient between RF pulses to avoid affecting the established steady state. Data are sampled during the interpulse interval to avoid interference with RF transmission (6).

B, Alternating RF pulses and oscillating transverse magnetization in relation to the free induction decay (FID) and spin echo (SE) in SSFP imaging with the PSIF sequence.