Refocused (Steady State) Gradient Echo

24 Refocused (Steady State) Gradient Echo

Another way to use gradient echo technique (GRE) is shown in Fig. 24.1. A refocused, rewound, or coherent gradient echo sequence incorporates free induction decay (FID) and spin echo attributes. Excitation, phase encoding, and readout for a refocused GRE sequence are identical to that for a spoiled GRE sequence, as discussed in Case 23. However, rather than destroy or spoil the transverse magnetization, the objective with this approach is for the transverse magnetization to remain transverse and (partially) coherent across two TR intervals, creating a spin echo (SE) from the two successive RF pulses that contributes to the signal ultimately acquired and encoded. To accomplish this, a phase-encoding gradient of the opposite sign to the first phase-encoding gradient is added after readout (Fig. 24.1

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