Hybrid sequences (spin echo + gradient echo)
|Type of sequence||Philips||Siemens||GE||Hitachi||Toshiba|
|Hybrid echo||GRASE||TGSE||Hybrid EPI|
These sequences are a mixture of fast spin echo techniques (using 180° rephasing pulses to create a spin echo train) and gradient echo (readout of several gradient echos between each 180° pulse).
During a single TR, several gradient echo trains are recorded, with a signal weighting of the spin echo type. Each echo has a different phase encoding to fill the k-space faster. The advantage of using intermediary gradient echos rather than spin echos (as in ultrafast spin echo sequences) is to reduce the number of 180° rephasing pulses, thereby reducing the quantity of radiofrequency energy deposited.