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MRI Sequences

Hybrid sequences (spin echo + gradient echo)

by Denis Hoa

Type of sequence Philips Siemens GE Hitachi Toshiba
Hybrid echo GRASE TGSE Hybrid EPI

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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.