Ultrafast spoiled gradient echo sequences
|Type of sequence||Philips||Siemens||GE||Hitachi||Toshiba|
|Ultrafast spoiled GE|| |
Ultrafast spoiled GE|
with magnetization preparation
Ultrafast gradient echo sequences use a small flip angle, a very short TR and optimized k-space filling to reduce acquisition time (to roughly one second per slice). The drawback of a small flip angle and very short TR is poor T1-weighting.
To preserve T1 contrast, a 180° inversion pulse prepares magnetization before repetitions of the ultrafast gradient echo imagery sequence . Effective inversion time will correspond to the delay between the inversion pulse and acquisition of the central k-space lines.
To obtain T2-weighting, the preparatory pattern is of the spin echo type (90° - 180°) so that the ultrafast GE imaging sequence can start with longitudinal magnetization whose amplitude depends on T2 .
K-space filling can follow variable trajectories (linear, centripetal, centrifugal) to determine image contrast. Either all the k-space lines are acquired after a single inversion pulse (« single shot »), or only a group of lines is acquired (segmented filling).
The speed of these T1-weighted gradient echo sequences is particularly suited to monitoring Gadolinium bolus arrival in imaging at arterial phase and in T1 high resolution 3D imaging.