STEAM-Burst: a single-shot, multi-slice imaging sequence without rapid gradient switching.
The stimulated-echo acquisition mode-Burst sequence is a single-shot, multi-slice imaging technique that does not involve rapid gradient switching. A Burst excitation pulse train is followed by a 90 degrees hard pulse and, after a mixing time, by a 90 degrees slice-selective pulse. A read gradient refocuses a set of stimulated echoes, which can be phase-encoded to form an image. By repeating the selective pulse N times, each time with the carrier frequency offset differently, it is possible to sample N slices in a single-shot. A comparison is made of the sequence with other three-dimensional single-shot methods. Experiments implementing the technique on a 3 T whole-body imaging system and a 2 T, 31-cm bore animal imager are described. Both phantom and brain images are presented. The principal advantages of the new sequence are its speed, the absence of rapid gradient switching and corresponding freedom from artifacts, its insensitivity to static magnetic field inhomogeneities, and its low acoustic noise. The main disadvantages are the low signal-to-noise ratio of the images produced and the concomitant limitation in resolution.