Single-shot pseudo-centric EPI for magnetization-prepared imaging.

ABSTRACT

PURPOSE: To implement a single-shot centric-reordered EPI (1sh-CenEPI), which reduces TE significantly, thus enabling to improve SNR for magnetization-prepared imaging. METHODS: We proposed a 1sh-CenEPI in which grouped oscillating readout gradients, phase-encoding blips within each group, and big phase-encoding jumps between two consecutive groups are incorporated to encode whole k-space from the center to the edges in a single shot. The concept was tested on phantoms and human brains at 3 T. In addition, the proposed reordering scheme was applied to pseudo-continuous arterial spin labeling for evaluating the efficiency of the centric reordering in magnetization-prepared imaging. RESULTS: The proposed 1sh-CenEPI reduced TE from 50 ms to 1.4 ms for gradient-echo EPI, and from 100 ms to 7 ms for spin-echo EPI, while the elongation of readout duration was below 10% of the whole readout duration in most cases. The 1sh-CenEPI images exhibited no distinct geometric distortion both in phantom and human brain, comparable to the conventional two-shot center-out EPI. In pseudo-continuous arterial spin labeling results, 3-fold temporal SNR increase and 2-fold spatial SNR increase in the perfusion-weighted images were achieved with 1sh-CenEPI compared with the conventional linear ordering, whereas the cerebral blood flow values were consistent with previous studies. CONCLUSION: The proposed 1sh-CenEPI significantly reduced TE while maintaining similar readout window and providing images comparable to the conventional linear and multishot center-out EPI images. It can be a qualified candidate as a new readout for various magnetization-prepared imaging techniques.