基于AFI的快速发射场B_1^+成像方法

Rapid B_1^+ Mapping Based on Actual Flip-Angle Imaging

该文提出了一种基于实际翻转角成像(Actual Flip-angle Imaging,AFI)的快速发射场测量方法(Fast AFI,FAFI),将多次激发平面回波成像(Multi-shot Echo Planar Imaging,Multi-shot EPI)的采集方式运用于AFI发射场(B_1^+)测量中,充分利用AFI序列中采集的等待时间,高倍数加速了水模和人体头部、腹部及盆腔的发射场测量.该文在水模和人体(n=16)实验中,验证了采用FAFI序列得到的B_1^+测量结果与AFI结果的一致性.FAFI序列大幅加速了发射场测量,为实现动态B_1^+匀场(B_1^+shimming)和快速局部激发提供了高效的发射场测量方法.

We propose a fast B1^＋ mapping method （FAFI） based on actual flip-angle imaging （AFI）, in which the single-echo gradient echo （GRE） acquisition in the conventional AFI sequence is replaced by a multi-shot echo planar imaging （Multi-shot EPI） acquisition. FAFI makes full use of the waiting time, and thus has greatly increased imaging speed. We evaluated the performance of FAFI on phantoms and human subjects （n=16）, and compared the results with those obtained using the conventional AFI method. It was demonstrated that it was possible to achieve high acceleration factor with FAFI, while preserving good consistency with the conventional AFI results. FAFI provides a powerful tool for dynamic B1^＋ mapping, and may find applications in dynamic B1^＋ shimming and rapid spatially selective radio frequency （RF） excitation.