Multiecho sequences with variable refocusing flip angles: Optimization of signal behavior using smooth transitions between pseudo steady states (TRAPS)
Multiecho sequences with variable refocusing flip angles: Optimization of signal behavior using smooth transitions between pseudo steady states (TRAPS)
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DOI：
10.1002/mrm.10391
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发表时间：
2003-03-01
影响因子：
3.3
通讯作者：
Scheffler, K
中科院分区：
文献类型：
--
作者：
Hennig, J;Weigel, M;Scheffler, K
介绍了一种弛豫增强快速采集（RARE）序列（也称为快速自旋回波（TSE）或快速自旋回波（FSE））的变体。该技术使用沿回波链的可变翻转角沿着，使得磁化最初准备为低重聚焦翻转角（α <180度）的静态伪稳态（PSS）。结果表明，这样的准备后，磁化将始终保持非常接近的静态PSS，即使在随后的重聚焦翻转角的显着变化。这允许TSE序列的设计，其中产生100%可获得信号的高重聚焦翻转角仅应用于k空间中心的重要回波编码。它表明，减少的RF功率（RFP）的2.5-6倍，可以实现没有任何损失的信号强度。受激回波路径的贡献导致有效TE减小因子f（t），对于典型的实现方式，该因子f（t）在0.5-0.8的量级上。这允许使用更长的回波读出时间，并且因此使用更长的回波串，用于以给定的T-2对比度采集图像。(C)2003 Wiley-Liss，Inc.
A variation of the rapid acquisition with relaxation enhancement (RARE) sequence (also called turbo spin-echo (TSE) or fast spin-echo (FSE)) is presented. This technique uses variable flip angles along the echo train such that magnetization is initially prepared into the static pseudo steady state (PSS) for a low refocusing flip angle (alpha < 180degrees). It is shown that after such a preparation, magnetization will always stay very close to the static PSS even after significant variation of the subsequent refocusing flip angles. This allows the design of TSE sequences in which high refocusing flip angles yielding 100% of the attainable signal are applied only for the important echoes encoding for the center of k-space. It is demonstrated that a reduction of the RF power (RFP) by a factor of 2.5-6 can be achieved without any loss in signal intensity. The contribution of stimulated-echo pathways leads to a reduction of the effective TE by a factor f(t), which for typical implementations is on the order of 0.5-0.8. This allows the use of longer echo readout times, and thus longer echo trains, for acquiring images with a given T-2 contrast. (C) 2003 Wiley-Liss, Inc.