Xu Dan, King Kevin F, Zhu Yudong, McKinnon Graeme C, Liang Zhi-Pei
Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Magn Reson Med. 2007 Aug;58(2):326-34. doi: 10.1002/mrm.21314.
Recently, theoretical and experimental work has shown that parallel transmission of RF pulses can be used to shorten the duration of multidimensional spatially-selective pulses and compensate for B(1) field inhomogeneity. However, all the existing noniterative methods can design only excitation pulses for parallel transmission with a small flip angle (e.g., 30 degrees , or at most 90 degrees ) and cannot design large-tip-angle inversion/refocusing pulses, because these methods are based on the small-tip-angle (STA) approximation of the Bloch equation. In this work, a method to design large-tip-angle multidimensional spatially-selective pulses for parallel transmission is proposed, based on an extension of the single-channel linear-class large-tip-angle (LCLTA) theory. Design examples of 2D refocusing and inversion parallel transmit pulses and magnetization profiles from Bloch equation simulations demonstrate the strength of the proposed method. A 2D spin-echo parallel transmission experiment on a slab phantom using a 180 degrees refocusing pulse with an eight-channel transmit-only array further validates the effectiveness of the proposed method.
最近，理论和实验工作表明，射频脉冲的并行传输可用于缩短多维空间选择性脉冲的持续时间，并补偿B(1)场不均匀性。然而，所有现有的非迭代方法只能设计用于小翻转角（例如30度，或至多90度）并行传输的激发脉冲，而不能设计大翻转角的反转/重聚焦脉冲，因为这些方法基于布洛赫方程的小翻转角（STA）近似。在这项工作中，基于单通道线性类大翻转角（LCLTA）理论的扩展，提出了一种设计用于并行传输的大翻转角多维空间选择性脉冲的方法。二维重聚焦和反转并行发射脉冲的设计示例以及布洛赫方程模拟的磁化分布证明了所提出方法的优势。在平板模型上使用具有八通道仅发射阵列的180度重聚焦脉冲进行的二维自旋回波并行传输实验进一步验证了所提出方法的有效性。
