Improved SNR in linear reordered 2D bSSFP imaging using variable flip angles
Improved SNR in linear reordered 2D bSSFP imaging using variable flip angles
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DOI：
10.1016/j.mri.2009.01.021
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发表时间：
2009-09-01
影响因子：
2.5
通讯作者：
Zaitsev, Maxim
中科院分区：
文献类型：
--
作者：
Paul, Dominik;Zaitsev, Maxim
本文提出了一种用于平衡稳态自由进动（bSSFP）成像的可变翻转角方法，该方法可以增加信噪比（SNR）和对比噪声比（CNR），同时保持特定吸收率（SAR）恒定或降低给定CNR和SNR的SAR。信噪比的增益是通过利用瞬态相位的高信号来实现的。利用M阶（斜坡长度）的三角函数实现了回波序列中翻转角的变化。变异与线性k空间重排序相结合，使得k空间的外部部分使用较低的翻转角alpha（min）进行采样，而k空间的中心部分使用较高的翻转角alpha（max）获得。在数据采集之前没有额外的准备或虚拟周期。考虑了不同起始翻转角alpha（min）和坡道长度M的几种变化方案。例如，使用alpha(min)=1度，M=96, alpha（max）可以设置为47度，而不会超过3 T时的SAR限制，并获得高达50%的信噪比，而通常，alpha=34度是最大可能的翻转角。在志愿者成像中，分辨率似乎不受影响。在所有情况下，没有观察到由于翻转角度变化引起的瞬态伪影。本文演示了在bSSFP中使用翻转角变化来提高信噪比和CNR，同时保持SAR恒定，这在高场强下尤其重要。翻转角度变化也可以与其他方法相结合，如平行成像技术，以进一步降低SAR。爱思唯尔公司2009年版权所有版权所有。
This article presents a variable flip-angle approach for balanced steady-state free precession (bSSFP) imaging, which allows increases in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) while keeping specific absorption rate (SAR) constant or reduces SAR for given CNR and SNR. The gain in SNR is achieved by utilizing the higher signal in the transient phase. Flip-angle variation during the echo train is realized using a trigonometric function with M steps (ramp length). Variation is combined with a linear k-space reordering such that outer parts of k-space are sampled using a lower flip angle alpha(min), while the central part of k-space is acquired with a higher flip angle alpha(max). No additional preparation or dummy cycles are applied prior to data acquisition. Several variation schemes with different starting flip angles alpha(min) and ramp length M are considered. For example, using alpha(min)=1 degrees and M=96, alpha(max) can be set to 47 degrees without exceeding SAR limits at 3 T and gaining up to 50% in SNR, while, conventionally, alpha=34 degrees is the maximal possible flip angle. Resolution seems unaffected in volunteer imaging. In all cases, no transient artifacts due to flip-angle variation were observed. This article demonstrates the use of flip-angle variations in bSSFP to increase SNR and CNR while keeping SAR constant, which is especially important at higher field strengths. Flip-angle variation can also be combined with other methods such as parallel imaging techniques for further SAR reduction. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.