Strongly modulating pulses for counteracting RF inhomogeneity at high fields
Strongly modulating pulses for counteracting RF inhomogeneity at high fields
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DOI：
10.1002/mrm.21700
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发表时间：
2008-09-01
影响因子：
3.3
通讯作者：
Amadon, A.
中科院分区：
文献类型：
--
作者：
Boulant, N.;Le Bihan, D.;Amadon, A.
报道了一种用于抵消高场射频不均匀性的新脉冲技术。脉冲利用体素 B-1 和 B-0 幅度二维直方图的详细知识，通过优化过程生成翻转角均匀的门。尽管迄今为止大多数方法都需要使用并行传输，但该方法不需要使用并行传输，因此具有多种优点。该算法确定照射方案所需的数据仅需要一次传输 B-1 以及 B-0 不均匀性测量。使用 B-1 和 B-0 幅度二维直方图而不是它们的空间分布也大大降低了优化问题的复杂性，使算法能够在不到 30 秒的时间内找到 RF 解决方案。最后，优化过程基于精确计算，不使用任何线性近似。在本文中，报告了该方法背后的理论以及用于 3D 脑成像的 3T 梯度回波实验数据。与使用扫描仪校准的标准方脉冲相比，获得的图像使翻转角正弦的标准偏差减少了所需值的 15 倍。
A new pulse technique for counteracting RF inhomogeneity at high fields is reported. The pulses make use of the detailed knowledge of the voxels' B-1 and B-0 amplitude 2D histogram to generate, through an optimization procedure, gates where the flip angle is made uniform. Although most approaches to date require the use of parallel transmission, this method does not and therefore offers several advantages. The data necessary for the algorithm to determine an irradiation scheme requires only one transmit B-1 along with a B-0 inhomogeneity measurement. The use of a B-1 and B-0 amplitude 2D histogram instead of their spatial distribution also decreases substantially the complexity of the optimization problem, allowing the algorithm to find an RF solution in less than 30 s. Finally, the optimization procedure is based on an exact calculation and does not use any linear approximation. In this article, the theory behind the method in addition to spoiled gradient echo experimental data at 3T for 3D brain imaging are reported. The images obtained yield a reduction of the standard deviation of the sine of the flip angle by a factor of up to 15 around the desired value, compared to when a standard square pulse calibrated by the scanner is used.