Evaluation of non-selective refocusing pulses for 7 T MRI.
Evaluation of non-selective refocusing pulses for 7 T MRI.
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DOI：
10.1016/j.jmr.2011.11.010
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发表时间：
2012-01
影响因子：
2.2
通讯作者：
Gore, John C.
中科院分区：
文献类型：
--
作者：
Moore, Jay;Jankiewicz, Marcin;Anderson, Adam W.;Gore, John C.
关键词：
持续需要在超高场(≥7T)人类核磁共振的背景下实现适当重聚焦的改进的RF脉冲。简单的块或正弦脉冲非常容易受到射频场不均匀的影响，而绝热脉冲通常被认为在7T时太过SAR密集而不能实际使用。然而，落在这些极端之间的脉冲阵列的性能还没有被系统地评估。这项工作的目的是比较21种非选择性重新聚焦脉冲的性能，这些脉冲跨越了一系列持续时间和SAR水平。这项评估是基于模拟以及在7 T进行的体模和活体人脑实验。测试的重新聚焦设计包括块、复合块、BIR-4、双曲正割和数值优化的复合波形。这些脉冲被分成三个合成孔径雷达类别和两个持续时间类别，并基于3-D自旋回波序列中的信号增益，在每一类别中提出了实用的使用建议。发现所有评估的脉冲相对于180°阻断脉冲产生更大的体积平均信号。虽然信号增益通常伴随着增加的合成孔径雷达或持续时间的代价，但一些脉冲被发现导致显著的信号增强，同时也遵守实际限制。这项工作展示了单通道重聚焦脉冲设计可实现的信号增益和损耗，并有助于选择合适的重聚焦脉冲以用于7T下的实际三维自旋回波成像。它进一步建立了一个参考，可以与未来的脉冲和多通道设计进行比较。
There is a continuing need for improved RF pulses that achieve proper refocusing in the context of ultra-high field (≥ 7 T) human MRI. Simple block or sinc pulses are highly susceptible to RF field inhomogeneities, and adiabatic pulses are generally considered too SAR intensive for practical use at 7 T. The performance of the array of pulses falling between these extremes, however, has not been systematically evaluated. The aim of this work was to compare the performances of 21 non-selective refocusing pulses spanning a range of durations and SAR levels. The evaluation was based upon simulations and both phantom and in vivo human brain experiments conducted at 7 T. Tested refocusing designs included block, composite block, BIR-4, hyperbolic secant, and numerically optimized composite waveforms. These pulses were divided into three SAR classes and two duration categories, and, based on signal gain in a 3-D spin echo sequence, practical recommendations on usage are made within each category. All evaluated pulses were found to produce greater volume-averaged signals relative to a 180° block pulse. Although signal gains often come with the price of increased SAR or duration, some pulses were found to result in significant signal enhancement while also adhering to practical constraints. This work demonstrates the signal gains and losses realizable with single-channel refocusing pulse designs and should assist in the selection of suitable refocusing pulses for practical 3-D spin-echo imaging at 7 T. It further establishes a reference against which future pulses and multi-channel designs can be compared.
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影响因子：
3.3
作者：
CONOLLY, S;GLOVER, G;MACOVSKI, A
通讯作者：
MACOVSKI, A
影响因子：
3.3
作者：
HORNAK, JP;SZUMOWSKI, J;BRYANT, RG
通讯作者：
BRYANT, RG
影响因子：
3.3
作者：
Ordidge, RJ;Wylezinska, M;Franconi, F
通讯作者：
Franconi, F
影响因子：
3.3
作者：
JEZZARD, P;BALABAN, RS
通讯作者：
BALABAN, RS
影响因子：
2.2
作者：
Moore, Jay;Jankiewicz, Marcin;Gore, John C.
通讯作者：
Gore, John C.