Increased SNR and Reduced Distortions by Averaging Multiple Gradient Echo Signals in 3D FLASH Imaging of the Human Brain at 3T
Increased SNR and Reduced Distortions by Averaging Multiple Gradient Echo Signals in 3D FLASH Imaging of the Human Brain at 3T
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DOI：
10.1002/jmri.21629
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发表时间：
2009-01-01
影响因子：
4.4
通讯作者：
Dechent, Peter
中科院分区：
文献类型：
--
作者：
Helms, Gunther;Dechent, Peter
目的：演示多个梯度回波的平均如何改善人脑的高分辨率 FLASH（快速低角度拍摄）磁共振成像 (MRI)。材料和方法：通过模拟和在 3T 人脑上的三个实验来研究具有多个双极回波的 3D-FLASH。首先，重复时间（TR）增加了翻转角的平方，以保持理论推导的对比度。然后，回波数量以恒定 TR 增加，带宽在 11.0 至 1370 Hz/像素之间。最后，连续对 12 个回波采集序列（回波时间 4.9-59 毫秒）的信号进行平均，以研究 SNR 的增加。结果：在对比度不变的情况下，信号随翻转角和 sqrt(TR) 成比例增加。增加带宽可以改善基底皮层和血管的轮廓，而信噪比 (SNR) 的大部分损失可以通过平均来恢复。连续平均增加了 SNR，以在大致对应于 T-2* 的回波序列长度处达到最大效率。结论：通过获取额外的回波并增加 TR（并相应地增加翻转角以保持对比度），直到平均信号中相关的 T-2* 损失消耗了稳定状态下的 sqrt(TR) 增加，可以有效地获得 SNR。建议使用 350 Hz/像素或更高的带宽以及短于 T-2* 的回波序列。
Purpose: To demonstrate how averaging of multiple gradient echoes can improve high-resolution FLASH (fast low angle shot) magnetic resonance imaging (MRI) of the human brain.Materials and Methods: 3D-FLASH with multiple bipolar echoes was studied by simulation and in three experiments on human brain at 3T. First, the repetition time (TR) was increased by the square of the flip angle to maintain contrast as derived by theory. Then the number of echoes was increased at constant TR with bandwidths between 11.0 and 1370 Hz/pixel. Finally, signals of a 12-echo acquisition train (echo times 4.9-59 msec) were averaged consecutively to study the increase in SNR.Results: At unchanged contrast, the signal increased proportionally with flip angle and sqrt(TR). Increasing the bandwidth improved delineation of the basal cortex and vessels, while most of the loss in the signal-to-noise ratio (SNR) was recovered by averaging. Consecutive averaging increased the SNR to reach maximum efficiency at an echo train length corresponding roughly to T-2*.Conclusion: SNR is gained efficiently by acquiring additional echoes and increasing TR (and flip angle accordingly to maintain contrast) until the associated T-2* loss in the averaged signal consumes the sqrt(TR) increase in the steady state. A bandwidth of 350 Hz/pixel or higher and echo trains shorter than T-2* are recommended.