Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
Department of Radiology, University of Calgary, Calgary, AB, Canada; Child and Adolescent Imaging Research (CAIR) Program, Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.
J Neurosci Methods. 2018 Jun 1;303:86-94. doi: 10.1016/j.jneumeth.2018.02.012. Epub 2018 Feb 21.
The relationships between scan duration, signal-to-noise ratio (SNR) and sample size must be considered and understood to design optimal GABA-edited magnetic resonance spectroscopy (MRS) studies.
Simulations investigated the effects of signal averaging on SNR, measurement error and group-level variance against a known ground truth. Relative root mean square errors (measurement error) and coefficients of variation (group-level variance) were calculated. GABA-edited data from 18 participants acquired from five voxels were used to examine the relationships between scan duration, SNR and quantitative outcomes in vivo. These relationships were then used to determine the sample sizes required to observe different effect sizes.
In both simulated and in vivo data, SNR increased with the square root of the number of averages. Both measurement error and group-level variance were shown to follow an inverse-square-root function, indicating no significant impact of cumulative artifacts. Comparisons between the first two-thirds of the data and the full dataset showed no statistical difference in group-level variance. There was, however, some variability across the five voxels depending on SNR, which impacted the sample sizes needed to detect group differences in specific brain regions.
Typical scan durations can be reduced if taking into account a statistically acceptable amount of variance and the magnitudes of predicted effects.
While scan duration in GABA-edited MRS has typically been considered in terms of SNR, it is more appropriate to think in terms of the amount of measurement error and group-level variance that provides sufficient statistical power.
在设计最佳 GABA 编辑磁共振波谱（MRS）研究时，必须考虑并理解扫描时间、信噪比（SNR）和样本量之间的关系。
模拟研究了信号平均对 SNR、测量误差和组水平方差的影响，这些都是针对已知的真实情况进行的。计算了相对均方根误差（测量误差）和变异系数（组水平方差）。使用来自 18 名参与者的五个体素采集的 GABA 编辑数据，研究了扫描时间、SNR 和体内定量结果之间的关系。然后，使用这些关系来确定观察不同效果大小所需的样本量。
在模拟和体内数据中，SNR 随平均次数的平方根增加。测量误差和组水平方差都遵循平方根倒数函数，表明累积伪影没有显著影响。与全数据集相比，前两到三分之一样本数据的组水平方差没有统计学差异。然而，根据 SNR，五个体素之间存在一些差异，这会影响在特定脑区检测组间差异所需的样本量。
如果考虑到可接受的统计方差量和预测效应的幅度，可以减少典型的扫描时间。
虽然 GABA 编辑 MRS 中的扫描时间通常是根据 SNR 来考虑的，但更适合从提供足够统计功效的测量误差和组水平方差的量的角度来考虑。
