Lee Yoojin, Callaghan Martina F, Nagy Zoltan
Laboratory for Social and Neural Systems Research, University of ZürichZürich, Switzerland; Department of Information Technology and Electrical Engineering, Institute of Biomedical Engineering, ETH ZürichZürich, Switzerland.
Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
Front Neurosci. 2017 Mar 9;11:106. doi: 10.3389/fnins.2017.00106. eCollection 2017.
In magnetic resonance imaging, precise measurements of longitudinal relaxation time () is crucial to acquire useful information that is applicable to numerous clinical and neuroscience applications. In this work, we investigated the precision of relaxation time as measured using the variable flip angle method with emphasis on the noise propagated from radiofrequency transmit field ([Formula: see text]) measurements. The analytical solution for precision was derived by standard error propagation methods incorporating the noise from the three input sources: two spoiled gradient echo (SPGR) images and a [Formula: see text] map. Repeated experiments were performed to estimate the total variance in maps and we compared these experimentally obtained values with the theoretical predictions to validate the established theoretical framework. Both the analytical and experimental results showed that variance in the [Formula: see text] map propagated comparable noise levels into the maps as either of the two SPGR images. Improving precision of the [Formula: see text] measurements significantly reduced the variance in the estimated map. The variance estimated from the repeatedly measured maps agreed well with the theoretically-calculated variance in estimates, thus validating the analytical framework for realistic experiments. We concluded that for mapping experiments, the error propagated from the [Formula: see text] map must be considered. Optimizing the SPGR signals while neglecting to improve the precision of the [Formula: see text] map may result in grossly overestimating the precision of the estimated values.
在磁共振成像中，精确测量纵向弛豫时间（）对于获取适用于众多临床和神经科学应用的有用信息至关重要。在这项工作中，我们研究了使用可变翻转角方法测量弛豫时间的精度，重点关注从射频发射场（[公式：见正文]）测量中传播的噪声。通过标准误差传播方法，结合来自三个输入源的噪声：两幅扰相梯度回波（SPGR）图像和一幅[公式：见正文]图，推导出弛豫时间精度的解析解。进行了多次弛豫时间实验，以估计弛豫时间图中的总方差，并将这些实验获得的值与理论预测值进行比较，以验证所建立的理论框架。分析和实验结果均表明，[公式：见正文]图中的方差向弛豫时间图中传播的噪声水平与两幅SPGR图像中的任何一幅相当。提高[公式：见正文]测量的精度可显著降低估计的弛豫时间图中的方差。从重复测量的弛豫时间图估计的方差与弛豫时间估计值的理论计算方差吻合良好，从而验证了实际弛豫时间实验的分析框架。我们得出结论，对于弛豫时间映射实验，必须考虑从[公式：见正文]图传播的误差。在忽略提高[公式：见正文]图精度的同时优化SPGR信号可能会导致严重高估估计的弛豫时间值的精度。
