Liberman Gilad, Louzoun Yoram, Ben Bashat Dafna
The Functional Brain Center The Wohl Institute for Advanced Imaging, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel; Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan, Israel.
J Magn Reson Imaging. 2014 Jul;40(1):171-80. doi: 10.1002/jmri.24373. Epub 2013 Nov 25.
To improve the calculation of T1 relaxation time from a set of variable flip-angle (FA) spoiled gradient recalled echo images.
The proposed method: (a) uses a uniform weighting of all FAs, (b) takes into account global inaccuracies in the generation of the prescribed FAs by estimating the actual FAs, and (c) incorporates data-driven local B1 inhomogeneity corrections. The method was validated and its accuracy tested using simulated data, phantom, and in vivo experiments. Results were compared with existing analysis methods and to inversion recovery (IR). Consistency was assessed by means of repeated scans of two subjects. Reference values were obtained from eight healthy subjects from various brain regions and compared with literature values.
The method accurately and consistently estimated T1 values in all cases. The method was more robust, in comparison with the standard method, to the choice of FA set; to inaccuracies in generation of the prescribed FAs (in simulated data, T1 estimation error was 12.1 ms versus 235.5 ms); demonstrated greater consistency (in vivo study showed interscan T1 difference of 80 ms versus 356 ms); and achieved a better agreement with IR on phantom (median absolute difference of 123.8 ms versus 790 ms). Reference T1 values were 883/801 ms for female/male in white matter and 1501/1349 ms in gray matter, within the range previously reported.
The proposed method overcomes some inaccuracies in FA production, providing more accurate estimation of T1 values compared with standard methods, and is applicable for currently available data.
改进从一组可变翻转角（FA）扰相梯度回波图像计算T1弛豫时间的方法。
所提出的方法：（a）对所有翻转角采用均匀加权，（b）通过估计实际翻转角来考虑规定翻转角生成中的全局误差，以及（c）纳入数据驱动的局部B1不均匀性校正。该方法通过模拟数据、体模和体内实验进行验证并测试其准确性。将结果与现有分析方法以及反转恢复（IR）进行比较。通过对两名受试者的重复扫描评估一致性。从八名健康受试者的不同脑区获得参考值，并与文献值进行比较。
该方法在所有情况下均能准确且一致地估计T1值。与标准方法相比，该方法对翻转角集的选择更具鲁棒性；对规定翻转角生成中的误差更具鲁棒性（在模拟数据中，T1估计误差为12.1毫秒，而标准方法为235.5毫秒）；表现出更高的一致性（体内研究显示扫描间T1差异为80毫秒，而标准方法为356毫秒）；并且在体模上与IR的一致性更好（中位数绝对差异为123.8毫秒，而标准方法为790毫秒）。白质中女性/男性的参考T1值分别为883/801毫秒，灰质中为1501/1349毫秒，在先前报道的范围内。
所提出的方法克服了翻转角产生中的一些误差，与标准方法相比能更准确地估计T1值，并且适用于当前可用的数据。
