Assessment and correction of B1-induced errors in magnetization transfer ratio measurements
Assessment and correction of B1-induced errors in magnetization transfer ratio measurements
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DOI：
10.1002/mrm.20310
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发表时间：
2005-01-01
影响因子：
3.3
通讯作者：
Fazekas, F
中科院分区：
文献类型：
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作者：
Ropele, S;Filippi, M;Fazekas, F
磁化传递比（MTR）与饱和脉冲的场强（B-1）密切相关。因此，B-1变异可能导致显著的MTR变异，并可能影响直方图分析，特别是如果包括来自感兴趣的大体积的数据。进行了一项多中心研究，以确定健康志愿者脑组织中B-1错误的典型范围和相应的MTR变化。每家临床试验机构入组7例受试者，共28例受试者。此外，进行了数值模拟，以研究这种关系更普遍的脉冲饱和。从理论和经验上都可以证明，对于典型的B-1误差，在B-1误差和相应的MTR变化之间存在线性关系。此外，对于质子密度加权序列，这种关系似乎在很大程度上是独立的基本弛豫性质。整个大脑的平均B-1误差通常在-3%至-7%之间。由于不同的线圈特性，观察到不同扫描仪和部位之间存在显著的MTR差异。使用基于MTR和B-1数据之间的线性回归分析的简单校正方案，有可能将受试者间的变异减少约50%。此外，可以减少扫描仪间的变化，使得不能检测到扫描仪之间的显著差异。当在单中心或多中心研究中将MTR作为结局指标时，校正方案可能有用。(C)2004 Wiley-Liss，Inc.
The magnetization transfer ratio (MTR) is strongly related to the field strength (B-1) of the saturation pulse. B-1 variations therefore can result in significant MTR variations and can affect histogram analysis, particularly if data from a large volume of interest are included. A multicenter study was performed to determine the typical range of B-1 errors and the corresponding MTR variations in brain tissue of healthy volunteers. Seven subjects were included at each center resulting in a total cohort of 28 subjects. Additionally, numerical simulations were done to study this relationship more generally for pulsed saturation. It could be demonstrated, both theoretically and empirically, that for typical B-1 errors there is a linear relationship between B-1 error and the corresponding MTR change. In addition, for proton density-weighted sequences, this relationship seems to be largely independent of the underlying relaxation properties. Mean B-1 errors in the entire brain were typically in the range between -3% and -7%. Due to different coil characteristics significant MTR differences between different scanners an sites were observed. Using a simple correction scheme that is based on a linear regression analysis between MTR and B-1 data it was possible to reduce the intersubject variation by similar to50%. Furthermore, interscanner variation could be reduced such that no significant differences between scanners could be detected. The correction scheme may be useful when investigating MTR as an outcome measure in single or multicenter studies. (C) 2004 Wiley-Liss, Inc.