Improving peak local SAR prediction in parallel transmit using in situ S-matrix measurements
Improving peak local SAR prediction in parallel transmit using in situ S-matrix measurements
复制标题
DOI：
10.1002/mrm.26261
复制
发表时间：
2017-05-01
影响因子：
3.3
通讯作者：
Hoogduin, Hans
中科院分区：
文献类型：
--
作者：
Restivo, Matthew;Raaijmakers, Alexander;Hoogduin, Hans
目的局部比吸收峰值率（pSAR 10 g）是射频传输过程中判断患者安全性的重要参数。并行发射MRI的pSAR 10 g预测受模拟环境中建模阵列所表现出的耦合水平的影响。然而，模拟阵列耦合很少等于物理阵列耦合。准确地模拟物理阵列耦合可以提高预测SAR levels.MethodsThe散射参数矩阵（S-矩阵）的原型4通道阵列的准确性进行了测量，在原位使用定向耦合器安装在一个7 T扫描仪。协议之间的模拟和测量的S-矩阵实现了通过使用网络协同仿真与修改的成本函数。B1+地图中获得的幻影进行了比较，B1+分布从simulation.ResultsThe修改后的共同模拟技术迫使模拟有S-矩阵类似的测量值。现实与理想模拟耦合条件的比较表明，理想模拟耦合可能导致pSAR 10 g预测的较大（>40%）误差，即使在阵列合理调整时也是如此。模拟的B1+分布匹配测量的B1+分布更好的耦合时，准确simulated.ConclusionConsidering在数值模拟中的测量阵列耦合矩阵消除了潜在的混淆pSAR 10 g预测。Magn Reson Med 77：2040-2047，2017。(c)2016年国际医学磁共振学会
PurposePeak local specific absorption rate (pSAR10g) is an important parameter used to determine patient safety during radiofrequency transmission. pSAR10g predictions for parallel transmit MRI are affected by the level of coupling exhibited by a modeled array in the simulation environment. However, simulated array coupling is rarely equal to the physical array coupling. Accurately simulating the physical array coupling may improve the accuracy of predicted SAR levels.MethodsThe scattering parameter matrix (S-matrix) of a prototype 4-channel array was measured in situ using directional couplers installed on a 7T scanner. Agreement between the simulated and measured S-matrix was achieved by using network co-simulation with a modified cost function. B1+ maps acquired in a phantom were compared to B1+ distributions determined from simulations.ResultsThe modified co-simulation technique forces the simulations to have S-matrices similar to the measured values. A comparison of realistically versus ideally simulated coupling conditions shows that ideally simulated coupling can result in large (>40%) error in pSAR10g predictions, even when the array is reasonably tuned. The simulated B1+ distributions match the measured B1+ distributions better when the coupling is accurately simulated.ConclusionConsidering the measured array coupling matrix in numerical simulations eliminates a potential confound in pSAR10g prediction. Magn Reson Med 77:2040-2047, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine