Luo Minmin, Hu Can, Zhuang Yayun, Chen Wufan, Liu Feng, Xin Sherman Xuegang
Biomed Tech (Berl). 2016 Aug 1;61(4):455-61. doi: 10.1515/bmt-2015-0171.
The specific absorption rate (SAR) is an important issue to be considered in fetus MRI at 3 T due to the high radiofrequency energy deposited inside the body of pregnant woman. The high dielectric material (HDM) has shown its potential for enhancing B1 field and reducing SAR in MRI. The aim of this study is to assess the feasibility of SAR reduction by adding an HDM to the fetus MRI. The feasibility of SAR reduction is numerically assessed in this study, using a birdcage coil in transmission loaded with an electromagnetic pregnant woman model in the SEMCAD-EM solver. The HDMs with different geometric arrangements and dielectric constants are manually optimized. The B1+ ${B_1}^ + $ homogeneity is also considered while calculating the optimized fetus 10 g local SAR among different strategies in the application of HDM. The optimum maximum fetus 10 g local SAR was obtained as 2.25 W/kg, by using two conformal pads placed left and right with the dielectric constant to be 400, reduced by 24.75% compared to that without the HDM. It indicated that the SAR can be significantly reduced with strategic placement of the HDM and the use of HDM may provide a simple, effective and low-cost method for reducing the SAR for the fetus MRI at 3 T.
由于孕妇体内沉积的射频能量较高，比吸收率（SAR）是3T胎儿MRI中需要考虑的一个重要问题。高介电常数材料（HDM）已显示出其在增强B1场和降低MRI中SAR方面的潜力。本研究的目的是评估在胎儿MRI中添加HDM降低SAR的可行性。本研究使用SEMCAD-EM求解器中加载电磁孕妇模型的传输鸟笼线圈，对降低SAR的可行性进行了数值评估。对具有不同几何排列和介电常数的HDM进行了人工优化。在计算HDM应用中不同策略下优化后的胎儿10g局部SAR时，也考虑了B1+ ${B_1}^ + $ 均匀性。通过左右放置两个介电常数为400的共形垫，获得了最佳的最大胎儿10g局部SAR为2.25W/kg，与不使用HDM相比降低了24.75%。这表明，通过合理放置HDM可以显著降低SAR，并且使用HDM可能为降低3T胎儿MRI的SAR提供一种简单、有效且低成本的方法。
