Ibrahim T S, Lee R, Baertlein B A, Abduljalil A M, Zhu H, Robitaille P M
Department of Radiology, The Ohio State University, Columbus, Ohio 43210, USA.
Magn Reson Imaging. 2001 Dec;19(10):1339-47. doi: 10.1016/s0730-725x(01)00404-0.
In this work, computational methods were utilized to optimize the field produced by the transverse electromagnetic (TEM) resonator in the presence of the human head at 8 Tesla. Optimization was achieved through the use of the classical finite difference time domain (FDTD) method and a TEM resonator loaded with an anatomically detailed human head model with a resolution of 2 mm x 2 mm x 2 mm. The head model was developed from 3D MR images. To account for the electromagnetic interactions between the coil and the tissue, the coil and the head were treated as a single system at all the steps of the model including, numerical tuning and excitation. In addition to 2, 3, 4, 6, and 10-port excitations, an antenna array concept was utilized by driving all the possible ports (24) of a 24-strut TEM resonator. The results show that significant improvement in the circularly polarized component of the transverse magnetic field could be obtained when using multiple ports and variable phase and fixed magnitude, or variable phase and variable magnitude excitations.
在这项工作中,利用计算方法对8特斯拉下人体头部存在时横向电磁(TEM)谐振器产生的场进行了优化。通过使用经典的时域有限差分(FDTD)方法以及加载有分辨率为2毫米×2毫米×2毫米的详细人体头部解剖模型的TEM谐振器实现了优化。头部模型由3D磁共振图像构建。为了考虑线圈与组织之间的电磁相互作用,在模型的所有步骤(包括数值调谐和激励)中,将线圈和头部视为一个单一系统。除了2、3、4、6和10端口激励外,还通过驱动24支柱TEM谐振器的所有可能端口(24个)采用了天线阵列概念。结果表明,当使用多端口以及可变相位和固定幅度或可变相位和可变幅度激励时,横向磁场的圆极化分量可得到显著改善。