Abraham Roney, Ibrahim Tamer S
School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma, USA.
Magn Reson Med. 2007 Feb;57(2):235-42. doi: 10.1002/mrm.21139.
In this article, a radiofrequency (RF) excitation scheme for 7-Tesla (T) whole-body applications is derived and analyzed using the finite difference time domain (FDTD) method. Important features of the proposed excitation scheme and coil (a potential 7T whole-body transverse electromagnetic [TEM] resonator design), from both operational and electromagnetic perspectives, are discussed. The choice of the coil's operational mode is unconventional; instead of the typical "homogenous mode," we use a mode that provides a null field in the center of the coil at low-field applications. Using a 3D FDTD implementation of Maxwell's equations, we demonstrate that the whole-body 7T TEM coil (tuned to the aforementioned unconventional mode and excited in an optimized near-field, phased-array fashion) can potentially provide 1) homogenous whole-slice (demonstrated in three axial, sagittal, and coronal slices) and 2) 3D localized (demonstrated in the heart) excitations. As RF power was not considered as a part of the optimization in several cases, the significant improvements achieved by whole-slice RF excitation came at the cost of considerable increases in RF power requirements.
在本文中，使用时域有限差分（FDTD）方法推导并分析了一种用于7特斯拉（T）全身应用的射频（RF）激励方案。从操作和电磁角度讨论了所提出的激励方案和线圈（一种潜在的7T全身横向电磁[TEM]谐振器设计）的重要特性。线圈操作模式的选择是非传统的；在低场应用中，我们不是使用典型的“均匀模式”，而是使用一种在线圈中心提供零场的模式。通过麦克斯韦方程组的三维FDTD实现，我们证明了全身7T TEM线圈（调谐到上述非传统模式并以优化的近场相控阵方式激励）有可能提供1）均匀的全切片（在三个轴向、矢状和冠状切片中得到证明）和2）三维局部（在心脏中得到证明）激励。由于在几种情况下未将射频功率视为优化的一部分，全切片射频激励所实现的显著改进是以射频功率需求的大幅增加为代价的。
