Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.
High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
Magn Reson Med. 2018 Feb;79(2):1116-1126. doi: 10.1002/mrm.26704. Epub 2017 Apr 10.
In this work, 22 configurations for remote radiofrequency (RF) coil arrays consisting of different transmit element designs for 7 Tesla (T) ultrahigh-field MRI are compared by numerical simulations.
Investigated transmit RF element types are rectangular loops, micro striplines, micro striplines with meanders, 250-mm shielded dipoles with meanders, and lambda over two dipoles with and without shield. These elements are combined in four different configurations of circumferential RF body arrays with four or eight transmit elements each. Comparisons included coupling behavior, degrees of freedom offered by the individual transmit patterns, and metrics like power and specific absorption rate efficiency.
Coupling between neighboring RF elements is elevated (up to -7 dB) for all arrays with eight elements, whereas it is below -25 dB for arrays with only four elements. The cumulative sum of singular values points out highest degrees of freedom for the central transversal, reduced values in the central coronal, and minimum values in the sagittal slice. Concerning power and SAR efficiency, eight lambda over two dipoles are most advantageous.
Among the investigated remote arrays and parameters, a combination of eight dipoles appears to be most favorable for potential use in 7T body MRI. Magn Reson Med 79:1116-1126, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
在这项工作中，通过数值模拟比较了由用于 7 特斯拉（T）超高场 MRI 的不同发射元件设计组成的 22 种远程射频（RF）线圈阵列配置。
研究的发射 RF 元件类型为矩形环、微带线、带有曲折的微带线、带有曲折的 250mm 屏蔽偶极子以及带有和不带有屏蔽的 λ 双极子。这些元件以每四个或八个发射元件的四个不同的圆周 RF 体阵列配置组合在一起。比较包括耦合行为、各个发射模式提供的自由度以及功率和比吸收率效率等指标。
对于所有具有 8 个元件的阵列，相邻 RF 元件之间的耦合增强（高达-7dB），而对于只有 4 个元件的阵列，耦合则低于-25dB。奇异值的累积和指出了中间横切面的自由度最高，中间冠状面的自由度降低，矢状面的自由度最小。关于功率和 SAR 效率，8 个 λ 双极子最有利。
在所研究的远程阵列和参数中，8 个偶极子的组合似乎最有利于在 7T 体部 MRI 中使用。磁共振医学 79：1116-1126，2018。© 2017 年国际磁共振医学学会。
