超高场7T MR成像下具有高通道间隔离度和B1效率的收发器阵列发夹RF谐振器
Hairpin RF Resonators for Transceiver Arrays with High Inter-channel Isolation and B1 Efficiency at Ultrahigh Field 7T MR Imaging
摘要：
要求紧密配合或高密度收发器RF阵列元件之间的电磁解耦以保持来自各个通道的磁通量密度的完整性，以增强检测灵敏度和并行成像的性能。高阻抗RF线圈已被证明是规避这些耦合问题的突出设计方法。然而，这些线圈的固有特性对B1场效率和SNR有影响。在这项工作中，我们提出了一个发夹高阻抗RF谐振器设计高度去耦多通道收发器阵列在双磁场。由于发夹谐振器的高阻抗特性，所提出的收发器阵列可以提供高解耦性能，而无需在谐振元件之间使用任何专用的解耦电路。由于消除了谐振器电路中的集总电感器，可以预期成像对象中的更高B1场效率。为了验证发卡式射频线圈的可行性，对线圈的去耦性能、场分布和信噪比进行了系统的研究，并将结果与现有的高阻抗射频线圈进行了比较，“自去耦RF线圈”。为了进一步研究其性能，设计了一个使用加载有圆柱形体模的拟议发夹谐振器的8通道头部线圈阵列，表明与7 T的“自去耦”线圈相比，B1+场强增加了19%。此外，发夹射频线圈的特性进行了评估，使用一个更现实的人体头部体素模型数值。与自去耦高阻抗线圈相比，所提出的发夹RF线圈提供了优异的去耦性能和优异的RF磁场效率。一对发夹线圈的实验结果与数值计算结果吻合较好。
英文摘要：
Electromagnetic decoupling among a close-fitting or high-density transceiver RF array elements is required to maintain the integrity of the magnetic flux density from individual channel for enhanced performance in detection sensitivity and parallel imaging. High-impedance RF coils have demonstrated to be a prominent design method to circumvent these coupling issues. Yet, inherent characteristics of these coils have ramification on the B1 field efficiency and SNR. In this work, we propose a hairpin high impedance RF resonator design for highly decoupled multichannel transceiver arrays at ultrahigh magnetic fields. Due to the high impedance property of the hairpin resonators, the proposed transceiver array can provide high decoupling performance without using any dedicated decoupling circuit among the resonant elements. Because of elimination of lumped inductors in the resonator circuit, higher B1 field efficiency in imaging subjects can be expected. In order to validate the feasibility of the proposed hairpin RF coils, systematical studies on decoupling performance, field distribution, and SNR are performed, and the results are compared with those obtained from existing high-impedance RF coil, e.g., "self-decoupled RF coil". To further investigate its performance, an 8-channel head coil array using the proposed hairpin resonators loaded with a cylindrical phantom is designed, demonstrating a 19 % increase of the B1+ field intensity compared to the "self-decoupled" coils at 7T. Furthermore, the characteristics of the hairpin RF coils are evaluated using a more realistic human head voxel model numerically. The proposed hairpin RF coil provides excellent decoupling performance and superior RF magnetic field efficiency compared to the self-decoupled high impedance coils. Bench test of a pair of fabricated hairpin coils prove to be in good accordance with numerical results.
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