A PIN diode controlled dual-tuned MRI RF coil and phased array for multi nuclear imaging
A PIN diode controlled dual-tuned MRI RF coil and phased array for multi nuclear imaging
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DOI：
10.1088/0031-9155/55/9/011
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发表时间：
2010-05-07
影响因子：
3.5
通讯作者：
Muftuler, L. Tugan
中科院分区：
文献类型：
--
作者：
Ha, Seunghoon;Hamamura, Mark J.;Muftuler, L. Tugan
氢原子核以外的核的MR成像已被用于研究人类和动物的代谢。然而，除了氢之外的MRI可观察到的核不那么丰富，因此图像SNR较低。为这些研究开发了双调谐射频（RF）线圈，其中使用氢获得高分辨率结构图像，并通过激发其他核获得代谢信息。使用双调谐线圈，实验者避免了将患者移出和更换RF线圈以成像不同核的不便。这也消除了图像配准问题。然而，使用陷波电路进行双调谐操作的常见方案导致线圈损耗增加以及在两个频率处获得最佳调谐和匹配的问题。在这里，提出了一种新的方法，使用PIN二极管在两个谐振频率之间切换线圈。这种设计消除了对陷波电路的需要以及来自陷波电路电感器的自电阻的相关损耗。在我们使用的工作频率下，电感的等效串联电阻高于PIN二极管的等效串联电阻。为了测试这种新方法的有效性，我们首先构建了两个相同几何形状的表面线圈，一个具有传统的陷阱电路，另一个具有PIN二极管开关。我们还研究了两个线圈的性能时，线圈被分成更短的导体段，通过添加更多的调谐元件。已知将线圈分成较短的导体段有助于减少辐射和电场损耗。我们在两种工作频率下探索了两种线圈的这种效应。最后，设计并制作了一个双调谐接收相控阵天线，并利用PIN二极管电路实现了两个谐振频率之间的切换。传统的双调谐鸟笼线圈的设计和建造传输RF功率。该线圈的一个独特功能是通过两组单独的四个端口馈送RF功率，以实现更均匀的1H和23Na激发。我们证明了，性能显着改善，在两个频率与PIN二极管开关双频操作相比，一个相同的线圈与陷阱电路。
MR imaging of nuclei other than hydrogen has been used to investigate metabolism in humans and animals. However, MRI observable nuclei other than hydrogen are not as abundant and as a result the image SNR is lower. Dual-tuned radio frequency (RF) coils are developed for these studies in which high-resolution structural images are acquired using hydrogen and metabolic information is acquired by exciting the other nucleus. Using a dual-tuned coil, the experimenter avoids the inconvenience of moving the patient out and replacing the RF coil for imaging different nuclei. This also eliminates image registration problems. However, the common scheme of using trap circuits for dual-tuned operation results in increased coil losses as well as problems in obtaining optimal tuning and matching at both frequencies. Here, a new approach is presented using PIN diodes to switch the coil between two resonance frequencies. This design eliminates the need for the trap circuit and associated losses from the self-resistance of the trap circuit inductors. At the operating frequencies we used, the equivalent series resistance of an inductor is higher than that of the PIN diodes. In order to test the efficacy of this new approach, we first built two surface coils of identical geometry, one with the conventional trap circuits and one with the PIN diode switches. We also studied the performances of both coils when the coils are divided into shorter conductors segments by adding more tuning elements. It is known that dividing the coil into shorter conductor segments helps reduce radiation and electric field losses. We explored this effect for both coils at both operating frequencies. Finally, a dual-tuned receive-only phased array was designed and built with the PIN diode circuit to switch between two resonance frequencies. A conventional dual-tuned birdcage coil was designed and built to transmit RF power. A unique feature of this coil is that the RF power is fed through two separate sets of four ports for more uniform 1H and 23Na excitation. We demonstrated that the performance is significantly improved at both frequencies with the PIN diode switched dual-frequency operation compared to an identical coil with a trap circuit.