Vaughan J T, Hetherington H P, Otu J O, Pan J W, Pohost G M
Department of Medicine, University of Alabama at Birmingham 35294.
Magn Reson Med. 1994 Aug;32(2):206-18. doi: 10.1002/mrm.1910320209.
A tuned transmission line resonator has been developed in theory and in practical design for the clinical NMR volume coil application at 4.1 tesla. The distributed circuit transmission line resonator was designed for high frequency, large conductive volume applications where conventional lumped element coil designs perform less efficiently. The resonator design has made use of a resonant coaxial cavity, which could be variably tuned to the Larmor frequency of interest by tunable transmission line elements. Large head- and body-sized volumes, high efficiencies, and broad tuning ranges have been shown to be characteristic of the transmission line resonator to frequencies of 500 MHz. The B1 homogeneity of the resonator has been demonstrated to be a function of the electromagnetic properties of the load itself. By numerically solving Maxwell's equations for the fully time-dependent B1 field, coil homogeneity was predicted with finite-element models of anatomic structure, and inhomogeneities corrected for. A how-to exposition of coil design and construction has been included. Simple methods of quadrature driving and double tuning the transmission line resonator have also been presented. Human head images obtained with a tuned transmission line resonator at 175 MHz have clearly demonstrated uncompromised high field advantages of signal-to-noise and spatial resolution.
理论上和实际设计中均已开发出一种调谐传输线谐振器，用于4.1特斯拉的临床核磁共振体线圈应用。分布式电路传输线谐振器是为高频、大导电体积应用而设计的，在这些应用中，传统的集总元件线圈设计效率较低。该谐振器设计采用了谐振同轴腔，可通过可调传输线元件将其可变调谐到感兴趣的拉莫尔频率。已证明传输线谐振器具有大尺寸头部和身体体积、高效率以及高达500 MHz频率的宽调谐范围等特性。已证明谐振器的B1均匀性是负载本身电磁特性的函数。通过对完全随时间变化的B1场数值求解麦克斯韦方程组，利用解剖结构的有限元模型预测了线圈均匀性，并对不均匀性进行了校正。文中还包含了线圈设计与构造的操作说明。此外，还介绍了传输线谐振器的正交驱动和双调谐的简单方法。在175 MHz下使用调谐传输线谐振器获得的人体头部图像清楚地展示了在信噪比和空间分辨率方面不受影响的高场优势。
