Dardzinski B J, Li S, Collins C M, Williams G D, Smith M B
Center for NMR Research, Pennsylvania State University College of Medicine, Hershey, Milton S. Hershey Medical Center, Hershey, Pennsylvania, 17033.
J Magn Reson. 1998 Mar;131(1):32-8. doi: 10.1006/jmre.1997.1334.
The design and performance of an inductively fed low-pass birdcage radiofrequency (RF) coil for applications at 9.4 T are described where tuning is accomplished by mechanically moving a concentric RF shield about the longitudinal axis of an RF coil. Moving the shield about the RF coil effectively changes the mutual inductance of the system, providing a mechanism for adjusting the resonant frequency. RF shield tuning eliminates adjustable capacitors on the legs of the RF coil, eliminates current imbalances and field distortions, and results in improved B1 field homogeneity and high quality (Q) factors. RF shield tuning and inductive matching provide an isolated resonance structure which is both physically and electrically unattached. Experimental analysis of shield position on both B1 field homogeneity and resonant frequency is provided. Computer simulations of B1 field homogeneity as a function of shield position and shield diameter are also presented. Magnetic resonance microimaging substantiates the usefulness of this design.
本文描述了一种用于9.4T应用的电感馈电低通鸟笼式射频（RF）线圈的设计和性能，其调谐是通过围绕RF线圈的纵轴机械移动同心RF屏蔽来实现的。围绕RF线圈移动屏蔽有效地改变了系统的互感，提供了一种调节谐振频率的机制。RF屏蔽调谐消除了RF线圈支路上的可调电容器，消除了电流不平衡和场畸变，并提高了B1场均匀性和品质因数（Q）。RF屏蔽调谐和电感匹配提供了一种物理和电气上均无连接的隔离谐振结构。提供了关于屏蔽位置对B1场均匀性和谐振频率影响的实验分析。还给出了作为屏蔽位置和屏蔽直径函数的B1场均匀性的计算机模拟。磁共振显微成像证实了该设计的实用性。
