Erickson Matthew G, Kurpad Krishna N, Holmes James H, Fain Sean B
Department of Radiology, University of Wisconsin, Madison, Wisconsin 53792, USA.
Magn Reson Med. 2007 Oct;58(4):800-7. doi: 10.1002/mrm.21394.
MR imaging and spectroscopy requires RF fields of high homogeneity. Quadrature volume coils meeting this requirement include the birdcage coil and the TEM resonator. We describe here a quadrature volume coil designed around a modified coaxial transmission line in which multiple inner conductors are arrayed on a circular perimeter and surrounded by a common shield. Current antinodes are established at appropriate points on the inner conductors by series transmission line stubs, either open circuit or short circuit, which terminate the line. Quadrature phasing is generated by a novel circuit constructed from a pair of high-performance current baluns and a commercial quadrature hybrid. The coil is a "pure" TEM coil as it is simply a resonant transmission line. There is no mode structure to consider. The construction of a prototype quadrature four-element coil is described and preliminary test results from this coil in a 4.7T horizontal bore magnet are reported. A related double nuclear coil design for (3)He and (1)H in which two linear transmission line coils are arrayed on a circular perimeter and simultaneously tuned and matched to their respective frequencies is also described. Preliminary tests from this coil in a 1.5T clinical scanner are reported.
磁共振成像和光谱学需要高均匀性的射频场。满足这一要求的正交容积线圈包括鸟笼线圈和TEM谐振器。我们在此描述一种围绕改进的同轴传输线设计的正交容积线圈，其中多个内导体排列在圆形周边上，并被一个公共屏蔽包围。通过串联传输线短截线（开路或短路）在终止线路的内导体上的适当位置建立电流波腹。正交相位由一对高性能电流平衡-不平衡变换器和一个商用正交混合器构成的新型电路产生。该线圈是一个“纯”TEM线圈，因为它仅仅是一条谐振传输线。无需考虑模式结构。描述了一个正交四元线圈原型的构建，并报告了该线圈在4.7T水平孔径磁体中的初步测试结果。还描述了一种相关的用于³He和¹H的双核线圈设计，其中两个线性传输线线圈排列在圆形周边上，并同时调谐并匹配到它们各自的频率。报告了该线圈在1.5T临床扫描仪中的初步测试结果。
