Institute of Neuroscience and Medicine -4, Forschungszentrum Jülich, Jülich, Germany.
Institute of Neuroscience and Medicine -11, Forschungszentrum Jülich, Jülich, Germany.
PLoS One. 2020 Aug 17;15(8):e0237494. doi: 10.1371/journal.pone.0237494. eCollection 2020.
Modern magnetic resonance imaging systems are equipped with a large number of receive connectors in order to optimally support a large field-of-view and/or high acceleration in parallel imaging using high-channel count, phased array coils. Given that the MR system is equipped with a limited number of digitizing receivers and in order to support operation of multinuclear coil arrays, these connectors need to be flexibly routed to the receiver outside the RF shielded examination room. However, for a number of practical, economic and safety reasons, it is better to only route a subset of the connectors. This is usually accomplished with the use of switch matrices. These exist in a variety of topologies and differ in routing flexibility and technological implementation. A highly flexible implementation is a crossbar topology that allows to any one input to be routed to any one output and can use single PIN diodes as active elements. However, in this configuration, long open-ended transmission lines can potentially remain connected to the signal path leading to high transmission losses. Thus, especially for high-field systems compensation mechanisms are required to remove the effects of open-ended transmission line stubs. The selection of a limited number of lumped element reactance values to compensate for the for the effect of transmission line stubs in large-scale switch matrices capable of supporting multi-nuclear operation is non-trivial and is a combinatorial problem of high order. Here, we demonstrate the use of metaheuristic approaches to optimize the circuit design of these matrices that additionally carry out the optimization of distances between the parallel transmission lines. For a matrix with 128 inputs and 64 outputs a realization is proposed that displays a worst-case insertion loss of 3.8 dB.
现代磁共振成像系统配备了大量的接收连接器，以便在使用高通道数、相控阵线圈进行大视场和/或并行成像加速时能够得到最佳支持。鉴于磁共振系统配备了数量有限的数字化接收器，并且为了支持多核线圈阵列的操作，这些连接器需要灵活地连接到射频屏蔽检查室外的接收器。然而，出于许多实际、经济和安全方面的原因，只对一部分连接器进行布线更好。这通常是通过使用开关矩阵来实现的。这些矩阵具有多种拓扑结构，在布线灵活性和技术实现方面有所不同。一种高度灵活的实现是交叉开关拓扑结构，它允许将任何一个输入路由到任何一个输出，并且可以使用单 PIN 二极管作为有源元件。然而，在这种配置中，长的开放式传输线可能会保持连接到信号路径，导致高传输损耗。因此，特别是对于高场系统，需要补偿机制来消除开放式传输线短截线的影响。选择有限数量的集总元件电抗值来补偿大规模开关矩阵中传输线短截线的影响，这些矩阵能够支持多核操作，这并不是一件简单的事情，而是一个高阶的组合问题。在这里，我们展示了使用启发式方法来优化这些矩阵的电路设计，这些矩阵还可以优化并行传输线之间的距离。对于一个具有 128 个输入和 64 个输出的矩阵，提出了一种实现方案，该方案显示出最坏情况下的插入损耗为 3.8dB。
