Yan Xinqiang, Cao Zhipeng, Grissom William A
Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.
Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA.
Magn Reson Med. 2016 Jun;75(6):2545-52. doi: 10.1002/mrm.26239. Epub 2016 Apr 15.
To implement and validate a hardware-based array-compressed parallel transmission (acpTx) system.
In array-compressed parallel transmission, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil-to-channel combinations. A two channel-to-eight coil array compression network was developed using power splitters, attenuators and phase shifters, and a simulation was performed to investigate the effects of coil coupling on power dissipation in a simplified network. An eight coil transmit array was constructed using induced current elimination decoupling, and the coil and network were validated in benchtop measurements, B1+ mapping scans, and an accelerated spiral excitation experiment.
The developed attenuators came within 0.08 dB of the desired attenuations, and reflection coefficients were -22 dB or better. The simulation demonstrated that up to 3× more power was dissipated in the network when coils were poorly isolated (-9.6 dB), versus well-isolated (-31 dB). Compared to split circularly-polarized coil combinations, the additional degrees of freedom provided by the array compression network led to 54% lower squared excitation error in the spiral experiment.
Array-compressed parallel transmission was successfully implemented in a hardware system. Further work is needed to develop remote network tuning and to minimize network power dissipation. Magn Reson Med 75:2545-2552, 2016. © 2016 Wiley Periodicals, Inc.
实现并验证一种基于硬件的阵列压缩并行传输（acpTx）系统。
在阵列压缩并行传输中，少量发射通道驱动大量发射线圈，这些线圈通过一个实现优化线圈到通道组合的阵列压缩网络相连。利用功率分配器、衰减器和移相器开发了一个两通道到八线圈的阵列压缩网络，并进行了模拟以研究在简化网络中线圈耦合对功率耗散的影响。使用感应电流消除去耦构建了一个八线圈发射阵列，并在台式测量、B1 + 映射扫描和加速螺旋激发实验中对线圈和网络进行了验证。
所开发的衰减器的衰减与预期衰减相差在0.08 dB以内，反射系数为 -22 dB或更好。模拟表明，与隔离良好（-31 dB）的情况相比，当线圈隔离不良（-9.6 dB）时，网络中的功率耗散高达3倍。与分开的圆极化线圈组合相比，阵列压缩网络提供的额外自由度在螺旋实验中使平方激发误差降低了54%。
阵列压缩并行传输已在硬件系统中成功实现。需要进一步开展工作来开发远程网络调谐并最小化网络功率耗散。《磁共振医学》75:2545 - 2552，2016年。© 2016威利期刊公司。
