Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Magn Reson Med. 2013 Jul;70(1):276-89. doi: 10.1002/mrm.24462. Epub 2012 Aug 13.
A complete high-efficiency transmit amplifier unit designed to be implemented in on-coil transmit arrays is presented. High power capability, low power dissipation, scalability, and cost minimization were some of the requirements imposed to the design. The system is composed of a current mode class-D amplifier output stage and a voltage mode class-D preamplification stage. The amplitude information of the radio frequency pulse was added through a customized step-down DC-DC converter with current amplitude feedback that connects to the current mode class-D stage. Benchtop measurements and imaging experiments were carried out to analyze system performance. Direct control of B1 was possible and its load sensitivity was reduced to less than 10% variation from unloaded to full loaded condition. When using the amplifiers in an array configuration, isolation above 20 dB was achieved between neighboring coils by the amplifier decoupling method. High output current operation of the transmitter was proved on the benchtop through output power measurements and in a 1.5T scanner through flip angle quantification. Finally, single and multiple channel excitations with the new hardware were demonstrated by receiving signal with the body coil of the scanner.
本文提出了一种完整的高效率发射放大器单元，旨在应用于线圈内发射阵列。设计要求包括高功率能力、低功耗、可扩展性和成本最小化。该系统由电流模式 Class-D 放大器输出级和电压模式 Class-D 前置放大器级组成。通过定制的降压直流-直流转换器添加射频脉冲的幅度信息，该转换器具有电流幅度反馈，连接到电流模式 Class-D 级。进行了台式测量和成像实验来分析系统性能。可以直接控制 B1，其负载灵敏度从空载到满载条件下的变化小于 10%。当在阵列配置中使用放大器时，通过放大器去耦方法实现了相邻线圈之间超过 20dB 的隔离。通过输出功率测量和在 1.5T 扫描仪中通过翻转角量化，在台式机上证明了发射器的高输出电流操作。最后，通过使用扫描仪的体线圈接收信号，演示了新硬件的单通道和多通道激励。
