介绍了高场磁共振成像（MRI）多源发射技术的原理，提出了一种用于高场MRI系统的多源射频信号发射机.它能并行输出多路频率、相位、幅度，可快速独立调节的射频脉冲信号.该射频发射机的实现基于单片现场可编程门阵列（FPGA）和多通道数模转换器（DAC）芯片，FPGA读取预存于双端口随机存取存储器（RAM）中的射频信号参数，并利用读取的参数分别实现每路信号的直接数字频率合成（DDS）和信号调制等核心功能，获得多路数字射频信号；FPGA输出的数字信号经过高性能DAC转化为模拟信号，即所需要的射频信号.该射频发射机在设计中大量采用软件无线电技术，即利用Xilinx提供的IP核实现DDS和信号调制等主要功能，具有集成度高、体积小、灵活度高的优点，同时，该设计可以大大缩短开发时间，有效降低实现的难度和成本，为高场MRI谱仪的多源射频发射机的设计研制提供了一种低成本、高效、高性价比的方案.
A multi-channel parallel radiofrequency (RF) transmitter was developed for high-field magnetic resonance imaging (MRI) scanners. With a single field programmable gate array (FPGA) and a multi-channel digital analog converter (DAC), the transmitter can generate multi-channel RF pulses in parallel. The frequency, phase and amplitude of the RF pulses can be adjusted quickly and independently. The FPGA reads the parameters of the RF pulses previously stored in a dual-port random access memory (RAM), and uses them to carry out modulation and direct digital frequency synthesis (DDS) for each RF pulses, resulting in multi-channel digital RF signals. The digital signals were then converted into analog RF signals with a high-performance DAC. The use of intellectual property core provided by Xilinx greatly reduced development time, difficulty and cost in achieving the main functions of the transmitter, such as DDS and modulation. The developed multi-channel RF transmitter has the merits of high integration, small size, low cost and good universality, providing an efficient component for high field MRI systems.
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