一种用于高场MRI的多源射频发射机

A Multi-Channel Radiofrequency Transmitter for High-Field MRI

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 resonanceimaging(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 RFpulses can be adjusted quickly and independently.The FPGA reads the parameters of the RF pulses previously stored in adual-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 analogRF signals with a high-performance DAC.The use of intellectual property core provided by Xilinx greatly reduceddevelopment time,difficulty and cost in achieving the main functions of the transmitter,such as DDS and modulation.Thedeveloped 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.