Liang Xiao, Tang Xin, Tang Weinan, Gao Jia-Hong
Department of Information Engineering, College of Information Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China.
Center for MRI Research, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China.
Rev Sci Instrum. 2014 Sep;85(9):094705. doi: 10.1063/1.4894657.
A home-made high-field magnetic resonance imaging (MRI) spectrometer with multiple receiving channels is described. The radio frequency (RF) transceiver of the spectrometer consists of digital intermediate frequency (IF) circuits and corresponding mixing circuits. A direct digital synthesis device is employed to generate the IF pulse; the IF signal from a down-conversion circuit is sampled and followed by digital quadrature detection. Both the IF generation and the IF sampling use a 50 MHz clock. An oven-controlled crystal oscillator, which has outstanding spectral purity and a compact circuit, is used as the local oscillator of the RF transceiver. A digital signal processor works as the pulse programmer of the spectrometer, as a result, 32 control lines can be generated simultaneously while an event is triggered. Field programmable gate array devices are utilized as the auxiliary controllers of the IF generation, IF receiving, and gradient control. High performance, including 1 μs time resolution of the soft pulse, 1 MHz receiving bandwidth, and 1 μs time resolution of the gradient waveform, is achieved. High-quality images on a 1.5 T MRI system using the spectrometer are obtained.
本文描述了一种自制的具有多个接收通道的高场磁共振成像（MRI）光谱仪。该光谱仪的射频（RF）收发器由数字中频（IF）电路和相应的混频电路组成。采用直接数字合成装置产生中频脉冲；对来自下变频电路的中频信号进行采样，随后进行数字正交检测。中频生成和中频采样均使用50 MHz时钟。一种具有出色频谱纯度且电路紧凑的恒温控制晶体振荡器被用作射频收发器的本地振荡器。数字信号处理器作为光谱仪的脉冲编程器，因此在触发事件时可同时生成32条控制线。现场可编程门阵列器件被用作中频生成、中频接收和梯度控制的辅助控制器。实现了高性能，包括软脉冲1 μs的时间分辨率、1 MHz的接收带宽以及梯度波形1 μs的时间分辨率。使用该光谱仪在1.5 T MRI系统上获得了高质量图像。
