一种高分辨率的磁共振成像梯度信号发生器

A high⁃resolution gradient signal generator for magnetic resonance imaging

PCM1794是一款24位字长、串行输入、双极性电压输出的高精度数模转换芯片,拥有出色的动态性能,信噪比高达129 dB。针对磁共振成像谱仪小型化、高集成度的发展需求,文中提出一种高分辨率的磁共振成像梯度信号发生器,采用PCM1794芯片作为数模转换器,以单片FPGA芯片作为梯度信号计算及控制单元的核心。该梯度信号发生器输出高精度的独立的X、Y、Z三个方向的梯度波形和静磁场梯度波形(用于静磁场B0的涡流补偿)。其预加重计算周期为1μs,波形更新周期最小也可达1μs。通过优化FPGA程序的计算架构节省了硬件乘法器资源的消耗,降低了对FPGA性能的要求,有利于构建高集成度的紧凑型谱仪。通过软件仿真和实际测试结果表明,该梯度信号发生器能够产生高精度梯度波形,满足磁共振成像对于梯度发生的要求。

The PCM1794 is a 24⁃bit,serial input,bipolar voltage output and high⁃precision digital⁃to⁃analog conversion chip with excellent dynamic performance and signal⁃to⁃noise ratio of 129 dB.In response to the development needs of miniaturization and high integration of magnetic resonance imaging spectrometer,a high⁃resolution gradient signal generator for magnetic resonance imaging is proposed in the paper,in which PCM1794 chip is adopted as the digital⁃to⁃analog converter and a single FPGA device as the core of the gradient signal calculation and control unit.The gradient signal generator outputs high⁃precision independent gradient waveforms in X,Y and Z directions and static magnetic field gradient waveforms(for eddy current compensation of static magnetic field B0).Its pre⁃emphasis calculation period is 1μs,and the waveform update period can reach 1μs as small.By optimizing the computational architecture of the FPGA program,the resource consumption of hardware multiplier is saved and the performance requirements of the FPGA are reduced,which is conducive to the construction of a highly integrated compact spectrometer.The results of software simulation and actual testing show that the gradient signal generator can generate high⁃precision gradient waveforms and meet the requirements of magnetic resonance imaging for gradient generation.