磁共振成像中涡流效应的仿真

为研究涡流对磁共振(MRI)图像的影响,提出了MRI中涡流效应的仿真方法。在基于Bloch方程的仿真方法的基础上增加描述涡流的数学模型从而实现MRI中涡流效应的仿真。为验证仿真结果,首先在一台0.3T永磁MRI系统上测量了涡流模型的参数,然后在该系统上设计并实现了带有附加梯度的自旋回波(SE)序列用以显示零阶涡流的影响。仿真图像和实际图像均显示了和理论分析相符的混叠伪影,同时利用仿真程序补偿实际接收信号,可以明显地减小重建图像的伪影。以上实验结果验证了仿真程序的正确性。

Simulations of eddy current effects in MRI images

A magnetic resonance imaging (MRI) simulator was developed to investigate the effects of eddy currents on MRI images. The simulator is based on the Bloch equation plus a mathematical eddy current model whose parameters were measured on a 0.3T permanent magnet MRI system. A modified spin-echo (SE) sequence with an additional gradient pulse was implemented to display the zero-order eddy currents caused ghosts on the SE images on this MRI system. Both the real and simulation images display Nyquist ghosts which are predicted from MRI principles. The Nyquist ghosts in real image are significantly suppressed by proper phase compensation predicted by the simulator.