基于非线性梯度编码的磁共振快速成像方法研究

磁共振成像扫描时间长一直是限制其在临床应用的瓶颈问题，其中梯度磁场编码是实现快速成像的关键角色之一。目前依靠线性梯度磁场编码已经基本达到了成像速度的“极限”，而研究非线性梯度磁场编码已经成为进一步提高成像速度的最新趋势之一。先期研究已经表明，通过引入非线性梯度磁场，虽然可以缩减扫描时间，但是其成像机制不仅变得更加非线性和复杂，而且图像中伪影也大增。本项目拟通过优化的波浪梯度来改进非线性梯度磁场下的成像机制，以有效减少快速成像时的伪影，从而实现活体下的高质量快速成像。具体包括：1）研究非线性梯度磁场编码的模型和机制；2）提出优化的非线性梯度磁场编码的欠采样成像轨迹和序列；3）设计和开发高度欠采样下适合非线性梯度编码的图像重建算法；4）实验评估在高度欠采样下非线性梯度成像方法的有效性。本项目的实施将为非线性梯度快速成像的发展提供系统而且有效的理论和方法，从而推动其在临床上的有效应用化。

It is a bottleneck that the scanning time of Magnetic Resonance Imaging (MRI) is long in clinical application, and gradient magnetic field coding is one of the key roles in fast imaging. Currently, conventional linear gradient magnetic field coding has achieved the imaging speed of "limit", and researching nonlinear gradient magnetic field coding has become one of the latest trends to further improve the imaging speed. The preliminary research has shown that nonlinear gradient magnetic field can reduce the scanning time, but the imaging mechanism not only becomes more nonlinear and complex, but also images create more image artifacts. This project is proposed to improve image quality under the nonlinear gradient magnetic fields by optimizing the wave gradient, so as to effectively reduce image artifacts in fast imaging, and realize in vivo fast imaging. The project includes: 1) to study the model and mechanism of nonlinear gradient magnetic field coding; 2) to proposed the optimized trajectory in k-space and pulse sequence of nonlinear gradient magnetic field coding; 3) to develop the image reconstruction algorithm which is suitable for nonlinear gradient coding in the highly under-sampling; 4) to experimentally evaluate the effectiveness of the proposed nonlinear gradient imaging method. The implementation of this project will provide a systematic and effective theory and method for the development of nonlinear gradient fast imaging, and promote its effective application in clinical applications.