高场磁共振中基于梯度编码的自动匀场方法的研究

均匀的静磁场是核磁共振（NMR）获得高分辨谱图、精细结构信息的基础，随着磁场强度不断提高，匀场难度不断加大，如何有效地提高磁场均匀性是高场NMR一个重要研究课题。基于梯度编码的自动匀场方法是目前最为有效的匀场方法，但其也存在梯度编码易受到磁场不均匀性干扰、三维梯度匀场耗时较长及需要特殊硬件支持等不足。本项目拟开展如下研究：（1）基于Bloch方程建立不均匀磁场中利用梯度编码测量磁场分布的理论模型，发展一种迭代逼近的重建算法，消除磁场不均匀性对梯度编码的干扰，提高梯度匀场准确性。（2）在三维梯度匀场中，利用随机采样的相位编码方式，实现更高效率的信号采集，提高4～8倍匀场效率。（3）设计可由脉冲序列实时控制的室温匀场电源，扩展梯度匀场适用范围。（4）将新硬件和方法模块化，集成于自主研发的高场NMR波谱仪。本项目的实施，将有助于提高高场NMR自动匀场方法实用性，为高场NMR普及提供有力技术支撑。

Uniform static magnetic field is a necessary condtion to obtain the high-resolution spectra and fine chemical structure information. Shimming becomes more difficult and time-consuming since the requirement of the uniformity of magnetic field is increased in high-field NMR. Although compared with conventional manual or computerised search methods, gradient shimming initiated a new era in terms of operation and efficiency, there remain aspects that inhibit fully automated shimming with a result of guaranteed quality in High-field NMR. The major reasons for this limitation are that the restruction algorithm of mapping field distribution based on phase difference is not accurate, and it will take long time in 3D gradient shimming. In this project, we will focus on the following work: (1) Design a new iterative field mapping restruction method based on theoretical investigation to eliminate the interference of field inhomogeneity on gradient encoding and improve the accuracy of gradient shimming. (2) Improve 4~8 times shimming efficiency by introducing random sampling technique in phase encoding dimension of three-dimensional gradient shimming. (3) Expand the scope of the gradient shimming by inventing a new shimming power which can be controlled in real-time by pulse sequence. (4) Develop an automatic shiming module and integrate it to homebuilt high-field NMR spectrometer. The implementation of this project will improve the accuracy and robustness of automatic shimming method, and will be also helpful of improving universality of high-field NMR.