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在MRI中,序列的选择比较丰富,同时也对医学影像的质量有着重要的意义。描述磁共振的基础理论一般采用Bloch方程。如何利用Bloch方程计算和分析复杂的序列对MRI信号的影响,是理解和改善MRI的理论基础。在旋转坐标系下,通过矩阵形式下Bloch方程的解的形式,对序列结构中不同阶段的磁共振信号按照时间先后进行递推,双极性梯度磁场下的自旋回波(SE)序列对MRI信号的影响和理论公式得到推导和数值分析,从结果上验证了其正确性,也为临床上越来越复杂的成像序列的选择和MRI信号的分析提供了理论基础。
In MRI, the sequence selection is rich, but also has important significance for the quality of medical images. The basic theory describing magnetic resonance generally uses the Bloch equation. How to use the Bloch equation to calculate and analyze the influence of complex sequences on MRI signals is the theoretical basis for understanding and improving MRI. Under the rotating coordinate system, the magnetic resonance signals of different stages in the sequence structure are recursively according to time by the form of the solution of the Bloch equation under the matrix form. The spin echo (SE) sequence under the bipolar gradient magnetic field is applied to MRI The effects of the signal and the theoretical formula are deduced and analyzed numerically, and the correctness of the results is verified. It also provides a theoretical basis for the selection of more and more complex imaging sequences and the analysis of MRI signals.