中文摘要：

射频脉冲的频率选择性直接影响磁共振成像的质量，而射频脉冲的优化设计又归结为对Bloch方程的求解．尽管在某些情况下Bloch方程存在解析解，但由于其缺乏通用性而且形式上过于复杂而难于得到实用．本文提出一种Bloch方程的精细时程积分算法，并结合全局优化算法给出一个完整的射频脉冲设计方案．精细积分算法具有高效、高精度的特点，对于射频脉冲的设计很有裨益．数值算例表明，设计所得的射频脉冲具有较好的频率选择性．

英文摘要：

Solving the Bloch equations is a core procedure in the optimal design of radio frequency pulses, which has direct impacts on the quality of acquired images in magnetic resonance imaging. Although the analytical solutions of the Bloch equations exist under some circumstances, they hardly can be applied for practical use because of their complexity and lack of generality. In this paper, we employ precise time integration to solve the Bloch equations. Based on a high precision algorithm and in conjunction with a global optimization algorithm, we provide a complate procedure for the design of radio frequency pulses. The numerical data listed at the end of this paper demonstrate that the pulses derived from our algorithm have good frequency selectivity.