采用辐射传输方程的简化三阶球谐函数（SP3）近似作为时域荧光扩散层析成像（FDOT）的正向模型，克服了球谐函数近似法（PN）公式复杂，计算量大的缺点和扩散近似（DA）理论对于低散射组织体的不适用性。考虑到时域模式可以同时重建荧光产率和寿命，且技术上较频域模式更容易实现，因此采用时域模型，应用源自广义脉冲谱技术（GPST）的特征数据类型，将基于DA-GPST推广到SP3方程，发展了一套基于SP3-GPST的FDOT图像重建方法。数值模拟结果表明，SP3-GPST重建结果优于DA-GPST。

The third-order simplified spherical harmonics approximation to radiative transfer equation is utilized as forward model for the fluorescence diffuse optical tomography (FDOT). This algorithm overcomes the drawback of big computation consumption of PN approximation and limitation that DA is unapplicable to the low-scattering tissue. The time-domain technique offers the potential advantages in directly measuring lifetime and has the best performances of simultaneously recovering of fluorescent yield and lifetime distributions, as well as resolving multiple components. On these bases, an image reconstruction method of generalized pulse spectrum technique based on the SP3 equation(SP3-GPST) is presented, and it is an extent of generalized pulse spectrum technique based on the diffusion equation(DA-GPST). Simulation results show that SP3-GPST performs better than DA-GPST.