超短激光脉冲作用下生物组织体光学响应的时域和频域分析──Dirichlet边界条件和无向点激励源

A TEMPORAL AND FREQUENCY DOMAIN ANALYSIS OF THE OPTICAL RESPONSES IN TISSUE ACTED BY ULTRA-SHORT LASER PULSE──DIRICHLET BOUNDARY CONDITION AND ISOTROPIC POINT SOURCE

生物组织体在超短激光脉冲激励下的表面光学响应特性，如光子平均飞行路径、光通量、相移和调制深度等，在光学时域及频域无损测量、组织体光谱学和光学三维成象研究中具有重要的意义，而生物组织体对近红外和可见光呈现的高散射特性使得激励光子在组织体内的传输行为复杂化，精确地测定和计算上述光学响应量一直是人们感兴趣的问题．本文基于描述组织体内光子传输的扩散方程模型，阐述了时域、频域测量的等效性，从无限空间几何结构出发，逐次导出了常见几何形状均匀组织体光学响应的解析表示，在此基础上给出了典型参数下的计算结果并讨论了计算中可能出现的问题及其解决方法．

The optical responses within a tissue stimulated by ultra--short laser pulse,such as meantime of photon flight, photon flux, phase shift and modulation depth, have been playing significant roles in the studies of tissue optical specroscopy and tomographic imaging. Unfortunately,the behavior of photon propagation in such a turbid medium is much complicated by highly scattering characterization of the tissue,and many attempts have been made for the accurate measurements and computations of the responses aforementioned. Starting from infinite medium case,the concisely analytic solutions for the optical responses in homogeneous tissues with clinically -- concerned geometries are accessed successively,and the equivalency between time--and frequency--domain measurements is stated in this article, based on the photon diffusion theory. Numerical computations are performed for the tissues of typical opticl parameters from the derivations,for which the outlets to some computational difficultiesare proposed.