【作者】 张连顺；

【导师】 张春平；

【作者基本信息】 南开大学 ， 凝聚态物理， 2003， 博士

【摘要】 生物组织中的光传输是组织光学的研究热点之一,因为决定组织内光传输的光学特性参数与组织的生理和病理状态有关,了解光在组织中的空间和时间分布,对光动力学治疗、医学成像、监测组织的生理状态和组织结构等的研究都有重要的理论和实际意义,因此本论文对光与生物组织的相互作用及生物组织光学特性参数的测量进行了研究。从光的传输理论出发,在漫射近似下获得了生物组织内光传输的漫射近似方程,并就无限细光束在不同的边界条件下、平面平行光垂直入射到半无限厚组织以及无限细光束垂直入射到两层结构的半无限厚组织的漫射方程进行了求解,首次从理论上获得了组织表面漫射光分布的解析表达式。为验证漫射理论的准确性,用Monte Carlo方法模拟了组织内的光分布,通过将Monte Carlo模拟结果与漫射近似理论比较以及曲线拟合,得出在无限细光束垂直入射到半无限厚介质的情况下,应用外延边界条件并且定义漫射系数D与吸收系数无关时,所得的漫射解较其他情况下更精确,并且通过曲线拟合的方法,首次确定了漫射近似解的适用范围; 通过Monte Carlo模拟证明了由傅立叶变换得到的两层组织模型的漫射方程解的正确性。设计和建立了一套无损测量生物组织光学特性参数的实验装置,通过对生物组织模拟液Intralipid-10%的测量和校验,证明测量装置测量吸收系数和有效散射系数的误差分别为:△μ_a/μ_a=2.8%、△μ_s′/μs′=5.2%; 利用该装置对实际生物组织牛肌肉、猪肌肉、鸡大胸进行了测量,获得了相应的吸收系数和有效散射系数。建立了光纤耦合器的光学相干层析系统,该系统具有20μm的横向分辨率和26μm轴向分辨率,并可在3分钟内获得1幅100×100像素(2mm×2mm)的层析图; 通过分析施加在压电陶瓷上的信号幅度和频率对测量信号的影响,得出施加在压电陶瓷上的电压并不是越大越好,而是随施加电压的增大作类似周期性的变化,并且施加电压在7.5V附近时效果最好; 为了减少压电陶瓷的热效应对绕在压电陶瓷上的光纤的影响,探测频率应选在远离压电陶瓷谐振频率较好,经过测量发现所使用的压电陶瓷的谐振频率为20kHz ,探测频率选在6kHz附近比较合适; 基于所建立的OCT测量装置,用焦点追迹更多还原

【Abstract】 In the past few years there has been much interest in photon migration in tissue. As the optical scattering and absorption coefficients of biological tissue are related to the tissue morphology and biochemistry, and an understanding of the propagation of light in biological tissue is essential for the use of light for medical diagnosis and therapy, so the light transport in tissue and measurement of optical properties of biological tissues were studied all-round in this dissertation. Based on the light transport theory, the diffusion equation for light transport in tissue was obtained. The diffusion equation was solved with different boundary conditions for semi-infinite geometry, when a narrow collimated light was normally incident upon the surface of a tissue. The case of plane-wave collimated onto the tissue surface was also considered. Light propagation in two-layered turbid media having an infinitely thick second layer was investigated in the steady state and frequency domains. To test the accuracy of the diffusion theory, we simulated the distribution of light in the tissue by Monte Carlo method. Analytical expressions from diffusion theory are compared with Monte Carlo simulations. The effects of the choice of the boundary conditions and diffusion coefficients on the accuracy of the optical parameters are quantified, and criteria for accurate curve-fitting algorithms are developed. It is shown that the error in deriving the optical coefficients is considerably smaller for the solution, which uses the extrapolated boundary condition (EBC) and the diffusion coefficient independent of absorption coefficient than the other three solutions. Monte Carlo simulation also confirmed the results obtained from the diffusion equation for two-layered turbid media. A new experimental method has been developed to determine the scattering and absorption characteristics of a turbid material non-invasively, From the measurement of Intralipid-10%, it is demonstrated that the accuracy of the absorption and reduced scattering coefficients determined by our set were ?μ a μa=2.8%、 ?μ s′ μs′=5.2% respectively. The tissues of ox, pig, and chicken were measured by the experimental set and the absorbing and reduced scattering coefficients were acquired respectively. An optical coherent tomography system was established. The system has the resolution of 20 μ mtransversely and 26 μ min axis direction. An OCT image of 100×100 pixels(2mm×2mm)can be captured within 3 minutes. We studied the relation between the detected signal and the voltage or frequency, which was inputted to the piezoelectric ceramic. The results showed that the detected signal changed resembling periodical with the voltage and the detected signal was maximum when the voltage was 7.5V. To reduce the heat effect of piezoelectric ceramic to the optic fiber, we selected the frequency far away from the resonance frequency of the piezoelectric ceramic. The measured resonance frequency was 20kHz , so we selected 6kHz as the input frequency of piezoelectric ceramic. Two kinds of methods for measuring the thickness and refractive index of bio-tissue simultaneously are presented, i.e, the “the focus tracking method” and the “optical path shifting method”. The refractive index of subsurface of a fresh cucumber was measured by using 1300nm and 850nm light source. The results were 1.351±0.005 and 1.364±0.005 for 1300nm and 850nm respectively. From theoretical analysis, we showed that optical properties of tissue can be determined from backscattered power curves measured by a OCT. Our approach was based on a first-order scattering theory that relates the backscattered power to the total and backscattering coefficients of a tissue.更多还原