Fundamental Studies of Photon Migration in Biological Tissues and Their Application to Optical Tomography

This paper reviews the studies of photon migration in biological tissues and its application to optical tomography which were conducted in the Mechanical Engineering Laboratory of Japan’s Ministry of International Trade and Industry. The research subjects range from theoretical and experimental studies of photon migration in random media to the development of image reconstruction algorithms and experiments for optical tomography. The most fundamental theoretical study of the photon diffusion equation has proved that the photon diffusion coefficient is independent of the absorption coefficient while the conventional one is dependent on the absorption coefficient. Experimental studies included the time-resolved spectroscopy and the fabrication of realistic human head phantoms which have five tissue types with different optical properties. Several types of reconstruction algorithms have been developed and verified experimentally. These investigations are pioneering work in the field of biomedical optics in Japan.     

非均匀生物组织中光子迁移的数值方法

导出了一种研究光子在非均匀生物组织中迁移规律的数值方法，并验证该方法的精确性，进一步研究了非均匀生物组织中扩散系数对反射和透射光通量的影响，结果表明扩散系数的非均匀性对光反射和透射的影响不可忽略。     

虚光场对克尔介质中受激原子统计性质的影响

研究了类克尔介质中虚光场效应对受激三能级了的光子统计演化性质的影响。结果表明：虚光场效应导致了受激辐射场的光子统计演化中出现的量子噪声,量子噪声随光场频率的增大而减小,当增大到一定值时,量子噪声几乎消失,原子－场耦合系数的增加使光子统计演化的拉比振荡的振幅加大、频率变快;而介质－场耦合系数的增加使光子统计演化拉比振荡的振幅变小、频率变慢。     

高散射介质中光子扩散成像的线性平移不变性

运用微扰理论探讨了光子扩散成像的线性平移不变性,阐明了光子扩散成像用于生物组织这一高散射介质结构与功能成你的信号形成机理.光子扩散成像所得的图像是介质内部异常结构通过光子扩散成像系统的响应.光子扩散成像系统的作用可用一个脉冲响应函数来表征.     

Topographic Distribution of Photon Measurement Density Functions on the Brain Surface by Hybrid Radiosity-Diffusion Method

An accurate modelling of light propagation in the head is required to develop an algorithm to reconstruct the image of brain activity. Most previous studies have calculated the light propagation in two dimensional models because of their advantage in computation time and memory requirement over three dimensional models. However, in topographic imaging, the sensitivity distribution in the cross sections parallel to the brain surface which cannot be obtained from a two dimensional model is most important to reconstruct the image. In this study, the light propagation in three dimensional adult head models is calculated by finite element method and hybrid radiosity-diffusion method. The light propagation in the adult head is strongly affected by the non-scattering cerebrospinal fluid (CSF) layer surrounding the brain. The sensitive area is shifted toward the deeper region, and is spread around the CSF layer. The intensely sensitive region on the brain surface is broadly distributed between the source and detector. However, the sensitive region does not penetrate into the deeper part of the brain.     

Excess Volume of the Solid/Liquid Interface in Fe-6 at.%Si Bicrystals Wetted by Liquid Zinc

The pressure effect on grain boundary wetting in Fe-6 at.%Si bicrystals of different misorientation angles but constant misorientation axis has been studied. The wetting agent was liquid zinc. It was found that the pressure for the dewetting transition is higher for the near 5 boundary than for the other general boundaries, where is the inverse density of the coincidence sites in the two misoriented crystal lattices. This result was explained assuming a thinner liquid film wetting the near 5 boundary than in the case of nonperiodic grain boundaries. Furthermore, the wetting angle increased with increasing pressure. The wetting angle dependence on pressure could be understood assuming a excess surface volume of the solid/liquid (S/L) interface higher than 0.2 nm. This is considerably higher than the estimated excess volumes of grain boundaries based on computer simulations. To explain this result, it was postulated that in the system studied, where diffusion of Zn, Fe and Si perpendicular to the S/L interface takes place, the S/L interface is relatively thick and the interaction between the two crystals separated by the melt extends over more than 2 nm distance. This long-range interaction was rationalized in terms of clusters of several atoms, detaching from the solid and dissolving in the melt at some distance from the bulk.     

Photon migration of Raman signal in bone as measured with spatially offset Raman spectroscopy

Spatially offset Raman spectroscopy (SORS) is currently being developed as an in vivo tool for bone disease detection, but to date, information about the interrogated volume as influenced by the light propagation and scattering characteristics of the bone matrix is still limited. This paper seeks to develop our general understanding of the sampling depths of SORS in bone specimens as a function of the applied spatial offset. Equine metacarpal bone was selected as a suitable specimen of compact cortical bone large enough to allow several thin slices (600 µm) to be cut from the dorsal surface. Photon migration at 830‐nm excitation was studied with five bone slices and a 380‐µm‐thin polytetrafluoroethylene (PTFE) slice placed consecutively between the layers. To optimize Raman signal recovery of the PTFE with increasing depth within the bone stack required a corresponding increase in spatial offset. For example, to sample effectively at 2.2‐mm depth within the bone required an optimal SORS offset of 7 mm. However, with a 7‐mm offset, the maximum accessible penetration depth from which the PTFE signal could be still recovered was 3.7 mm. These results provide essential basic information for developing SORS technology for medical diagnostics in general and optimizing sampling through bone tissue, permitting a better understanding of the relationship between the offset and depth of bone assessed, in particular. Potential applications include the detection of chemically specific markers for changes in bone matrix chemistry localized within the tissue and not present in healthy bone. © 2015 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd.     

冷原子系综中量子关联光子对的产生

本文在87 Rb冷原子系综中通过自发拉曼散射过程进行了量子关联光子对产生的实验研究,测量了关联光子对的产生率和二阶关联函数g(2)随写光激发率、读光功率以及写光失谐等实验参数的关系曲线。结果表明:随着写光激发率的增加,光子对产生率线性增加,g(2)则不断减小;在小的读光功率处,光子对产生率和g(2)随着读光功率增加而增大,当读光功率超过30 mW后,产生率和g(2)随着读光功率增加反而有所下降;写光频率失谐为-5 MHz时光子对产生率和g(2)均达到最低,增大或减小写光失谐产生率和g(2)均逐渐增加。通过选取合适的实验参数,光子对产生率达到18对/秒,同时g(2)为106。本文的研究结果为产生高质量的纠缠源提供了实验基础。     

ee0A GeV S+Au反应中光子产生的低横动量增强

用建立在LUND弦模型特别是PYTHIA事件产生器基础上的描写极端相对论性核一核碰撞的强子和弦级联模型—JPCIAE研究了入射能量为200A GeV的S+ Au中心碰撞中光子产生.模型同时考虑了部分子QCD散射过程、强子末态相互作用以及强子衰变等光子产生反应道并作了协调处理.JPCIAE模型计算结果很好再现了WA93实验数据所呈现的低横动量增强效应.     

克尔介质中纠缠光与三能级原子作用的光子统计

采用求解薛定谔方程和数值计算方法,研究了克尔介质中双模纠缠相干光场与三能级原子相互作用系统的光子统计性质,分析了双模纠缠相干光场的纠缠程度、克尔介质与光场的耦合强度、双模光的平均光子数和原子基态概率幅对光子统计性质的影响。结果表明：双模纠缠相干光场的纠缠程度对光子统计性质没有明显的影响;克尔效应增强使光子统计性质的时闻演化曲线的振荡频率变大、振荡幅度变小;当保持场模1的平均光子数不变而场模2的平均光子数变小时,光子统计性质的时间演化曲线的振荡幅度变大。     

Airy光束在Kerr介质中的传输特性

通过对非线性薛定谔方程的研究,得出Airy光束在Kerr介质中的崩塌功率及有效束宽演化的解析表达式。经过数值计算发现,Airy光束在聚焦的Kerr介质中,其主瓣在开始传播时始终是会聚的;当输入功率小于临界崩塌功率时,Airy光束主瓣的中心部分出现局部崩塌。在不同的Kerr介质中, Airy光束的形状和传输轨道均能保持不变,如同在自由空间中传播,但光场大小的分布,随着不同的Kerr介质会发生改变:在Kerr的聚焦介质中,光场向中心聚焦;而在散焦的Kerr介质中,光场会发散。     

Coupling of Dirichlet-to-Neumann boundary condition and finite difference methods in curvilinear coordinates for multiple scattering

The applicability of the Dirichlet-to-Neumann technique coupled with finite difference methods is enhanced by extending it to multiple scattering from obstacles of arbitrary shape. The original boundary value problem (BVP) for the multiple scattering problem is reformulated as an interface BVP. A heterogenous medium with variable physical properties in the vicinity of the obstacles is considered. A rigorous proof of the equivalence between these two problems for smooth interfaces in two and three dimensions for any finite number of obstacles is given. The problem is written in terms of generalized curvilinear coordinates inside the computational region. Then, novel elliptic grids conforming to complex geometrical configurations of several two-dimensional obstacles are constructed and approximations of the scattered field supported by them are obtained. The numerical method developed is validated by comparing the approximate and exact far-field patterns for the scattering from two circular obstacles. In this case, for a second order finite difference scheme, a second order convergence of the numerical solution to the exact solution is easily verified.     

克尔介质中双模纠缠相干光与贝尔态原子相互作用系统的光子统计特性

运用全量子理论并结合数值计算方法,研究了克尔介质腔中处于贝尔态的两个全同二能级纠缠原子与双模纠缠相干光场相互作用系统的光子统计特性。讨论了双原子体系的初态、初始光场的平均光子数、双模纠缠相干光场的纠缠程度以及克尔介质与双模光场的耦合强度对光子统计特性的影响。结果表明:忽略克尔介质的作用时,只有当双原子体系的初态为0β1〉或1β1〉时,在一定的条件下才可出现光子的反聚束效应,而当双原子体系的初态为β00〉、1β0〉时,光场在其演化过程中不出现光子的反聚束效应。而当考虑克尔介质的作用时,四种初态下光场演化过程中均有可能出现光子的反聚束效应。光子的反聚束效应出现的次数、时间和深度极其敏感地依赖于初始光场的平均光子数和克尔介质与双模光场的耦合强度,同时也受到双模纠缠光场的纠缠程度的影响。     

导电平板上任意缝隙填充各向异性介质时TM波散射和传输特性分析

简单介绍了用于分析任意口径问题的通用频域方法——广义网络原理,并利用边界积分法和广义网络原理分析导电平板上任意缝隙填充各向异性介质时TM波的散射及传输特性.由于缝隙填充各向异性介质的情形尚未见公开文献报道,作为验证,将本方法退化计算各向同性介质填充时缝隙的散射和传输特性,并与文献结果进行比较.最后,给出了缝隙填充各向异性介质时的算例.     

格子Boltzmann模型平衡分布边界条件和多棱柱排列渗流流场的数值模拟

介绍了适用于多种流场数值模拟的无滑动格子Boltzmann平衡分布边界条件，这一边界条件是以Bounce-Back方法为基础并满足质量、动量守恒的准则.数值计算结果表明平衡分布边界条件克服了Bounce-Back方法在边界上所产生的滑动速度误差效应.利用平衡分布边界条件数值模拟了由棱柱形充填粒子构成的微尺度渗流流场中的Darcy-Forchheimer方程，通过与Lee 和Yang的数值结果比较，该预测结果是足够可靠的. 关键词： 平衡分布边界条件 渗流介质 Darcy-Forchheimer阻力     

Absorption Coefficient Measurements of Strongly Scattering Media Using Time-Resolved Transmittance of a Short Pulse in Near-Infrared (NIR) Wavelength Range

Absorption coefficient measurements of strongly scattering and weakly absorbing media have been performed using time resolved transmittance of a 100 fs pulse through a 30 mm slab containing latex spheres suspended in water and absorbing ink solutions. The scattering and absorption coefficients were selected so that the optical properties of the media were similar to those of biological tissues. Measured curves of time-resolved transmittance of the pulse through the media were used to estimate the optical properties of the media. The experiment was made at two different wavelengths, 784 nm and 810 nm. Estimated absorption coefficients were in good agreement with those measured in a nonscattering case by a spectrophotometer.Presented at the 7th International Workshop on Multiple Scattering Lidar/Light Experiments (MUSCLE7), July 21-23 1994, Chiba, Japan.     

Lattice Boltzmann Simulation of Convection in a Porous Medium with Temperature Jump and Velocity Slip Boundary Conditions

To investigate the convection in a porous medium, a horizontal quiescent layer of one fluid saturating a porous medium heated from bottom is numerically studied using single lattice-Boltzmann method (LBM) and the generalized Navier-Stokes equation proposed by Nithiarasu et al. [P. Nithiarasu, K.M. Seetharamu, and T Sundararajan, Int. J. Heat Mass Trans. 40 (1997) 3955]. Due to the rarefaction, the boundary conditions are considered as both temperature jump and velocity slip. The computational results are validated against the analytical results, and excellent agreement has been obtained. The results have shown that the Rayleigh number is increased with increasing temperature jump, the stabilization effect of temperature is much more significant than that of velocity slip, and the computation stability of present model is better than that of Darcy and Brinkman models.     

一种简化的分析光纤布拉格光栅的时域有限差分束传输法

提出了一种便于分析光纤布拉格光栅(FBG)、基于强制边界条件的简化TD-FD-BPM模型.采用交替隐式法(ADIM)和综合道格拉斯(GD)法,离散化时域束传输方程,获得比普通差分格式低二阶的误差。提出并采用强制边界条件,简化了光波导分析中边界处理问题.重点讨论和确定了在此条件下激励源位置、脉冲形状和径向分布函数、连续波激励条件等.在修正的正弦脉冲激励情况下,通过离散傅利叶变换,直接得到较为理想的短FBG反射谱.此法可减少数值计算时间,直观反映光脉冲传输.     

平稳状态下匹配介质三层漫射方程的空间分辨漫反射

如果应用漫射方程分析和确定生物表面组织的光学特性,就能够确定生物活体是否发生病变,实现生物活体的无损探测。目前,光在生物体内传播常用的基本模型是半无限厚模型和两层介质模型。而实际上,人体组织为多层介质。根据漫射方程理论,在平稳状态条件下,使用外推边界条件,精确给出了匹配介质中平稳状态下三层体系光的漫射方程格林函数的解。通过此解,可以算出空间分辨漫反射。使用蒙特卡罗方法来验证三层体系的漫射方程,发现我们给出的理论解,不仅可以包括与Kienle的结论一致的两层体系模型的空间分辨漫反射的解,而且三层体系漫射方程的空间分辨漫反射解和蒙特卡罗方法基本一致。