Image reconstruction tomography with only a method for laminar optical single Monte-Carlo simulation

Laminar optical tomography （LOT） is a new mesoscopic functional optical imaging technique. Currently, the forward problem of LOT image reconstruction is generally solved on the basis of Monte-Carlo （MC） methods. However, considering the nonlinear nature of the image reconstruction in LOT with the increasing number of source positions, methods based on MC take too much computation time. This letter develops a fast image reconstruction algorithm based on perturbation MC （pMC） for reconstructing the absorption or scattering image of a slab medium, which is suitable for LOT or other functional optical tomography system with narrow source-detector separation and dense sampling. To calculate the pMC parameters, i.e., the path length passed by a photon and the collision numbers experienced in each voxel with only one baseline MC simulation, we propose a scheme named as the trajectory translation and target voxel regression （TT＆TVR） based on the reciprocity principle. To further speed up the image reconstruction procedure, the weighted average of the pMC parameters for all survival photons is adopted and the region of interest （ROI） is extracted from the raw data to save as the prior information of the image reconstruction. The method is applied to the absorption reconstruction of the layered inhomogeneous media. Results demonstrate that the reconstructing time is less than 20 s with the X - Y section of the sample subdivided into 50 × 50 voxels, and the target size quantitativeness ratio can be obtained in a satisfying accuracy in the source-detector separations of 0.4 and 1.25 mm, respectively.     

无限介质中近场辐射率的P5近似

针对辐射率的漫射近似、P3近似等正向模型在描述小源探距离及低约化反照率介质下光子传输时存在的局限性,推导了用于小源探距离低反照率无限媒质中各向同性稳态点光源下辐射传输方程在P5近似下的解析解,并将P3近似、P5近似计算的辐射率分别和蒙特卡洛模拟结果进行对比.结果表明:在高约化反照率(0.97)条件下,P5近似和蒙特卡洛模拟结果的最大相对误差为13.17%,而P3为41.57%.在低约化反照率(0.69)条件下,最大相对误差分别为27.78%,286.70%.在其他光学参数下,P5近似与蒙特卡洛模拟的最大相对误差均小于P3.在P5适用的范围内舍弃最大特征根相关项,可以简化解析表达式,提高计算速度,且对P5的计算结果影响甚微.稳态辐射率测量系统仿体验证表明,在高、低约化反照率介质中的小源探距离下,由P5近似计算得到的辐射率和实验测量结果相符.     

用于宫颈癌筛查的光电联合检测系统

为了提高宫颈癌的早期筛查效率以合理分配医疗资源,研制了基于光电联合检测的宫颈癌早期筛查系统.系统顶端放置的光电极手持探头采用电脉冲、红光、绿光及近红外光交替分时刺激宫颈组织,通过光电激励和测量,计算得到组织的光电学特征参数——电压衰减常数和相对反射率,用组织分类算法实现了宫颈癌变的判别.将313例临床检验数据与组织病理检验金标准比对,建立了光电激励下组织响应临床数据库.组织分类结果表明,光电联合检测方法比单独光或电的检测在灵敏度、特异性和总符合率上有较大的提高,与组织病理检验结果的对比表明本文所研发系统总符合率达85.1%,对早期宫颈癌的筛查尤其是落后地区宫颈癌的筛查具有重要意义.