基于微扰蒙特卡罗的薄层状组织光学参数重构技术

针对层状组织体的光学参数（吸收系数和散射系数）快速重构问题展开讨论.发展了基于漫反射测量的适合于胃、宫颈等内脏薄层状组织光学参数重构的微扰蒙特卡罗模拟.数值模拟结果显示,该方法能够有效地利用漫反射光强重构临床应用范围内的光学参数,对单层模拟体的吸收系数和散射系数的重构误差均不大于±3%,对双层模拟体的重构误差小于10%,且两参数的重构之间几乎没有互扰.使用固体模型对上述算法进行的实验显示,重构出的散射参数与真值的误差小于±10%.进行一组光学参数重构耗时不超过1 min.结果表明,该方法可快速、准确地重构光学参数,为内脏器官近红外早期癌症诊断的临床应用提供保障.     

超声仿人体组织材料声学参量测量研究

为了准确可靠地测量超声仿人体组织材料的声学参数,测量和评价仿组织体模中的填充材料,本文搭建了基本声学参数测量装置,编制了数据采集处理软件,实现了对材料声速、声衰减和超声背向散射系数的自动测量。针对不同成份的样品模块,利用本文所述系统对样品声学参数进行了测量。结果表明,声速和声衰减测量结果与理论值基本一致,背向散射系数随着超声频率的提高有所增大。     

基于印压法的软组织模体的杨氏模量测量

研制了基于印压法的软质材料杨氏模量的测量装置,通过有限元仿真方法确定杨氏模量与印压曲线的关系的系数,从而实现对仿组织弹性样本进行杨氏模量量值的标定;用瞬时弹性成像设备对仿组织弹性模体进行测量,其结果与印压法测量结果的一致性,验证了弹性量值传递的可行性。     

基于时间相关单光子计数的非接触式荧光层析成像系统

基于时间相关单光子计数(TCSPC)技术原理,研究了一套面向早期乳腺癌检测的时域荧光层析成像系统,系统采用非接触式空间光扫描测量方式,相对于传统的光纤接触式测量方法,可增大空间采样量、减小测量误差、提高空间分辨率.通过仿体实验对系统的成像质量进行了验证,结果表明:单目标仿体实验能较好地对荧光产率与寿命进行重建;在双目标仿体荧光产率的重建中,可有效对中心距为20mm、边距为15mm的目标体进行分辨,且对不同浓度荧光剂目标的重建具有较好的线性.实验结果证明系统应用于乳腺检测的可行性,进一步发展可有望应用于临床乳腺成像中.     

微细管道内表面光电检测及三维重构系统

基于位置传感器PSD和光学三角原理,开发了一种适于空间曲线型微细管孔内表面三维重构的检测系统.该系统主要由管道机器人、形貌检测器和曲率检测器等部分组成.形貌检测器可以采集管道内壁截面信息,并计算出截面环上的点在局部坐标系中的位置.曲率检测器负责测量管孔中心轴线在检测器采样位置处的局部几何性质,并完成管道中轴线的重构.在管道机器人的驱动下,根据上述两方面提供的数据以及其前进步距,可以实现管道内表面的三维重建.实验结果表明,利用该技术检测的管道时,管道曲率半径的相对检测精度可以达到±2%,内表面缺陷及内径的测量精度可以达到±0.1mm.     

新型科里奥利粉料流量测控系统

对北京航空航天大学自主研发的基于科里奥利原理的新型固体粉料流量测控系统进行介绍,包括该系统的测量原理及总体设计,测控系统的机械秤体、控制仪表的软硬件设计,测控系统基于现场总线Profibus-DP与以太网的现场总线通信设计,以及该测控系统的应用现状与最新研究成果。结果表明,该系统运行稳定,测量准确,达到了最初的设计要求。     

地面密集度测试系统的研制

利用基于图像识别的自动跟踪技术,研制了自动测试火炮地面密集度的装置.该装置由激光测距仪、可控变焦CCD摄像机、二维自动转台、无线通讯模块等组成,可在复杂的背景图像中自动识别落弹点的位置,并控制转台将激光测距仪对准该位置,测量出该位置的坐标,在4km的范围内精度可达到2 m.GPRS无线通讯装置可将现场的图像及测试结果传输到后方.与人工测量方式相比,该系统具有测量速度快、精度高以及安全性好等特点.     

Haar整数频域变换耦合动态引力模型的加密算法

目的实现数字图像与QR二维码信息的安全保密。方法基于频域-空域双重加密的思想,提出Haar整数频域变换耦合动态引力模型的图像无损加密认证算法,并将该算法应用于QR二维码的加密传输。首先引入Haar小波变换,定义频域系数修整模型,将明文分解为4个子带;随后基于256位外部密钥,迭代3D Chen系统,建立混沌序列择取与优化机制,有效消除瞬态效应,从而输出3个优化子序列,通过融合这些序列,输出一组密钥流,基于升序排列,形成位置扰乱源,对4个子带完成频域置乱,再利用Haar逆变换,形成置乱密文;构建像素点质量动态估计模型,改进引力模型,对置乱密文完成空域扩散;定义密文深度分段扩散机制,对初始密文完成二次扩散,提高密文的NPCR(Number of Pixels Change Rate)与UACI(Unified Average Change Insensitive)值;最后,引入HASH检测机制,赋予算法决策功能,对图像在传输中是否遭到攻击进行认证。结果与基于混沌理论的加密技术相比,文中算法具备更高的安全性与抗剪切攻击能力,且解密图像的失真度最小;同时,对QR二维码信息也具有较高的保密度和较低的解密失真度,在安全加密的同时,也较好地保留了QR二维码的原有结构信息。结论文中算法具有较高的安全性,能够安全保护图像与QR二维码在网络中安全传输,在包装与印刷防伪条码领域具有较好的实际应用价值。     

子结构传感器位置优化和响应重构

提出了一种子结构传感器位置优化和未测点结构响应重构的方法。按照结构体系,将整体结构划分为多个子结构,减少研究对象的自由度数目,然后对每个子结构单独进行传感器位置优化和响应重构。由于每个子结构的自由度数目都远小于整体结构,该方法有利于提高传感器位置优化和响应重构的效率。以最小化重构误差为目标方程,确定子结构传感器的位置和数目,并利用优化位置上的测量信息重构未测点的响应。数值算例和试验分析结果显示,利用有限测点测量信息重构的结构响应,在时域和频域里均能与计算或测量响应吻合良好。该方法不需要分割隔离各子结构和考虑复杂的边界条件,有利于该方法在大型土木工程结构中的使用。     

一种高精度质心测量系统设计与分析

为了解决航空、航天、兵器及其他武器装备中对质心位置的高精度测量问题,实现飞行器质心位置的高精度测量,本文设计了一种基于质量反应法的高精度质心测量系统,介绍了其测量原理,描述了该系统结构组成和测量方法,并对实验数据及其溯源性进行了分析,结果表明系统能达到较高的测量精度,对武器装备的研制、试验和生产起到保障作用,并由此得出了利用该装置建立质心量值溯源体系的可行性。     

Simultaneous reconstruction of absorption and scattering maps with ultrasound localization: feasibility study using transmission geometry

We report the experimental results of the simultaneous reconstruction of absorption and scattering coefficient maps with ultrasound localization. Near-infrared (NIR) data were obtained from frequency domain and dc systems with source and detector fibers configured in transmission geometry. High- or low-contrast targets located close to either the boundary or the center of the turbid medium were reconstructed by using NIR data only and NIR data with ultrasound localization. Results show that the mean reconstructed absorption coefficient and the spatial distribution of the absorption map have been improved significantly with ultrasound localization. The improvements in the mean scattering coefficient and the spatial distribution of the scattering coefficient are moderate. When both the absorption and the scattering coefficients are reconstructed the performance of the frequency-domain systemis much better than that of the dc system.     

Measurement of the absorption and scattering properties of turbid liquid foods using hyperspectral imaging

A hyperspectral imaging system in line scanning mode was used for measuring the absorption and scattering properties of turbid food materials over the visible and near-infrared region of 530-900 nm. An instrumental calibration procedure was developed to compensate for the nonuniform instrument response of the imaging system. A nonlinear curve-fitting algorithm for a steady-state diffusion theory model was proposed to determine absorption (mua) and reduced scattering coefficients (mu's) from the spatially resolved hyperspectral reflectance profiles. The hyperspectral imaging system provided good measurement of mua and mu's for the simulation samples made of Intralipid scattering material and three absorbers (blue dye, green dye, and black ink) with average fitting errors of 16% and 11%, respectively. The optical properties of the fruit and vegetable juices and milks were determined. Values of the absorption and reduced scattering coefficient at 600 nm were highly correlated to the fat content of the milk samples with the correlation coefficient of 0.995 and 0.998, respectively. Compared to time-resolved and frequency-domain techniques, the hyperspectral imaging technique provides a faster and simpler means for measuring the optical properties of turbid food and agricultural products.     

利用残缺样本声速重构声速剖面

用经验正交函数(experiential orthogonal functions,EOF)表示声速剖面受限于样本声速的测量深度,应用该方法重构声速剖面只能计算到样本中最浅剖面的深度。要想进行全海深声速剖面的重构,必须对残缺的样本声速进行合理地外延。为此,首先对样本中温度和盐度进行了外延,然后根据声速经验公式计算得到了全海深的样本声速。在此基础上,通过解多元方程组的办法求解经验正交函数系数达到了声速剖面重构的目的。结果表明,提出的声速剖面外延方法是有效的。另外,只要知道声速剖面变化较剧烈深度上的3个点的声速值就能重构声速剖面,对于文中的数据来说,重构的均方根误差可达到0.872 m/s;增加经验正交函数的阶数能提高重构精度,但5阶以上,阶数的继续增加对精度的提高将不会有显著的影响。     

Spectrally constrained chromophore and scattering near-infrared tomography provides quantitative and robust reconstruction

A multispectral direct chromophore and scattering reconstruction technique has been implemented for near-infrared frequency-domain tomography in recovering images of total hemoglobin, oxygen saturation, water, and scatter parameters. The method applies the spectral constraint of the chromophores and scattering spectra directly in the reconstruction algorithm, thereby reducing the parameter space of the inversion process. This new method was validated by use of simulated and experimental data, and results show better robustness and stability in the presence of higher levels of noise. The method suppresses artifacts, especially those significant in water and scatter power images, and reduces cross talk between chromophore and scatter parameters. Variation in scattering was followed by this spectral approach successfully in experimental data from 90-mm-diameter cylindrical phantoms, and results show linear variation in scatter amplitude and reduced scattering coefficient (micro(s)'), with total hemoglobin, oxygen saturation, and water remaining constant and quantitatively accurate. Similar experiments were carried out for varying oxygen saturation and total hemoglobin. Accurate quantification was obtained with a mean error of 7.7% for oxygen saturation and 6.2% for total hemoglobin, with minimal cross talk between different parameters.     

Enhanced frequency-domain optical image reconstruction in tissues through total-variation minimization

Optical image reconstruction in heterogeneous turbid media is sensitive to noise, especially when the signal-to-noise ratio of a measurement system is low. A total-variation-minimization-based iterative algorithm is described in this paper that enhances the quality of reconstructed images with frequency-domain data over that obtained previously with a regularized least-squares approach. Simulation experiments in an 8.6-cm-diameter circular heterogeneous region with low- and high-contrast levels between the target and the background show that the quality of the reconstructed images can be improved considerably when total-variation minimization is included. These simulated results are further verified and confirmed by images reconstructed from experimental data by the use of the same geometry and optically tissue-equivalent phantoms. Measures of imaging performance, including the location, size, and shape of the reconstructed heterogeneity, along with absolute errors in the predicted optical-property values are used to quantify the enhancements afforded by this new approach to optical image reconstruction with diffuse light. The results show improvements of up to 5 mm in terms of geometric information and an order of magnitude or more decrease in the absolute errors in the reconstructed optical-property values for the test cases examined.     

Fiber-optic probe for noninvasive real-time determination of tissue optical properties at multiple wavelengths

We present a compact, fast, and versatile fiber-optic probe system for real-time determination of tissue optical properties from spatially resolved continuous-wave diffuse reflectance measurements. The system collects one set of reflectance data from six source-detector distances at four arbitrary wavelengths with a maximum overall sampling rate of 100 Hz. Multivariate calibration techniques based on two-dimensional polynomial fitting are employed to extract and display the absorption and reduced scattering coefficients in real-time mode. The four wavelengths of the current configuration are 660, 785, 805, and 974 nm, respectively. Cross-validation tests on a 6 x 7 calibration matrix of Intralipid-dye phantoms showed that the mean prediction error at, e.g., 785 nm was 2.8% for the absorption coefficient and 1.3% for the reduced scattering coefficient. The errors are relative to the range of the optical properties of the phantoms at 785 nm, which were 0-0.3/cm for the absorption coefficient and 6-16/cm for the reduced scattering coefficient. Finally, we also present and discuss results from preliminary skin tissue measurements.     

Optical property measurements of turbid media in a small-volume cuvette with frequency-domain photon migration

A frequency-domain photon migration (FDPM) technique is developed for quantitative measurement of the absorption and reduced scattering coefficients of highly turbid samples in a small-volume (0.45-ml) reflective cuvette. We present both an analytical model for the FDPM cuvette and its experimental verification, using calibrated phantoms and suspensions of living cells. FDPM model fits to experimental data demonstrate that the reduced scattering (mu(s)?) and absorption (mu(a)) coefficients can be derived with accuracies of 5-10% and 10-15%, respectively. Changing the cuvette wall reflectivity alters the frequency-dependent behavior of photon density waves (PDWs). For highly reflective wall boundaries (R(eff) >/= 90-95%), PDW confinement leads to substantial enhancement in both amplitude and phase compared with identical samples in infinite media. Results from experiments on microsphere suspensions are compared with predictions from Mie theory to assess the potential of this method to interpret scattering properties in terms of scatterer size and density. Optical property measurements of biological cell suspensions are reported, and the possibility of optically monitoring cell physiology in a carefully controlled environment is demonstrated.     

Two-dimensional Kerr-Fourier imaging of translucent phantoms in thick turbid media

Translucent scattering phantoms hidden inside a 5.5-cm-thick Intralipid solution were imaged as a function of phantom scattering coefficients by the use of a picosecond time- and space-gated Kerr-Fourier imaging system. A 2-mm-thick translucent phantom with a 0.1% concentration (scattering coefficient) difference from the 55-mm-thick surrounding scattering host can be distinguished at a signal level of ~10(-10) of the incidence illumination intensity.     

Simultaneous extraction of optical transport parameters and intrinsic fluorescence of tissue mimicking model media using a spatially resolved fluorescence technique

We present a method based on spatially resolved fluorescence measurement for the simultaneous estimation of optical transport parameters, namely, the reduced scattering coefficient (micro s'), the absorption coefficient (micro a), and the intrinsic fluorescence spectra from turbid media. The accuracy of this approach was tested by conducting studies on a series of tissue-simulating phantoms with known optical transport properties. The estimated relative error in the values for micro s' and micro a using this technique was found to be < or =10%. Furthermore, the line shape and intensity of the intrinsic fluorescence recovered by using this approach were observed to be free from the distorting effects of the wavelength-dependent absorption and scattering properties of the medium, and they were in excellent agreement with the directly measured intrinsic fluorescence spectra of the fluorophores.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part I: Theory and validation on synthetic phantoms

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption (0-20 cm(-1)) and reduced scattering coefficients (7-33 cm(-1)). Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of 350-850 nm. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of 3% or less for phantoms containing hemoglobin and 12% or less for phantoms containing Nigrosin.