用高分辨工业X—CT检测陶瓷样品

清华大学核能技术设计研究院自８０年代中开始到８０年代中的十年来建成了三个微焦点Ｘ－ＣＴ系统。本文介绍了采用闪烁体－光电二级管阵列高分辩探测器的ＣＴ系统硬件结构和图像重建中的“拆线近似法”技术,给出了用该系统检测若干陶瓷样品的结果。     

单电子脉冲的多道快速检测

采用MCP、光子学传输、计算机控制光电二极管阵列构成了可用于电子谱的多道检测系统。与一般光谱探测器不同，该系统在单电子脉冲计数方式下工作，与计算机适配性好，并有极低的检测下限。曾设计了放大、采样保持、阈值辨别以及移位寄存等硬件电路和以并行采集、真伪判别为主的软件程序。软件划分64像素为16道，以1000～7140次/s的频率扫描，饱和计数率可高达105次/s。同时给出该系统初步的实验结果，对此探测器在实际X射线光电子能谱仪中应用的优越性作了评论。     

一种工业CT数字成像检测系统扫描时间的计算方法

针对当今对工业CT数字成像检测系统检测效率的要求,提出一种工业CT数字成像检测系统扫描时间的计算方法,研究工业CT数字成像检测系统不同扫描模式下扫描时间与探测器工艺参数的关系,获取扫描时间与探测器工艺参数的关系表达式,实现扫描时间的定量表示,为合理安排检测工作具有指导作用。     

基于SPD的物体色快速分光测试系统设计

根据光度学与色度学理论，采用国际照明委员会（CIE）推荐的d/8标准照明／观察几何条件，应用自扫描光电二极管阵列（SPD）作为乐电探测器，设计了由积分球，脉冲光源，多色仪，光电放大与A／D转换器以及专用计算机等部分组成的双光路多通道物体表面色全光谱快速测试系统，该系统单次测色周期小于1秒，对陶瓷白板的测量精度（色度坐标）优于0．0003，重复性达到0．0001，满足了快速又准确的分光测色要求。     

光纤阵列成像激光雷达系统的设计

简要介绍了光纤阵列成像激光雷达的研究背景、系统优势和发展现状.然后提出了本文设计的雷达系统,并介绍了该系统的工作原理,系统采用光纤阵列前端窗口扫描的方法,避免了光电探测器阵列的制作,同时减少了光电探测器的数量.之后文章对光纤阵列成像激光雷达系统的各部分器件进行分析,包括光纤的选择、光纤阵列的设计和聚焦透镜的分析,并重点讨论了聚焦透镜F值对光纤阵列接收系统的影响,最终得到本系统聚焦透镜F最优值5.47.最后推导了本文光纤阵列成像激光雷达系统的传输效率,给出了传输效率公式.     

单电子脉冲的多道快速检测

采用ＭＣＰ、光子学传输、计算机控制光电二极管阵列构成了可用于电子谱的多道检测系统。与一般光谱探测器不同，该系统在单电子脉冲计数下工作，与计算机适配性好，并有极低的检测下限，曾设计了放大、采样保持、阈值辨别以及移位寄存等硬件电路和以并行采集、真伪判别为主的软件程序。软件发６４像素为１６道。以１０００－－７１４０次／ｓ的频率扫描，饱和计数率可高达１０＾５次／ｓ。同时给出该系统初步的实验结果，对此探测顺     

位置敏感探测器定位分析和应用研究

位置敏感探测器是近几年问世的一种新型位置探测器,可直接用来测量角度、高度、距离及运动。本文论证了二维位置敏感探测器定位原理,导出了位置坐标的电流函数表达式,给出了相应的检测电路框图,提出了用位置敏感探测器进行人体三维运动测量的系统方案,并就信号的产生、提取及数据处理问题进行了讨论,最后估算了有关系统参数。     

LuAG:Ce,Mg闪烁陶瓷的X射线平板探测器成像研究

采用固相反应法结合真空烧结技术制备了具有高光学质量高闪烁效率的(Lu,Ce,Mg)3Al5O12(LuAG:0.3at%Ce,0.2at%Mg)闪烁陶瓷。将20 mm×20 mm×0.05 mm的陶瓷薄片用含有石墨粉的硅胶粘接在尺寸为25 mm×25 mm×4 mm的石墨基底上,再激光加工切割成50μm×50μm、间距10μm的正方形阵列,进行X射线平板探测器成像研究,并分别采用铅线对卡法和刀口法对陶瓷闪烁探测器的成像质量进行表征。结果表明:陶瓷闪烁体制备的平板探测器成像清晰锐利,铅线对卡法测试激光切割样品10 lp/mm下MTF可达17.5%。刀口法测试激光切割样品MTF为10%时,分辨率可达9 lp/mm。该闪烁陶瓷具有在平板探测器上应用的潜力。     

400um像素X射线阵列探测器的设计

描述了由美国X-SCAN公司生产的400um像素大小的X射线阵列探测器系统的设计,此探测器系统集信号探测、模拟信号放大、数字信号处理与输出于一体,有多种控制功能可供选择,可方便地与计算机连接,实现图像或信号的数字化处理。可广泛的应用于各种无损检测领域。     

H—S法波前探测的高速图象采集系统

自适应光学系统中有两种方法用于测定波前的局部斜率：剪切干涉测量法和哈特曼法（以下简称Ｈ－Ｓ法）。由于Ｈ－Ｓ法运用较简单的光学系统，无需任何活动组件，具有较高的光效率，并能很好地用于探测器阵列，因此它更普遍地用于自适应光学系统中。本文介绍了一种应用于Ｈ－Ｓ法波前探测的高速图象采集系统，提出了应用本图象采集系统解决高帧频探测器阵列与数据处理机之间的同步协调的方法。     

高能 X 射线工业 CT 技术的研究进展

目的 研究分析了国内外高能X射线工业CT技术的进展情况，方法 通过有关文献资料，对目前国际上主要的高能X射线工业CT技术及设备进行评述。结果和结论 对美国、德国等发达国家的高能X射线工业CT设备、线阵探测器、面陈探测器及重建算法进行了分析。     

网格投影式立体视觉三维表面重建系统

提出了一种基于立体视觉的三维表面重建的新方法。该方法以立体视觉为基础,结合网格投影,把被动的立体视觉与主动的非结构光网格投影相结合,采用一种算法简单的由粗到精网格图像立体匹配方法,有效地解决了常用的立体视觉系统中存在的算法复杂、处理时间长、容易产生误匹配等问题。基于该方法的三维表面重建系统具有结构简单、操作方便、数据采集速度快、实时性强等优点。实验结果表明该系统能够有效地对三维表面,特别是对无明显特征的光滑自由三维曲面进行重建。     

Semi-three-dimensional algorithm for time-resolved diffuse optical tomography by use of the generalized pulse spectrum technique

Although a foil three-dimensional (3-D) reconstruction with both 3-D forward and inverse models provide, the optimal solution for diffuse optical tomography (DOT), because of the 3-D nature of photon diffusion in tissue, it is computationally costly for both memory requirement and execution time in a conventional computing environment. Thus in practice there is motivation to develop an image reconstruction algorithm with dimensional reduction based on some modeling approximations. Here we have implemented a semi-3-D modified generalized pulse spectrum technique for time-resolved DOT, where a two-dimensional (2-D) distribution of optical properties is approximately assumed, while we retain 3-D distribution of photon migration in tissue. We have validated the proposed algorithm by reconstructing 3-D structural test objects from both numerically simulated and experimental date. We demonstrate our algorithm by comparing it with the calibrated 2-D reconstruction that is in widespread use as a shortcut to 3-D imaging and proving that the semi-3-D algorithm outperforms the calibrated 2-D algorithm.     

Optical tomographic image reconstruction from ultrafast time-sliced transmission measurements

Optical imaging and localization of objects inside a highly scattering medium, such as a tumor in the breast, is a challenging problem with many practical applications. Conventional imaging methods generally provide only two-dimensional (2-D) images of limited spatial resolution with little diagnostic ability. Here we present an inversion algorithm that uses time-resolved transillumination measurements in the form of a sequence of picosecond-duration intensity patterns of transmitted ultrashort light pulses to reconstruct three-dimensional (3-D) images of an absorbing object located inside a slab of a highly scattering medium. The experimental arrangement used a 3-mm-diameter collimated beam of 800-nm, 150-fs, 1-kHz repetition rate light pulses from a Ti:sapphire laser and amplifier system to illuminate one side of the slab sample. An ultrafast gated intensified camera system that provides a minimum FWHM gate width of 80 ps recorded the 2-D intensity patterns of the light transmitted through the opposite side of the slab. The gate position was varied in steps of 100 ps over a 5-ns range to obtain a sequence of 2-D transmitted light intensity patterns of both less-scattered and multiple-scattered light for image reconstruction. The inversion algorithm is based on the diffusion approximation of the radiative transfer theory for photon transport in a turbid medium. It uses a Green s function perturbative approach under the Rytov approximation and combines a 2-D matrix inversion with a one-dimensional Fourier-transform inversion to achieve speedy 3-D image reconstruction. In addition to the lateral position, the method provides information about the axial position of the object as well, whereas the 2-D reconstruction methods yield only lateral position.     

Automatic multiscale meshing through HRBF networks

A procedure for the real-time construction of three-dimensional (3-D) multiscale meshes from not evenly sampled 3-D points is described and discussed in this paper. The process is based on the connectionist model named hierarchical radial basis functions network (HRBF), which has been proved effective in the reconstruction of smooth surfaces from sparse noisy data points. The network goal is to achieve a uniform reconstruction error, equal to measurement error, by stacking noncomplete grids of Gaussians at decreasing scales. It is shown here how the HRBF properties can be used to develop a configuration algorithm, which produces a continuous surface in real time. In addition, the model is extended to automatically convert the continuous surface into a 3-D mesh according to an adequate error measure.     

Simultaneous mapping of absorption and scattering coefficients from a three-dimensional model of time-resolved optical tomography

A Newton-Raphson inversion algorithm has been extended for simultaneous absorption and scattering reconstruction of fully three-dimensional (3D) diffuse optical tomographic imaging from time-resolved measurements. The proposed algorithm is derived from the efficient computation of the Jacobian matrix of the forward model and uses either the algebraic reconstruction technique or truncated singular-value decomposition as the linear inversion tool. Its validation was examined with numerically simulated data from 3-D finite-element discretization models of tissuelike phantoms, with several combinations of geometric and optical properties, as well as two commonly used source-detector configurations. Our results show that the fully 3-D image reconstruction of an object can be achieved with reasonable quality when volumetric light propagation in tissues is considered, and temporal information from the measurements can be effectively employed. Also, we investigated the conditions under which 3-D issues could be approximately addressed with two-dimensional reconstruction algorithms and further demonstrated that these conditions are seldom predictable or attainable in practice. Thus the application of 3-D algorithms to realistic situations is necessary.     

Robust 3-D Motion Tracking From Stereo Images: A Model-Less Method

Traditional vision-based 3-D motion-estimation algorithms require given or calculated 3-D models while the motion is being tracked. We propose a high-speed extended-Kalman-filter-based approach that recovers camera position and orientation from stereo image sequences without prior knowledge, as well as the procedure for the reconstruction of 3-D structures. Empowered by the use of a trifocal tensor, the computation step of 3-D models can be eliminated. The algorithm is thus flexible and can be applied to a wide range of domains. The twist motion model is also adopted to parameterize the 3-D motion. It is minimal since it only has six parameters as opposed to seven parameters in quaternion and 12 parameters in matrix representation. The motion representation is robust because it does not suffer from singularities as Euler angles. Due to the fact that the number of parameters to be estimated is reduced, our algorithm is more efficient, stable, and accurate than traditional approaches. The proposed method has been applied to recover the motion from stereo image sequences taken by a robot and a handheld stereo rig. The results are accurate compared to the ground truths. It is shown in the experiment that our algorithm is not susceptible to outlying point features with the application of a validation gate.     

Electrical Capacitance Volume Tomography

A dynamic volume imaging based on the principle of electrical capacitance tomography (ECT), namely, electrical capacitance volume tomography (ECVT), has been developed in this study. The technique generates, from the measured capacitance, a whole volumetric image of the region enclosed by the geometrically three-dimensional capacitance sensor. This development enables a real-time, 3-D imaging of a moving object or a real-time volume imaging (4-D) to be realized. Moreover, it allows total interrogation of the whole volume within the domain (vessel or conduit) of an arbitrary shape or geometry. The development of the ECVT imaging technique primarily encloses the 3-D capacitance sensor design and the volume image reconstruction technique. The electrical field variation in three-dimensional space forms a basis for volume imaging through different shapes and configurations of ECT sensor electrodes. The image reconstruction scheme is established by implementing the neural-network multicriterion optimization image reconstruction (NN-MOIRT), developed earlier by the authors for the 2-D ECT. The image reconstruction technique is modified by introducing into the algorithm a 3-D sensitivity matrix to replace the 2-D sensitivity matrix in conventional 2-D ECT, and providing additional network constraints including 3-to-2-D image matching function. The additional constraints further enhance the accuracy of the image reconstruction algorithm. The technique has been successfully verified over actual objects in the experimental conditions     

Study on Generalized Analysis Model for Fringe Pattern Profilometry

This paper presents a generalized analysis model for fringe pattern profilometry. We mathematically derived a new analysis model that gives a more general expression of the relationship between projected and deformed fringe patterns. Meanwhile, based on the proposed generalized model, a new algorithm is presented to retrieve 3-D surfaces from nonlinearly distorted fringes. Without any prior knowledge about the projection system, we still can obtain very accurate measurement results by using a generalized analysis model and a proposed algorithm. Computer simulation and experimental results show that the generalized model and the proposed algorithm can significantly improve the 3-D reconstruction precision, especially when the projected fringe pattern is nonlinearly distorted.     

Gradient-Vector-Flow Snake Method for Quantitative Image Reconstruction Applied to Mandibular Distraction Surgery

To improve planning of maxillofacial surgery, a novel method for maxillary-, mandibular-, and facial-nerve 3-D image reconstruction was implemented and optimized. A set of images acquired by a computed tomography (CT) scanner was segmented to reconstruct the 3-D model of the maxilla and mandible. Particular attention was given to the segmentation of the facial nerve, which was obtained through the gradient-vector-flow (GVF) snake method. After segmentation, precise anatomical 3-D plastic models were fabricated through stereolithography from CT scans of five clinical cases that will undergo either dental implant surgery or bone distraction. For all cases, 3-D models delivered essential visual and tactile information for the planning and simulation of surgery as well as for customized implant preparation.