伪双能X射线透射系统矫正厚度影响的物质鉴别方法

X射线透视技术已被证实是一种非常有效的安全检查方法.基于这种技术的伪双能X射线透射系统广泛应用于车站、机场等重要场所.伪双能系统的射线源产生的是连续能谱的X射线,因此基于传统双能透射模型的物质鉴别方法由于受到物体的厚度影响而导致准确性的降低.在根据高低能信号的对数比值的基础上,引入X射线的衰减因素到物质属性特征空间中,研究出矫正厚度影响的鉴别方法.实验结果证明在高维特征空间中的物质鉴别方法能够有效提高鉴别结果的准确性.     

现代通信传输接入技术分析

经济社会建设为科学技术发展营造了良好的外部环境,通信行业亦是如此。通信传输与接入技术作为信息技术中的核心,在工业运输等领域发挥着重要作用。结合我国通信行业的发展情况来看,自动交换网络等现代通信传输技术得到了广泛的应用与推广,在改善人们物质生活的方面发挥了重要作用。文中结合我国现代通信技术的实际发展,对常见的通信传输接入技术展开了研究与分析,旨在推动通信行业的转型与升级。     

Effects of scatter in dual-energy imaging: an alternative analysis

Dual-energy imaging provides images in which the conspicuity of the signal of interest is heightened by selectively cancelling intervening structures. Area detectors for dual-energy imaging offer some advantages over line-scanning systems because they make efficient use of the source. Area detectors, however, collect scattered radiation. To determine the seriousness of the scatter problem and how effective scatter correction is at reducing scatter's deleterious effects, dual-energy imaging in the presence of scatter is simulated. The coefficients are modified so that the intervening material and the scatter are cancelled in some particular region of the image. Results for simulations of two clinically important material-subtraction-the bone-subtraction image and the soft-tissue-subtraction image-are presented. The effects of scatter on contrast, noise variance, and SNR for the two subtractions are examined.     

The problem of scatter correction in positron volume imaging

Thin, dense interslice septa have long been used to reduce the scattered radiation collected in positron emission tomography (PET). These septa prevent the acquisition of coincident gamma rays that are oblique to the scanning planes. Several volume imaging systems that acquire oblique rays have been built. The reasons why the scatter fraction is intrinsically higher in these systems are discussed, and two different scatter compensation techniques are compared. The comparison uses Monte Carlo simulations to generate average profiles and spectra for typical phantoms and scanning geometries. Comparison results indicate that deconvolution of the total event profiles with a filter adjusted to the object size and good energy discrimination provide an excellent scatter estimate as long as the object's diameter is less than the detector's radius. The profiles derived from a second, lower, energy window are always much flatter than the scattered counts in a window covering the photopeak. They do not match the scattered event profile and are less reliable, being based on a lower number of counts.     

Locating objects in wide-area systems

Locating mobile objects in a worldwide system requires a scalable location service. An object can be a telephone or a notebook computer, but also a software or data object, such as a file or an electronic document. Our service strictly separates an object's name from the addresses where it can be contacted. This is done by introducing a location-independent object handle. An object's name is bound to its unique object handle, which, in turn, is mapped to the addresses where the object can be contacted. To locate an object, we need only its object handle. We present a scalable location service based on a worldwide distributed search tree that adapts dynamically to an object's migration pattern to optimize lookups and updates     

X-Ray Backscatter Imaging

This paper describes a new type of X-ray Compton scatter imaging technique which has potential application to medical diagnostic radiography. This system detects the Compton interacted radiation which is scattered back toward the X-ray source and uses the information to generate an interior view of an object from a frontal backprojection imaging perspective. X-ray scatter radiographs can provide a three-dimensional imaging ability that is different from computerized axial tomography and may provide additional medical diagnostic information which is difficult or expensive to derive from conventional techniques.     

Sensitivity of photon-counting based K-edge imaging in X-ray computed tomography

The feasibility of K-edge imaging using energy-resolved, photon-counting transmission measurements in X-ray computed tomography (CT) has been demonstrated by simulations and experiments. The method is based on probing the discontinuities of the attenuation coefficient of heavy elements above and below the K-edge energy by using energy-sensitive, photon counting X-ray detectors. In this paper, we investigate the dependence of the sensitivity of K-edge imaging on the atomic number Z of the contrast material, on the object diameter D , on the spectral response of the X-ray detector and on the X-ray tube voltage. We assume a photon-counting detector equipped with six adjustable energy thresholds. Physical effects leading to a degradation of the energy resolution of the detector are taken into account using the concept of a spectral response function R(E,U) for which we assume four different models. As a validation of our analytical considerations and in order to investigate the influence of elliptically shaped phantoms, we provide CT simulations of an anthropomorphic Forbild-Abdomen phantom containing a gold-contrast agent. The dependence on the values of the energy thresholds is taken into account by optimizing the achievable signal-to-noise ratios (SNR) with respect to the threshold values. We find that for a given X-ray spectrum and object size the SNR in the heavy element's basis material image peaks for a certain atomic number Z. The dependence of the SNR in the high- Z basis-material image on the object diameter is the natural, exponential decrease with particularly deteriorating effects in the case where the attenuation from the object itself causes a total signal loss below the K-edge. The influence of the energy-response of the detector is very important. We observed that the optimal SNR values obtained with an ideal detector and with a CdTe pixel detector whose response, showing significant tailing, has been determined at a synchrotron differ by factors of about two to three. The potentially very important impact of scattered X-ray radiation and pulse pile-up occurring at high photon rates on the sensitivity of the technique is qualitatively discussed.     

X-Ray Compton Scatter Imaging Using a High Speed Flying Spot X-Ray Tube

A system of Compton scatter medical X-ray fluoroscopy is investigated in this research which uses a specially constructed flying spot X-ray tube. The imaging system uses a narrow pinpoint X-ray beam which scans an object in near real time and creates a penetrating frontal view radiograph of variable penetration into the object. The results of our initial work with X-ray Compton backscatter imaging were presented in a previous paper, and this research seeks to demonstrate an improved X-ray generator which allows the radiographs to be produced much more rapidly. One application of the system may be to provide an X-ray frontal backprojection view of the moving heart epicardial surface which could be useful as a noninvasive diagnostic of cardiac function.     

Scatter correction method for X-ray CT using primary modulation: theory and preliminary results

An X-ray system with a large area detector has high scatter-to-primary ratios (SPRs), which result in severe artifacts in reconstructed computed tomography (CT) images. A scatter correction algorithm is introduced that provides effective scatter correction but does not require additional patient exposure. The key hypothesis of the algorithm is that the high-frequency components of the X-ray spatial distribution do not result in strong high-frequency signals in the scatter. A calibration sheet with a checkerboard pattern of semitransparent blockers (a "primary modulator") is inserted between the X-ray source and the object. The primary distribution is partially modulated by a high-frequency function, while the scatter distribution still has dominant low-frequency components, based on the hypothesis. Filtering and demodulation techniques suffice to extract the low-frequency components of the primary and hence obtain the scatter estimation. The hypothesis was validated using Monte Carlo (MC) simulation, and the algorithm was evaluated by both MC simulations and physical experiments. Reconstructions of a software humanoid phantom suggested system parameters in the physical implementation and showed that the proposed method reduced the relative mean square error of the reconstructed image in the central region of interest from 74.2% to below 1%. In preliminary physical experiments on the standard evaluation phantom, this error was reduced from 31.8% to 2.3%, and it was also demonstrated that the algorithm has no noticeable impact on the resolution of the reconstructed image in spite of the filter-based approach. Although the proposed scatter correction technique was implemented for X-ray CT, it can also be used in other X-ray imaging applications, as long as a primary modulator can be inserted between the X-ray source and the imaged object.     

Sharpening filter for false color imaging of dual-energy X-ray scans

Dual-energy X-ray imaging has a vast range of application in security. Luggage inspection is an essential process for an airplane or court house security as well as securing mass events. An image of a content of some package may help to figure out if there is any dangerous object inside and avoid possibly threatening situation. As the raw X-ray images are not always easy to analyze and interpret, some image processing methods like an object detection, a frequency resolution increase or a pseudocoloring are being used. Since color can be a powerful tool to improve the usefulness of an information display, we propose pseudocoloring improvement by modifying material-based approach with edge detection to fill and sharpen color layers over the image making it easier to read and analyze. We demonstrate the effectiveness of the methods using real data, acquired from a professional dual-energy X-ray scanner.     

Energy dependence of nonstationary scatter subtraction--restoration in high resolution PET

In previous works, the determination of object and detector scatter kernels from line source measurements was described and their application in scatter correction was investigated. It was also shown that low energy data contains a large fraction of useful events (true and detector scatter events). In the present work, data acquired in multispectral mode was summed in single broad energy windows of lower energy thresholds varying from 129 to 516 keV in steps of 43 keV and a constant upper energy threshold of 645 keV. Line-source projections were fitted by extracting the object and detector scatter kernels as a function of energy threshold. These kernels were then used to process scatter by the nonstationary convolution subtraction-restoration method in phantom images. After scatter correction, the sensitivity is found to increase by up to 64% at the lower threshold of 129 keV, relative to the conventional photopeak energy window (344-645 keV). Whereas contrast and spatial resolution are degraded as the energy discriminator is lowered, such degradation is fully recovered by the scatter correction. As a result of scatter correction, the noise increases insignificantly in hot regions but substantially in cold regions, in proportion of the amount of scatter.     

基于MSR和融合理论的X射线安检图像增强算法

针对X射线安检图像噪声大、对比度低和边缘不清晰等问题,提出一种结合多尺度Retinex算法(Multi-Scale Ret-inex,MSR)算法和图像灰度最大值融合的双重能量X射线图像增强算法.首先,应用MSR算法对高能和低能X射线图像进行处理得到初步增强结果,然后采用空域灰度值最大融合算法融合经过MSR算法初步增强后的高能和低能X射线图像从而得到最终增强X射线图像.实验结果表明该算法能更有效地提高双重能量X射线图像的对比度,显著改善图像质量.     

灰度掩模等级的精确控制研究

在基于空间光调制器(SLM)的灰度掩模并行制作方法中,基于曝光曲线的线性近似关系,建立了灰度掩模强度透过率的线性近似模型,给出了灰度掩模等级精度的精确控制策略.利用卤化银全息感光材料进行了相关实验,制作了菲涅耳透镜的2阶、8阶和16阶灰度掩模.分析了灰度掩模的边缘模糊效应误差,提出了克服非线性效应对灰度等级精度影响的初步方法.     

Energy dependence of scatter components in multispectral PET imaging

High resolution images in PET based on small individual detectors are obtained at the cost of low sensitivity and increased detector scatter. These limitations can be partially overcome by enlarging discrimination windows to include more low-energy events and by developing more efficient energy-dependent methods to correct for scatter radiation from all sources. The feasibility of multispectral scatter correction was assessed by decomposing response functions acquired in multiple energy windows into four basic components: object, collimator and detector scatter, and trues. The shape and intensity of these components are different and energy-dependent. They are shown to contribute to image formation in three ways: useful (true), potentially useful (detector scatter), and undesirable (object and collimator scatter) information to the image over the entire energy range. With the Sherbrooke animal PET system, restoration of detector scatter in every energy window would allow nearly 90% of all detected events to participate in image formation. These observations suggest that multispectral acquisition is a promising solution for increasing sensitivity in high resolution PET. This can be achieved without loss of image quality if energy-dependent methods are made available to preserve useful events as potentially useful events are restored and undesirable events removed.     

Improved SPECT quantitation using fully three-dimensional iterative spatially variant scatter response compensation

The quality and quantitative accuracy of iteratively reconstructed SPECT images improves when better point spread function (PSF) models of the gamma camera are used during reconstruction. Here, inclusion in the PSF model of photon crosstalk between different slices caused by limited gamma camera resolution and scatter is examined. A three-dimensional (3-D) projector back-projector (proback) has been developed which models both the distance dependent detector point spread function and the object shape-dependent scatter point spread function of single photon emission computed tomography (SPECT). A table occupying only a few megabytes of memory is sufficient to represent this scatter model. The contents of this table are obtained by evaluating an analytical expression for object shape-dependent scatter. The proposed approach avoids the huge memory requirements of storing the full transition matrix needed for 3-D reconstruction including object shape-dependent scatter. In addition, the method avoids the need for lengthy Monte Carlo simulations to generate such a matrix. In order to assess the quantitative accuracy of the method, reconstructions of a water filled cylinder containing regions of different activity levels and of simulated 3-D brain projection data have been evaluated for technetium-99m. It is shown that fully 3-D reconstruction including complete detector response and object shape-dependent scatter modeling clearly outperforms simpler methods that lack a complete detector response and/or a complete scatter response model. Fully 3-D scatter correction yields the best quantitation of volumes of interest and the best contrast-to-noise curves.     

基于MES的T/R组件批生产技术

介绍了针对T/R组件批生产技术研究开发的制造执行系统MES,该系统与自动化物流系统相结合,突破了批生产中涉及的产品工艺、计划、物料、质量跟踪等各项关键技术。详细介绍了MES基础资料管理、物料及配送管理、生产计划管理、现场作业管理、综合统计查询等主要功能,并着重阐述了基于关键元器件的质量追溯技术。最后结合典型产品介绍了MES在XXX型T/R组件制造过程中的应用。     

Triangle impulse response (TIR) calculation for lossy transmission line simulation

Triangle impulse responses (TIRs) for lossy transmission lines are accurately calculated using both an inverse fast Fourier transform algorithm and an accelerated inverse Laplace transform algorithm. Frequency dependent transmission line parameters, i.e., R, L, G, and C, are employed to model the skin effect and the frequency dependent electrical properties of the substrate material. The calculated TIR can be further used to carry out time domain simulations for a large number of lossy transmission lines. Frequency dependent line parameters, R, L, G, and C should be used in specific cases to assure the causality of signal waveform, the accuracy of the time delay, and the amplitude of the waveform evaluations in the time domain.     

空间目标宽带雷达特征信号仿真建模

空间目标宽带雷达特征信号包括其高分辨一维距离像和二维ISAR图像,空间目标宽带雷达特征信号仿真建模对空间目标探测、识别研究具有重要意义。在光学区复杂目标RCS特征信号计算基础上,重点研究了空间目标宽带雷达特征信号包括高分辨一维距离像和二维ISAR图像仿真建模方法。仿真目标和实际复杂空间目标宽带雷达特征信号仿真建模的实验结果验证了其有效性。     

毫米波有源相控阵TR组件集成技术

通过分析有源相控阵技术发展趋势,提出集成技术是毫米波有源相控阵TR组件的关键技术,并按制造和装配层次将毫米波有源相控阵TR组件的集成分为芯片级、子阵级和全阵级等三级集成.分析了各级集成的关键技术及其发展趋势,提出关键集成技术发展路线,指出毫米波TR组件专用多功能芯片、垂直互联和高效小型化液冷器等三项技术是当前需重点突破...     

5MW海上风力发电机组关键技术浅析

本文主要介绍了5MW海上风力发电机组研发过程中涉及到的一些关键技术,主要包括变流器、发电机、齿轮箱、控制系统、输电技术、并网技术、叶片、塔架等关键技术。此外．本文还简单介绍了风机基础和安装过程中涉及到的一些技术,为研发海上风力发电机组提供了参考。