An algorithm for computed tomography image reconstruction from limited-view projections

With the development of the compressive sensing theory, the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology. This paper develops an iterative algorithm for image reconstruction, which can fit the most cases. This method gives an image reconstruction flow with the difference image vector, which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough. Then the l1-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles. The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data. Moreover, all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed.

Image Reconstruction from Fan-Beam Projections without Back-Projection Weight in a 2-D Dynamic CT: Compensation of Time-Dependent Rotational, Uniform Scaling and Translational Deformations

In a dynamic CT, the acquired projections are corrupted due to strong dynamic nature of the object, for example: lungs, heart etc. In this paper, we present fan-beam reconstruction algorithm without position-dependent backprojection weight which compensates for the time-dependent translational, uniform scaling and rotational deformations occurring in the object of interest during the data acquisition process. We shall also compare the computational cost of the proposed reconstruction algorithm with the existing one which has position-dependent weight. To accomplish the objective listed above, we first formulate admissibility conditions on deformations that is required to exactly reconstruct the object from acquired sequential deformed projections and then derive the reconstruction algorithm to compensate the above listed deformations satisfying the admissibility conditions. For this, 2-D time-dependent deformation model is incorporated in the fan-beam FBP reconstruction algorithm with no backprojection weight, assuming the motion parameters being known. Finally the proposed reconstruction algorithm is evaluated with the motion corrupted projection data simulated on the computer.

3D Face Reconstruction from a Single Image Using a Combined PCA-LPP Method

In this paper, we proposed a combined PCA-LPP algorithm toimprove 3D face reconstruction performance. Principal component analysis(PCA) is commonly used to compress images and extract features. Onedisadvantage of PCA is local feature loss. To address this, various studies haveproposed combining a PCA-LPP-based algorithm with a locality preservingprojection (LPP). However, the existing PCA-LPP method is unsuitable for3D face reconstruction because it focuses on data classification and clustering.In the existing PCA-LPP, the adjacency graph, which primarily shows the connectionrelationships between data, is composed of the e-or k-nearest neighbortechniques. By contrast, in this study, complex and detailed parts, such aswrinkles around the eyes and mouth, can be reconstructed by composing thetopology of the 3D face model as an adjacency graph and extracting localfeatures from the connection relationship between the 3D model vertices.Experiments verified the effectiveness of the proposed method. When theproposed method was applied to the 3D face reconstruction evaluation set,a performance improvement of 10% to 20% was observed compared with theexisting PCA-based method.

Soil Geochemistry Changes Induced by a Foreign Soil Reconstruction Project in Three Gorges Reservoir Region of China

Fertile topsoil was added onto the surface of barren slope land in Three Gorges Reservoir region of China in an anthropogenic process known as the foreign soil reconstruction project. The main goal of this paper was to reveal the influence of anthropogenic activities on pedogenic processes and soil classifications. Chemical weathering indices and comparative analysis were applied to discuss changes in geochemical compositions and weathering features of purplish soils(Cambisols) before and after the project. Results showed that:(1) The foreign soil reconstruction project slightly altered the major element composition of topsoil and improved the soil structure. Although the distributions of major elements in the original topsoil, original subsoil, foreign topsoil and newly constructed topsoil were all similar to that in upper continental crust, newly constructed topsoil was the most similar soil.(2) The chemical index of alteration was more sensitive than the weathering index of Parker at indicating chemical weathering status of purplish soil. The chemical weathering status of newly constructed topsoil was higher than that of the original topsoil and lower than that of foreign topsoil.(3) Anthropogenic activities may provide a promising new thought for the anthropogenic soil classification system. The scope and subgroups of Anthrosols should be extended and strengthened. Or there may be a need to combine Anthrosols and Technosols orders to create a new soil order. The results may be used for optimizing soil mellowing engineering activities and enriching the soil classification system.

Projects Lists Relating to Post-disaster Reconstruction

Aba Prefecture Company Name:Sichuan Xintong New Materials Co.Ltd. Address:Shuimo,Wenchuan Nature of Business:Private Project Name:Processing and Sale of Tourism Products Details:Producing and processing of Natural crystal products,man-made gem and other

Safety Management Strategies for Cross-railway Interchange Widening Project in Highway Reconstruction and Extension

Under the background of rapid social and economic development,the traffic volume of highways has increased,which has brought tremendous pressure to the old highways.In response to this situation,the original highway must be reconstructed and extended.It is necessary to focus on the analysis and exploration of the methods of interchange reconstruction and extension in current highway reconstruction and extension to avoid affecting normal traffic,as it will inevitably have an impact on the traffic operation environment.For this situation,it is necessary to analyze and understand the format and characteristics of traffic organization of the interchange operation area in time and propose corresponding safeguard measures.

Analysis of algebraic reconstruction technique for accurate imaging of gas temperature and concentration based on tunable diode laser absorption spectroscopy

An improved algebraic reconstruction technique（ART） combined with tunable diode laser absorption spectroscopy（TDLAS） is presented in this paper for determining two-dimensional（2D） distribution of H2O concentration and temperature in a simulated combustion flame.This work aims to simulate the reconstruction of spectroscopic measurements by a multi-view parallel-beam scanning geometry and analyze the effects of projection rays on reconstruction accuracy.It finally proves that reconstruction quality dramatically increases with the number of projection rays increasing until more than 180 for 20 × 20 grid,and after that point,the number of projection rays has little influence on reconstruction accuracy.It is clear that the temperature reconstruction results are more accurate than the water vapor concentration obtained by the traditional concentration calculation method.In the present study an innovative way to reduce the error of concentration reconstruction and improve the reconstruction quality greatly is also proposed,and the capability of this new method is evaluated by using appropriate assessment parameters.By using this new approach,not only the concentration reconstruction accuracy is greatly improved,but also a suitable parallel-beam arrangement is put forward for high reconstruction accuracy and simplicity of experimental validation.Finally,a bimodal structure of the combustion region is assumed to demonstrate the robustness and universality of the proposed method.Numerical investigation indicates that the proposed TDLAS tomographic algorithm is capable of detecting accurate temperature and concentration profiles.This feasible formula for reconstruction research is expected to resolve several key issues in practical combustion devices.

Three-dimensional reconstruction of human spinal cord based on histological serial sections

BACKGROUND： It is not possible to reconstruct the inner structure of the spinal cord, such as gray matter and spinal tracts, from the Visual Human Project database or CT and MRI databases, due to low image resolution and contrast in macrosection images. OBJECTIVE： To explore a semi-automatic computerized three-dimensional （3D） reconstruction of human spinal cord based on histological serial sections, in order to solve issues such as low contrast. DESIGN, TIME AND SETTING： An experimental study combining serial section techniques and 3D reconstruction, performed in the laboratory of Human Anatomy and Histoembryology at the Medical School of Nantong University during January to April 2008. SETTING： Department of Anatomy, Institute of Neurobiology, Jiangsu Province Key Laboratory of Neural Regeneration, Laboratory of Image Engineering. MATERIALS： A human lumbar spinal cord segment from fresh autopsy material of an adult male. METHODS： After 4% paraformaldehyde fixation for three days, serial sections of the lumbar spinal cord were cut on a Leica cryostat and mounted on slides in sequence, with eight sections aligned separately on each slide. All sections were stained with Luxol Fast Blue to reveal myelin sheaths. After gradient dehydration and clearing, the stained slides were coverslipped. Sections were observed and images recorded under a light microscope using a digital camera. Six images were acquired at x25 magnification and automatically stitched into a complete section image. After all serial images were obtained, 96 complete serial images of the human lumbar cord segment were automatically processed with ＂Curves＂, ＂Autocontrast＂, ＂Gray scale 8 bit＂, ＂Invert＂, ＂Image resize to 50%＂ steps using Photoshop 7.0 software. All images were added in order into 3D-DOCTOR 4.0 software as a stack, where serial images were automatically realigned with neighboring images and semi-automatically segmented for white matter and gray matter. Finally, simple surface and volume reconstruction were completed on a personal computer. The reconstructed human lumbar spinal cord segment was interactively observed, cut, and measured. MAIN OUTCOME MEASURES： The reconstructed human lumbar spinal cord segment. RESULTS： Compared with serial images obtained from other image modalities, such as CT, MRI, and macrosections from The Visual Human Project database, the Luxol Fast Blue stained histological serial section images exhibited higher resolution and contrast between gray and white matter. Image processing and 3D reconstruction steps were semi-automatically performed with related software. The 3D reconstructed human lumbar cord segment were observed, cut, and measured on a PC. CONCLUSION： A semi-automatically computerized method, based on histological serial sections, is an effective way to 3D-reconstruct the human spinal cord.

A FAST CONVERGING SPARSE RECONSTRUCTION ALGORITHM IN GHOST IMAGING

A fast converging sparse reconstruction algorithm in ghost imaging is presented. It utilizes total variation regularization and its formulation is based on the Karush-Kuhn-Tucker (KKT) theorem in the theory of convex optimization. Tests using experimental data show that, compared with the algorithm of Gradient Projection for Sparse Reconstruction (GPSR), the proposed algorithm yields better results with less computation work.

MULTIPARAMETER MEASUREMENT FOR RACEWAY GROOVE OF BEARING BASED ON 3D RECONSTRUCTION WITH DIGITAL STRUCTURED LIGHT

A fast 3D reconstruction method based on structured light to measure various parameters of the raceway groove is presented. Digital parallel grating stripes distributed with sine density are projected onto the raceway groove by a DLP projector, and distorting of stripes is happened on the raceway. Simultaneously, aided by three-step phase-shifting approach, three images covered by different stripes are obtained by a high-resolution CCD camera at the same location, thus a more accuracy local topography can be obtained. And then the bearing is rotated on a high precision computer controlled rotational stage. Three images are also obtained as the former step at next planned location triggered by the motor. After one cycle, all images information is combined through the mosaics. As a result, the 3D information of raceway groove can be gained. Not only geometric properties but also surface flaws can be extracted by software. A preliminary hardware system has been built, with which some geometric parameters have been extracted from reconstructed local topography.

Reduced aliasing artifacts using shaking projection k-space sampling trajectory

Radial imaging techniques, such as projection-reconstruction （PR）, are used in magnetic resonance imaging （MRI） for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion artifacts, and support fast imaging with short echo times. However, aliasing and streaking artifacts are two main sources which degrade radial imaging quality. For a given fixed number of k-space projections, data distributions along radial and angular directions will influence the level of aliasing and streaking artifacts. Conventional radial k-space sampling trajectory introduces an aliasing artifact at the first principal ring of point spread function （PSF）. In this paper, a shaking projection （SP） k-space sampling trajectory was proposed to reduce aliasing artifacts in MR images. SP sampling trajectory shifts the projection alternately along the k-space center, which separates k-space data in the azimuthal direction. Simulations based on conventional and SP sampling trajectories were compared with the same number projections. A significant reduction of aliasing artifacts was observed using the SP sampling trajectory. These two trajectories were also compared with different sampling frequencies. ASP trajectory has the same aliasing character when using half sampling frequency （or half data） for reconstruction. SNR comparisons with different white noise levels show that these two trajectories have the same SNR character. In conclusion, the SP trajectory can reduce the aliasing artifact without decreasing SNR and also provide a way for undersampling recon- struction. Furthermore, this method can be applied to three-dimensional （3D） hybrid or spherical radial k-space sampling for a more efficient reduction of aliasing artifacts.

Design Consideration and Reconstruction Method for Double-source Double-multislice Spiral CT

To accelerate the scan speed and improve the image quality, a new type of CT configuration, "double-source double-multislice spiral CT" (DSDMS-CT), which is based on two sets of single-source multislice spiral CT was proposed with a special reconstruction algorithm. Simulation results using the fan-beam filtered backprojection algorithm with a special interpolation method were presented for both single-source multislice spiral CT and DSDMS-CT. The results of new CT model show that it scans faster than the traditional spiral CT and has a better slice sensitivity profile (SSP) with larger pitch value.

A practical image reconstruction and processing method for symmetrically off-center detector CBCT system

CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial imaging.To cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the flat panel detector can be placed off-center horizontally.This scanning configuration extends the FOV effectively.However,each projection is transversely truncated,bringing errors and artifacts in reconstruction.In this paper,a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm.Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method.A novel CBCT system for maxillofacial imaging is used for clinical test,which is equipped with an off-center small size flat panel detector.Results show that reconstruction accuracy is acceptable for clinical use,and the image quality appears sufficient for specific diagnostic requirements.It provides a novel solution for clinical CBCT system,in order to reduce radiation dose and manufacturing cost.

Analytical image reconstruction methods in emission tomography

Data collected in two-dimensional projections give planar images of object at each projection angle. To obtain information along the depth of the object, tomographic images are reconstructed using these projections. There are basically two approaches to solve the problem of reconstruction: analytical and iterative, each one presenting its own advantages and limitations. This paper provides a detailed introduction and comparison to four analytical image reconstruction methods including Fourier transformation, simple back-projection, back-projection filtering and filtered back-projection.

Discussion on the Safe and Guaranteed Access of Interchange Widening in Reconstruction and Extension of Highway

In the process of reconstruction and extension of highways,the most important thing is to ensure that the overall level of the widening of interchanges is comprehensively improved to ensure safe traffic.However,due to the heavy and difficult tasks in the widening of interchanges,higher requirements are put forward for the construction quality of the project.In the actual construction of the project,it is necessary to actively analyze and explain the specific construction of the interchange widening project to ensure that the improvement level of the interchange widening in highway reconstruction and extension project is effectively upgraded.This paper gives a detailed introduction to the main construction technology for interchange widening project,clarifies the technical points of safety and guaranteed access,and proposes corresponding safeguard measures to ensure the comprehensive upgrade of the construction quality and standard of interchange widening in highway reconstruction and extension.

基于高维PDE投影恢复的低剂量CT重建方法

目的提出一种基于高维偏微分方程(PDE)投影恢复的低剂量CT重建方法。方法先将原始的投影数据映射到高维空间中,构造投影数据的高维表示,通过移动高维空间中的点来对高维表示进行更新,再使用偏微分方程对投影数据进行滤波,最后将恢复后的数据使用FBP算法重建出最终CT图像。结果在Shepp-Logan体模实验中,与FBP,PWLS-QM和TGV-WLS方法相比,新方法在相对均方根误差指标上分别降低了68.87%、50.15%和27.36%,结构相似性上分别提高了23.50%,8.83%和1.62%,特征相似性上分别提高了17.30%、2.71%和2.82%。在腹部临床数据实验中,与FBP,PWLS-QM和TGV-WLS方法相比,新方法在相对均方根误差中分别降低了42.09%、31.04%和21.93%,结构相似性上分别提高了18.33%、13.45%和4.63%,特征相似性上分别提高了3.13%、1.46%和1.10%。结论本研究提出的新方法在有效去除低剂量CT图像中的条形伪影和噪声的同时,可以保持图像的空间分辨率。

基于三维重建外点剔除的船舶航迹自适应修正

为了保证船舶的安全性,通过三维重建外点剔除进行船舶航迹自适应修正。采用均值限差法对船舶三维点云数据进行滤波处理,通过变窗口方差比值方法优化均值限差法,提升船舶三维点云滤波精度。针对滤波处理后的船舶三维点云数据,结合八叉树自适应网格对船舶进行三维重建,更准确地拟合船舶的表面形状。由此,在屏幕上投影八叉树自适应网格生成投影多边形,检测其与用户确定的矩形包围盒间的相交性,定义与矩形包围盒不相交的八叉树自适应网格内的点为外点,并将其剔除,可以更准确地计算船舶航行,完成船舶航迹自适应修正。实验结果表明,所提方法的点云滤波总误差控制在1.5%以内,可有效抑制海面杂波等因素造成的外点影响,且规划的航线与原定航线一致性较高,可以保证船舶的运行安全。

核酸检测的重排算法及其数值模拟

2022年春季上海遭受到奥密克戎变异株的侵袭,核酸检测是筛查新冠阳性病例的重要手段之一。目前社区常用核酸检测方式是10人/20人混合检测,重点人群单人单管复测。考虑到检测数量的庞大,二次复核易对非阳性人员造成恐慌,仿照CT成像原理,设计一种核酸检测重排方法,每人检测后将检测液分别随机置于多组不同试管中,根据不同组试管中的检测结果(投影数据),利用反投影方法,确定进入二次检测人员。计算机仿真结果表明,上述所设计的重排算法能够实现减少总检测数量和提高进入二次检测人员精度的目的。因此以上重排方法有望进一步应用到智能化的核酸采样机器人上,达到高效检测的目的。

融入PBL-IECT理念的大数据类专业课程重构研究

由于大数据类专业课程建设历程较短,实践教学案例少、可借鉴的教学经验不足等原因,课程教学仍然采用以传统理论讲授为主、上机实践为辅的教学模式。传统教学在知识更新、与行业实际接轨等方面很难取得令人满意的教学效果。通过对大数据类专业课程知识跨度大、内容更新快、实践性要求高、技术性强等特征进行分析,提出融入“PBL-IECT(项目驱动-专家协同)”理念的教学模式对大数据类专业课程进行重构,设计出以“项目驱动(PBL)”优化课程内容、以“专家协同(IECT)”优化教学模式的课程框架,以“数据采集与清洗”课程为例经过多轮教学实验发现,该模式对于激发学生的开创力、提升学生解决实际问题的能力效果明显。