Three-dimensional(3D)parametric measurements of individual gravels in the Gobi region using point cloud technique

Gobi spans a large area of China,surpassing the combined expanse of mobile dunes and semi-fixed dunes.Its presence significantly influences the movement of sand and dust.However,the complex origins and diverse materials constituting the Gobi result in notable differences in saltation processes across various Gobi surfaces.It is challenging to describe these processes according to a uniform morphology.Therefore,it becomes imperative to articulate surface characteristics through parameters such as the three-dimensional(3D)size and shape of gravel.Collecting morphology information for Gobi gravels is essential for studying its genesis and sand saltation.To enhance the efficiency and information yield of gravel parameter measurements,this study conducted field experiments in the Gobi region across Dunhuang City,Guazhou County,and Yumen City(administrated by Jiuquan City),Gansu Province,China in March 2023.A research framework and methodology for measuring 3D parameters of gravel using point cloud were developed,alongside improved calculation formulas for 3D parameters including gravel grain size,volume,flatness,roundness,sphericity,and equivalent grain size.Leveraging multi-view geometry technology for 3D reconstruction allowed for establishing an optimal data acquisition scheme characterized by high point cloud reconstruction efficiency and clear quality.Additionally,the proposed methodology incorporated point cloud clustering,segmentation,and filtering techniques to isolate individual gravel point clouds.Advanced point cloud algorithms,including the Oriented Bounding Box(OBB),point cloud slicing method,and point cloud triangulation,were then deployed to calculate the 3D parameters of individual gravels.These systematic processes allow precise and detailed characterization of individual gravels.For gravel grain size and volume,the correlation coefficients between point cloud and manual measurements all exceeded 0.9000,confirming the feasibility of the proposed methodology for measuring 3D parameters of individual gravels.The proposed workflow yields accurate calculations of relevant parameters for Gobi gravels,providing essential data support for subsequent studies on Gobi environments.

3D Echocardiogram Reconstruction Employing a Flip Directional Texture Pyramid

Three dimensional(3D)echocardiogram enables cardiologists to visua-lize suspicious cardiac structures in detail.In recent years,this three-dimensional echocardiogram carries important clinical value in virtual surgical simulation.However,this 3D echocardiogram involves a trade-off difficulty between accu-racy and efficient computation in clinical diagnosis.This paper presents a novel Flip Directional 3D Volume Reconstruction(FD-3DVR)method for the recon-struction of echocardiogram images.The proposed method consists of two main steps:multiplanar volumetric imaging and 3D volume reconstruction.In the crea-tion of multiplanar volumetric imaging,two-dimensional(2D)image pixels are mapped into voxels of the volumetric grid.As the obtained slices are discontin-uous,there are some missing voxels in the volume data.To restore the structural and textural information of 3D ultrasound volume,the proposed method creates a volume pyramid in parallel with theflip directional texture pyramid.Initially,the nearest neighbors of missing voxels in the multiplanar volumetric imaging are identified by 3D ANN(Approximate Nearest Neighbor)patch matching method.Furthermore,aflip directional texture pyramid is proposed and aggregated with distance in patch matching tofind out the most similar neighbors.In the recon-struction step,structural and textural information obtained from differentflip angle directions can reconstruct 3D volume well with the desired accuracy.Com-pared with existing 3D reconstruction methods,the proposed Flip Directional 3D Volume Reconstruction(FD-3DVR)method provides superior performance for the mean peak signal-to-noise ratio(40.538 for the proposed method I and 39.626 for the proposed method II).Experimental results performed on the cardi-ac datasets demonstrate the efficiency of the proposed method for the reconstruc-tion of echocardiogram images.

Three-Dimensional Model Reconstruction of Nonwovens from Multi-Focus Images

The three-dimensional(3D)model is of great significance to analyze the performance of nonwovens.However,the existing modelling methods could not reconstruct the 3D structure of nonwovens at low cost.A new method based on deep learning was proposed to reconstruct 3D models of nonwovens from multi-focus images.A convolutional neural network was trained to extract clear fibers from sequence images.Image processing algorithms were used to obtain the radius,the central axis,and depth information of fibers from the extraction results.Based on this information,3D models were built in 3D space.Furthermore,self-developed algorithms optimized the central axis and depth of fibers,which made fibers more realistic and continuous.The method with lower cost could reconstruct 3D models of nonwovens conveniently.

3D reconstruction method and connectivity rules of fracture networks generated under different mining layouts

In current research,a series of triaxial tests,which were employed to simulate three typical mining layouts(i.e.,top-coal caving,non-pillar mining and protected coal seam mining),were conducted on coal by using MTS815 Flex Test GT rock mechanics test system,and the fracture networks in the broken coal samples were qualitatively and quantitatively investigated by employing CT scanning and 3D reconstruction techniques.This work aimed at providing a detail description on the micro-structure and fractureconnectivity characteristics of rupture coal samples under different mining layouts.The results show that:(i)for protected coal seam mining layout,the coal specimens failure is in a compression-shear manner and oppositely,(ii)the tension-shear failure phenomenon is observed for top-coal caving and non-pillar mining layouts.By investigating the connectivity features of the generated fractures in the direction ofσ_1,under different mining layouts,it is found that the connectivity level of the fractures of the samples corresponding to non-pillar mining layout was the highest.

Vertebrae CT Images 3D Reconstruction with Improve Marching Cubes Algorithm

Medical images 3D reconstruction is an important part in medical image analysis and processing. Although lots of algorithms have been proposed continuously, speed and accuracy cannot conform to actual needs, which has always been the focus topic. In this paper, we propose an Improved Marching Cubes algorithm ( I-MC) based on the surface rendering theory, which implements 3D reconstruction of the vertebrae. Firstly, we preprocessed the original 2D vertebrae CT images with the bilateral-filter denoising algorithm. Secondly, on the basis of the traditional Marching Cubes algorithm, the seed voxels were extracted and the Region Growing algorithm was used to determine all voxels that contain isosurfaces. Then, the Golden Section instead of the traditional linear interpolation was used to calculate the equivalent point, and this method reduced the calculations of public edges. VTK and OpenGL implemented 3D reconstruction of the vertebrae on GPU quickly and accurately. The experimental results show that when compared with the traditional Marching Cubes algorithm and Mesh Simplification Marching Cubes algorithm, the improved algorithm achieves a significant improvement of reconstruction speed while preserving the accurate results. The efficiency of algorithm is improved dramatically. This method is real-time and achieves the goal of efficient 3D reconstruction of vertebrae CT images.

3D Vector Reconstruction of the Typical Cervical Vertebra from Anatomical Sections of Korean Visible Human at the Laboratory of Clinical and Digital Anatomy of Paris Descartes University

Aim: To carry out a 3D vector reconstruction of the typical cervical vertebra from anatomical sections of the “Korean Visible Human” for educational purposes. Material and Methods: The anatomical subject was a 33-year-old Korean man who died of leukemia. He was 164 cm tall and weighed 55 kg. This man donated his body to science. Her body was frozen and cut into several anatomical sections after an MRI and CT scan. These anatomical sections were made using a special saw called a 0.2 mm thick cryomacrotome. Thus 8100 cuts were obtained. Only the sections numbered 940 to 1200 were used for our study. A segmentation by manual contouring of the different parts of the typical cervical vertebra was made using the software Winsurf version 3.5 on a laptop PC running Windows 7 equipped with a Ram of 8 gigas. Results: Our 3D vector model of the typical cervical vertebra is easily manipulated using the Acrobat 3DPDF interface. Each part of the vertebra accessible in a menu can be displayed, hidden or made transparent, and 3D labels are available as well as educational menus for learning anatomy. Conclusion: This original work constitutes a remarkable educational tool for the anatomical study of the typical cervical vertebra and can also be used as a 3D atlas for simulation purposes for training in therapeutic gestures.

PC-BASED SURFACE RECONSTRUCTION OF MEDICAL CT IMAGES

It is an active research area to reconstruct 3-D object and display its visible surfacesfrom cross-sectional images. In this paper, the methods of reconstructing 3-D object from medicalCT images and displaying the visible surfaces are discussed. A polygon approximation methodthat forms polygon with the same number of segment points and a fast interpolation method forcross-sectional contours are presented at first. Then the voxel set of a human liver is reconstructed.And then the liver voxel set is displayed using depth and gradient shading methods. The softwareis written in C programming language at a microcomputer image processing system with a PC/ATcomputer as the host and a PC-VISION board as the image processing unit. The result of theprocessing is satisfying.

CT三维重建配合3D打印技术在辅助寰枢椎椎弓根螺钉置入的应用价值评估

目的:探讨CT三维重建配合3D打印技术在辅助寰枢椎椎弓根螺钉置入的应用价值。方法:通过CT三维重建的多种后处理技术明确寰枢椎病变13例作为观察组,再将CT三维重建、逆向工程原理及快速成形技术相结合,设计出一种新型的导航模板,辅助椎弓根螺钉置入,并与13例之前已通过X线透视置钉法的病例(对照组)进行置钉效果比较。结果:对照组13例共置椎弓根螺钉41枚,其中Ⅰ类置钉9枚,Ⅱ类置钉18枚,Ⅲ类置钉14枚,成功率65.9%;观察组共打印颈椎模型13例,设计导向模板21个,5例由于先前通过X线透视仅在枢椎两侧的椎弓根内置钉,只制作出枢椎的导航模板;模拟手术同样置钉41枚,其中Ⅰ类置钉15枚,Ⅱ类置钉21枚,Ⅲ类置钉5枚,成功率87.8%。结论:CT三维重建的各种后处理技术不仅能够准确的判断寰枢椎病变,并能配合3D打印技术,制作出个体化的导航模板,使上颈椎椎弓根螺钉的置入变得既安全又省时,并能在术后准确评估置钉效果。

口腔MSCT-3D与COPT对比研究

目的:通过与COPT对比,探究口腔MSCT-3D在临床中应用价值。材料和方法:COPT及MSCT各117例,COPT经计算机后处理,MSCT经工作站三维重建,根据影像结果,按金属牙、缺如和半残等项分别统计分析COPT及MSCT检查情况,并对摄影方法及影像后处理、摄影条件及照射剂量等项进行比较。结果:COPT牙齿正常9人(0.24%),正常记数3160颗(84.4%),异常记数551颗(15.6%),MSCT-3D牙齿正常11人(0.29%),正常记数3138颗(83.8%),异常记数606颗(16.2%)。摄影方式,COPT属曲面摄影,MSCT属断面螺旋摄影;影像后处理,COPT侧重2D曲面,2D效果优于MSCT,MSCT侧重3D立体,可行多种三维重建,3D效果优于COPT。照射剂量,MSCT远高于COPT。结论:口腔COPT2D影像性征显著;MSCT-3D在2D基础上,3D效果增加,但口腔专用,辐射剂量相对过大。

Characterization of 3D pore nanostructure and stress-dependent permeability of organic-rich shales in northern Guizhou Depression,China

The three-dimensional(3D)pore structures and permeability of shale are critical for forecasting gas production capacity and guiding pressure differential control in practical reservoir extraction.However,few investigations have analyzed the effects of microscopic organic matter(OM)morphology and 3D pore nanostructures on the stress sensitivity,which are precisely the most unique and controlling factors of reservoir quality in shales.In this study,ultra-high nanoscale-resolution imaging experiments,i.e.focused ion beam-scanning electron microscopy(FIB-SEMs),were conducted on two organic-rich shale samples from Longmaxi and Wufeng Formations in northern Guizhou Depression,China.Pore morphology,porosity of 3D pore nanostructures,pore size distribution,and connectivity of the six selected regions of interest(including clump-shaped OMs,interstitial OMs,framboidal pyrite,and microfractures)were qualitatively and quantitatively characterized.Pulse decay permeability(PDP)measurement was used to investigate the variation patterns of stress-dependent permeability and stress sensitivity of shales under different confining pressures and pore pressures,and the results were then used to calculate the Biot coefficients for the two shale formations.The results showed that the samples have high OM porosity and 85%of the OM pores have the radius of less than 40 nm.The OM morphology and pore structure characteristics of the Longmaxi and Wufeng Formations were distinctly different.In particular,the OM in the Wufeng Formation samples developed some OM pores with radius larger than500 nm,which significantly improved the connectivity.The macroscopic permeability strongly depends on the permeability of OM pores.The stress sensitivity of permeability of Wufeng Formation was significantly lower than that of Longmaxi Formation,due to the differences in OM morphology and pore structures.The Biot coefficients of 0.729 and 0.697 were obtained for the Longmaxi and Wufeng Formations,respectively.

混凝土CT图像的3维重建技术

为了建立更加真实的3维混凝土细观模型,进行破损机理的分析。利用3维图像处理软件MIMICS对原始的CT图像进行预处理,实现了混凝土真实细观结构的3维重建,将重建结果导入到大型商业有限元软件ANSYS中,建立了更加能准确表征混凝土细观非均质性的3维有限元数值模型。在此基础上,对重建的细观有限元模型进行了数值模拟,并与其它有限元模型的分析结果进行了比较。结果表明:所建立的3维混凝土细观模型可以弥补传统随机混凝土骨料模型的不足,较好地反映出混凝土材料内部的力学特性,为最终能够深入研究混凝土材料的细观破损机理开辟新的途径。

CT扫描技术在页岩油气储层微观结构表征中的应用进展

重点论述了CT扫描技术在岩石矿物组分、孔隙结构表征和微裂缝识别三个方面的应用进展。利用不同矿物组分的密度差异可以识别出有机质、黄铁矿和基质矿物等组分,由于一些矿物组分灰度值相近难以精确区分,未来可结合X衍射技术对比识别。实现了岩心内部真实孔喉分布的三维表征,并可进行定性定量的连通性分析。不仅可以识别页岩中发育的天然微裂缝,还可研究不同热解条件下的微裂缝扩展规律。CT扫描已然成为表征页岩油气储层微观结构的有力工具。

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

螺旋CT三维成像在颈椎损伤病变中的应用

目的 探讨螺旋CT三维成像 (MPR、SSD)在颈椎损伤中的应用价值。材料与方法 经X线和 /或螺旋CT证实的颈椎损伤 15例 ,行螺旋CT扫描 ,并作MPR和SSD成像 ,13例扫描参数为层厚 3mm ,床速 4.5mm/s ,重建间距 1.5mm ;2例为层厚 5mm ,床速5mm/s ,重建间距 2mm。SSD最低阈值选择 15 0～ 180。结果 椎体及附件骨折 10例 ,其中 6例伴环齿关节脱位 ,1例椎体滑脱。椎体旋转脱位 4例 ,成角滑脱 1例。 15例中 3例椎管狭窄并硬脊膜受压。MPR结合轴位图像可完全明确骨折、脱位及椎管情况。SSD对颈椎表面骨折、椎体旋转及成角脱位显示良好 ,立体感强 ,但对椎体内骨裂或骨折、椎管内病变显示差。结论 颈椎损伤应首选CT检查。轴位图像、MPR及SSD联合应用 ,能明确病变性质 ,立体、直观、多方位提供临床医师所需信息 ,有利于治疗方案的选择。

基于CT图像的混凝土三维微观结构在ANSYS中的实现

基于混凝土的CT平面图像信息,用APDL语言生成的程序对混凝土的三维微观结构在大型商业有限元软件ANSYS中进行三维重建。重建过程没有生成点、线、面、体等几何元素,而是利用CT平面图像信息直接生成节点,连接节点生成单元,避免了网格无法剖分现象的出现。生成的单元形状规则,长宽比合理。通过建立的更接近实际混凝土微观结构的数值模型,可利用有限元方法进一步研究基于微观结构的混凝土各项力学特性。

螺旋CT三维重建在磨牙区种植牙手术中的临床应用价值

采用ProspeedⅡ型螺旋CT对25例种植牙患者行术前扫描,将获得的数据信息进行多平面图像重建及术前分析设计,术后再次扫描和图像重建,分析种植术后效果;所有病例重建图均能清晰显示颌骨形态、质地和重要解剖结构,如颏孔、上颌窦、下牙槽神经管,并能精确的测量缺牙区可用骨的高度、厚度和宽度;利用CT技术辅助临床种植牙手术及术后评估有重要的临床意义。

多层螺旋CT血管成像在颈内动脉起始部狭窄介入治疗中的应用价值

目的探讨多层螺旋CT血管成像(MSCTA)在颈内动脉起始部狭窄的血管内介入治疗的应用。方法回顾性分析42例颈内动脉起始部狭窄行血管内介入诊疗的MSCTA影像资料,总结这些资料在该病治疗中的应用价值。结果MSCTA检查均能获得明确诊断。通过多平面重建测量42例84侧颈内动脉起始部的面积狭窄百分率,其中面积狭窄百分比≤50%者15支,狭窄程度在50%～70%者17支,>70%者30支,闭塞者4支,单侧正常者18例。MSCT重建技术能显示斑块及狭窄管腔内部形态。结论MSCTA可直观地显示颈内动脉起始部狭窄程度及斑块性质,在颈内动脉起始部支架内再狭窄的评价中起着重要作用。

耻骨支应力性骨折的螺旋CT表现

目的 提高对临床易忽略的耻骨支应力性骨折的认识 ,探讨其螺旋CT及三维重建的诊断价值。材料与方法 分析 2 6例耻骨支应力性骨折的螺旋CT及三维重建表现 ,并与X线平片对比。结果 螺旋CT轴位扫描对骨折线、骨痂、骨髓腔及周围软组织等细节显示清晰 ,SSD直观地显示了复杂的解剖结构及骨折的立体形态 ,斜位MPR有助于观察骨折的对位对线 ,MIP的优势并不明显 ,CT全部诊断正确 ,CT并发现骨痂旁气体生成及一侧耻骨下支双骨折各 1例。结论 螺旋CT及其三维重建对耻骨支应力性骨折的诊断及鉴别诊断有极高价值 。

Willis环解剖变异的64层容积CT数字减影血管造影研究

目的通过64层容积CT数字减影血管造影(volume CT digital subtraction angiography,VCTDSA)研究Willis环的正常解剖和变异。方法分析2006年2月至2008年9月在我院行头部或头颈部VCTDSA检查的174例患者资料,观测Willis环各组成动脉的发育情况、形态、大小,Willis环的完整性及Willis环穿支小血管的显示情况。结果①Willis环动脉发育不良各段均有发生,按发生率不同依次为L-PCoA(20.1%)、R-PCoA(16.1%)、R-ACA A1(13.8%)、R-PCA P1(9.2%)、ACoA(7.3%)、L-PCA P1(6.3%)及L-ACA A1(3.4%),动脉缺如以R-PCoA(54.6%)、L-PCoA(52.3%)、ACoA(15.8%)为高。②174个Willis环中,后循环发育不良或缺如占55.8%,前后循环发育不良或缺如占29.8%,具有完整形态Willis环的仅占9.2%。③174个Willis环清楚显示穿支血管17支,平均直径0.82 mm。Heubner回返动脉26支,平均直径0.94 mm。结论VCTDSA对Willis环显示完整、清晰,多角度显示能发现Willis环的各种变异,并显示Willis环穿支小血管。

应用螺旋CT三维重建颌面部软组织的研究

目的:评价螺旋CT在颌面部软组织重建中的价值。方法:对1例右耳缺损患者的头部进行螺旋CT扫描,扫描数据以DICOM格式储存。在诊断工作站上以SSD法对图像进行重建。结果:螺旋CT能一次快速精确完成整个头部的扫描与重建,面部软组织、器官重建图像清晰,但瞳孔位置不能显示。结论:对于头面部除瞳孔以外的软组织三维重建,可选择螺旋CT三维重建方式。