基于B样条插值的局部均值分解方法研究

局部均值分解(Local Mean Decomposition,LMD)方法是一种较新的自适应信号分析方法。LMD算法的核心思想是将原始信号分解为多个乘积函数(Production Function,PF),其中每个PF都是一个包络函数和一个纯调频函数的乘积。在LMD算法中需要提取信号的局部均值函数和包络估计,然而常规的提取方法会带来局部误差且分解速度慢。为了解决此问题,提出了利用三次B样条对信号上、下极值点进行插值得到上、下包络线,进而获取信号局部均值和包络估计的新方法。对仿真信号和机械振动信号的对比实验验证了该方法的优越性。     

NURBS curve interpolation algorithm based on tool radius compensation method

This paper focuses on developing an algorithm that can generate toolpaths in NURBS form for smooth, high speed and accurate machining. The initial toolpaths are obtained by tool radius compensation method which is based on the workpiece boundary offsetting. According to different lengths and the continuous short block (CSB) criterion, these offset linear segments can be regarded as CSBs or long straight segments. Junctions are located where the curvature value is greater than the preset curvature threshold value or where it changes abruptly, or at the two end points of any long straight segment. During machining, the NURBS fitting module first looks ahead several CSBs and converts them into parametric curves in real time. During the conversion, continuities of the position, slope or even curvature at the transition of the parametric curves and unfitted line segments can be guaranteed. Then the acceleration/deceleration feedrate-planning scheme is proposed to determine the transition feedrate at the junction between the fitted curves and unfitted long straight segments, and the corner feedrate within the fitted curve. Simulations and experiments show that the proposed algorithm can significantly improve machining accuracy and reduce cutting time to satisfy today’s high-speed and high-accurate machining requirements.     

Relation between computed tomography and diffraction tomography

The relationship between computed tomography (CAT) and diffraction tomography (DT) is investigated. A simple condition with a clear physical meaning is derived for the applicability of CAT. Corrections due to scattering are incorporated into CAT, and it is shown that the effect of scattering may be characterized by a two-dimensional fractional Fourier transform. The implications of these results for the three-dimensional imaging of weakly scattering objects are also discussed.     

Geometrical analysis of woven fabric microstructure based on micron-resolution computed tomography data

The global mechanical properties of textiles such as elasticity and strength, as well as transport properties such as permeability depend strongly on the microstructure of the textile. Textiles are heterogeneous structures with highly anisotropic material properties, including local fiber orientation and local fiber volume fraction. In this paper, an algorithm is presented to generate a virtual 3D–model of a woven fabric architecture with information about the local fiber orientation and the local fiber volume fraction. The geometric data of the woven fabric impregnated with resin was obtained by micron-resolution computed tomography (μCT). The volumetric μCT-scan was discretized into cells and the microstructure of each cell was analyzed and homogenized. Furthermore, the discretized data was used to calculate the local permeability tensors of each cell. An example application of the analyzed data is the simulation of the resin flow through a woven fabric based on the determined local permeability tensors and on Darcy’s law. The presented algorithm is an automated and robust method of going from μCT-scans to structural or flow models.     

Automatic annotation of liver computed tomography images based on a vessel-skeletonization method

Anatomical analysis of liver region is an essential and key step for liver-related disease diagnosis and treatment. One of the challenging issues is to annotate the functional regions of liver automatically or semi- automatically by analyzing Computed Tomography (CT) images. The present study developed a complete liver annotation system with an improved vessel-skeletonization method is proposed for CT images. In the first step, an automatic level set method and a customized region-growing method are applied to extract the liver region including vessels and tumors. Next, a modified iterative thinning method is developed to obtain the geometric structure of liver vessels and mark a vessel skeleton. The three-dimensional information is transformed into a tree data structure for storage. Based on the branch distribution of portal vein skeleton, a model-based method with a modified nearest neighbor segment approximation (NNSA) algorithm is adopted for the functional liver anatomy. Three experiments involving five 64-row liver CT datasets are performed. The accuracies of segmentation and annotation results were validated by an experienced doctor. Compared with different methods, our proposed vessel skeletonization method can simultaneously preserve the connectivity of the vasculature topology and generate the skeleton in a shorter time. Furthermore, our proposed annotation system can provide both visual and measurable information of livers. These experimental results demonstrate the usefulness and effectiveness of our proposed method. Our liver annotation system is helpful to evaluate the function of liver system and support diagnosis of liver disease.     

An X-ray computed tomography imaging agent based on long-circulating bismuth sulphide nanoparticles

Nanomaterials have become increasingly important in the development of new molecular probes for in vivo imaging, both experimentally and clinically. Nanoparticulate imaging probes have included semiconductor quantum dots, magnetic and magnetofluorescent nanoparticles, gold nanoparticles and nanoshells, among others. However, the use of nanomaterials for one of the most common imaging techniques, computed tomography (CT), has remained unexplored. Current CT contrast agents are based on small iodinated molecules. They are effective in absorbing X-rays, but non-specific distribution and rapid pharmacokinetics have rather limited their microvascular and targeting performance. Here we propose the use of a polymer-coated Bi(2)S(3) nanoparticle preparation as an injectable CT imaging agent. This preparation demonstrates excellent stability at high concentrations (0.25 M Bi(3+)), high X-ray absorption (fivefold better than iodine), very long circulation times (>2 h) in vivo and an efficacy/safety profile comparable to or better than iodinated imaging agents. We show the utility of these polymer-coated Bi(2)S(3) nanoparticles for enhanced in vivo imaging of the vasculature, the liver and lymph nodes in mice. These nanoparticles and their bioconjugates are expected to become an important adjunct to in vivo imaging of molecular targets and pathological conditions.     

基于X射线计算机断层扫描技术的重组竹湿热耦合老化评估

为了预测重组竹制品在实际使用中的寿命,基于X射线计算机断层扫描技术（X-ray computed tomography technology,X-CT）,采用标准BS EN 1087-1：1995作为重组竹湿热耦合老化条件,以其CT值和老化分析指标的数学模型评估重组竹湿热耦合老化后结构强度的损失。结果表明：重组竹老化后密度、内胶合强度和CT值均小于老化前,且老化前后差异显著。随老化时间增加,其密度、内胶合强度和CT值的损失均增加,且变化趋势基本一致,在1~2 h阶段变化较大,在2.5~4.5 h阶段变化较平缓,在老化4.5 h时达到峰值;将CT值差值与密度差值拟合为线性模型,模型相关系数R²=0.9270,验证模型R²=0.9438。CT值差值与内胶合强度差值拟合为Allometric模型,模型相关系数R²=0.9488,验证模型R²=0.9439;竹材自身的植物学特征及重组竹压制工艺造成了试验数据离散及老化前后离散程度发生改变。可通过改善重组竹制备工艺提高其内部均匀性及降低老化前后离散程度变化,以提高模型预测精度。     

A test device for damage characterisation of composites based on in situ computed tomography

For engineering design of composites, suitable damage models are required which have to predict the onset of damage, the successive failure and the subsequent reduction of the mechanical properties. To verify existing modelling approaches, the clear experimental identification of the particular damage entities is an essential condition. However, due to the complexity of the failure mechanisms of novel materials like heterogeneous textile composites, a comprehensive damage analysis is still a challenging problem. Recent progress in the field of computed tomography enables in situ measurements to detect damage phenomena in composites under loading. The article describes such a novel test device that combines an integrated testing machine with a high precision computer tomograph. The in situ method was used to study the damage evolution in carbon fibre reinforced plastics (CFRPs) made of weft knitted and woven preforms. A special focus was set to damage processes under loading in thickness direction. For this purpose, cylindrical tensile specimens according to ASTM D 7291 were manufactured and tested. Compression specimens with different aspect ratios have been used to study the compressive failure of CFRP woven composites. The experimental results are discussed with respect to the possibilities and limitations of the in situ based test method.     

Image inpainting algorithm based on partial differential equation technique

Abstract

Image inpainting is the process of filling in missing parts of damaged images based on information gleaned from surrounding areas. In this paper, we present two variational models for image inpainting. Combining two models, we can simultaneously fill in missing, corrupted or undesirable information, while remove noise. We explain that diffusion performance of the proposed models is essentially superior to that of TV inpainting model by analysing the physical characteristics in local coordinates, and investigate the existence of minimising functionals in BV space. The experimental results show the effective performance of the proposed models in restoring scratched photos, text removal, and even removal of entire objects from images.     

Computation of permeability of a non-crimp carbon textile reinforcement based on X-ray computed tomography images

The paper demonstrates the possibility of a correct (within the experimental scatter) calculation of a textile reinforcement permeability based on X-ray micro-computed tomography registration of the textile internal architecture, introduces the image segmentation procedures to achieve the necessary precision of reconstruction of the geometry and studies variability of the geometry and local permeability. The homogenized permeability of a non-crimp textile reinforcement is computed using computational fluid dynamics with voxel geometrical models. The models are constructed from X-ray computed tomography images using a statistical image segmentation method based on a Gaussian mixture model. The computed permeability shows a significant variability across different unit cells, in the range of (0.5…3.5) × 10⁻⁴ mm², which is strongly correlated with the solid volume fraction in the unit cell.     

Fuzzy relevance vector machine based classification of lung nodules in computed tomography images

Lung cancer is a critical disease with growing death rate, hence, the faster identification and treatment of lung cancer is essential. In medical image processing, the traditional methods like support vector machine, relevance vector machine for classifying cancer tissues are less sensitive to false data and required optimal improvement in classification accuracy. The proposed system of accurate lung cancer classification is obtained by a hybrid fuzzy relevance vector machine (FRVM) classifier with correlation negation ant colony optimization (CNACO) algorithm. This system provides enhanced accuracy and sensitivity by implementing two stages of feature extraction, image thresholding, and tumor segmentation, with a novel feature selection and tumor classification algorithm. The best features are selected by the proposed CNACO algorithm. The selected features are labeled and classified by FRVM classifier. The proposed classification scheme is validated on lung image database consortium and image database resource initiative public database and obtained accuracy of about 98.75%.     

Damage tolerant design of cast components based on defects detected by 3D X-ray computed tomography

This paper presents the application of 3D X-ray computed tomography (XCT) in deterministic fatigue strength analysis of relatively large cast components and also probabilistic fatigue design of heavy-section castings. To this end, more than 100 fatigue specimens were cut from a rejected wind turbine hub casting. XCT was used to find the 3D map of defects in selected fatigue specimens. All fatigue specimens were axially tested at R = −1 at room temperature and fatigue life scatter was established. Fractography analysis of broken specimens was performed. For CT scanned specimens, the defect sizes and positions obtained by XCT, in conjunction with the (nearly homogeneous) stress distribution of the specimens were used to predict the fatigue life and also the position of the fatigue crack initiation site. The predicted fatigue life and crack initiation position for CT scanned specimens were compared with experimental results. The obtained defect distribution by XCT was used in a random defect analysis to establish the scatter of fatigue life for the analyzed specimens. The predicted fatigue life scatter was compared with experimental results. The comparison showed that random defect analysis can successfully predict the scatter of fatigue life and may be used to find the probability of failure of cast components, based on the given defect distribution.     

A study on optimal scan conditions of Big Bore multi-slice computed tomography based on radiation dose and image noise

The newly introduced Big Bore computed tomography (CT) has a possibility to increase the tube current product scan time (mA s) for compensation of image degradation due to larger gentry opening without sound guideline. The objective of this paper is to derive optimal scan conditions for Big Bore CT scanner, mainly relating to the dose of diagnostic CT. The weighted CT dose index (CTDI(w)) was estimated at five typical protocols, such as head and neck, brain, paediatric, chest and abdomen. Noises were analysed in a circle of 1 or 2 cm of diameter in CT image slice. The results showed that measured CTDI(w) values generally follow the theoretical rule at all scanning conditions of every protocol. Although image noises decrease with increment of mA s, analysed image noises do follow the theoretical rule, but only in specific protocols. This phenomenon is presumed to result from the photon energy spectra arriving at the detection system of the Big Bore scanner.     

医用CT剂量指数测量结果的不确定度评定

为了使医用诊断计算机断层摄影装置（CT）X射线辐射源在模体中的剂量指数测量结果的不确定度评定合理。基于用带有100mm长杆电离室的积分剂量仪测量CT剂量指数的数学模型,对其测量不确定度来源进行分析,列出了方差、灵敏系数及标准不确定度的计算公式,从而给出了CT剂量指数测量的合成标准不确定度和扩展不确定度。     

Comparison of computed tomography dose reporting software

Computed tomography (CT) dose reporting software facilitates the estimation of doses to patients undergoing CT examinations. In this study, comparison of three software packages, i.e. CT-Expo (version 1.5, Medizinische Hochschule, Hannover, Germany), ImPACT CT Patients Dosimetry Calculator (version 0.99×, Imaging Performance Assessment on Computed Tomography, www.impactscan.org) and WinDose (version 2.1a, Wellhofer Dosimetry, Schwarzenbruck, Germany), has been made in terms of their calculation algorithm and the results of calculated doses. Estimations were performed for head, chest, abdominal and pelvic examinations based on the protocols recommended by European guidelines using single-slice CT (SSCT) (Siemens Somatom Plus 4, Erlangen, Germany) and multi-slice CT (MSCT) (Siemens Sensation 16, Erlangen, Germany) for software-based female and male phantoms. The results showed that there are some differences in final dose reporting provided by these software packages. There are deviations of effective doses produced by these software packages. Percentages of coefficient of variance range from 3.3 to 23.4 % in SSCT and from 10.6 to 43.8 % in MSCT. It is important that researchers state the name of the software that is used to estimate the various CT dose quantities. Users must also understand the equivalent terminologies between the information obtained from the CT console and the software packages in order to use the software correctly.     

Lamb波CT成像的实验研究

根据Ｘ射线ＣＴ成像原理和方法，利用Ｌａｍｂ波对薄层铝板的人工伤进行了ＣＴ成像的实验研究，得到较好的成像结果。     

Dual-reciprocity BEM based on global interpolation functions

Several global shape functions are introduced to interpolate the body-force term in the dual-reciprocity boundary-element method. These global-interpolation functions, which include polynomial, trigonometric, and hyperbolic series, can be used in place of the locally based radial shape function. For the several examples presented, the global functions have demonstrated superior convergence properties.     

利用二维插值核的高分辨力图像重构

利用连续图像采样及其内插公式,提出了一种基于二维插值核重建高分辨力图像的新算法。该算法先使一般低分辨力序列图像具有标准位移关系,再根据高、低分辨力图像之间的关系重构高分辨力图像。同时利用正则化技术导出了一套重复迭代算法,以提高算法的处理效果和克服病态问题。实验表明,该算法使图像的细节和清晰度大大增强,分辨力大幅度提高,明显优于零阶保持插值算法的处理结果,其峰值信噪比提高8-9dB。