Local computed tomography via iterative deblurring

X-ray computed tomography is a major imaging modality. An iterative deblurring method is adapted for local reconstruction in parallel-beam and cone-beam geometries, utilizing only x-rays passing through a region of interest. The feasibility is demonstrated in numerical simulation with noise-free and noisy projection data. The iterative deblurring method has the theoretical advantages of maintaining nonnegativity, converging monotonically and minimizing Csiszàr's I-divergence.     

面向挤出中聚合物形态的层析图像处理方法的研究

依据光学信息论中的多维随机变量的联合熵、条件熵、平均互信息之间关系和互信息的链式法则,提出了面向挤出中聚合物形态的层析图像处理方法.它包括层析图像中的背景与分离、目标标度变换、亚像素插补的图像预处理和多模式目标特征图像的提取和测量.实验表明,通过该方法不仅能将目标形态从目标与背景之比为1∶9的层析图像中分辨出来,而且能提高目标图像的空间分辨率30%,解决了由于目标图像信息量小、对比度差而使得层析图像测量方法难以在工程中应用的问题.     

Error analysis on a generalized Feldkamp's cone-beam computed tomography algorithm

To overcome the limitations of Feldkamp's cone-beam reconstruction algorithm, we generalized it in the case of noncircular and nonplanar scanning. In this paper, an error analysis is performed on this generalized approximate algorithm. The study is based on a reconstruction error formula. Roughly speaking, the error is proportional to the distance from a voxel to the mid-plane in the planar scanning mode, to the pitch of a scanning locus in the helix-like scanning mode, and inversely proportional to the horizontal size of the scanning locus. The error also depends on longitudinal variation of a specimen function. Longitudinal partial derivative distributions of specimen transverse sections are modeled as stochastic fields. Practical factors are simulated as noise terms in the reconstruction error formula. The simulation results show that the generalized Feldkamp's algorithm is not sensitive to noise and allows more accurate reconstruction in the helix-like scanning mode.     

Effects of off-focal radiation on dimensional measurements in industrial cone-beam micro-focus X-ray computed tomography systems

A study of the secondary source phenomenon due to the presence of off-focal radiation in industrial micro-focus cone-beam X-ray computed tomography (XCT) systems and its influence on dimensional measurements is presented. Although off-focal radiation production within X-ray tubes has been studied for medical X-ray imaging systems, its properties and its effects on dimensional measurements in industrial XCT systems have not been discussed prior to this research. The study comprises: evaluation of the geometrical properties of off-focal radiation through a theoretical and experimental study of two-dimensional projection images of the scanned objects, verification of these properties using computer simulations and evaluation of the impact of the secondary source on dimensional measurements using experimental and simulation approaches. In addition, ways to minimise the effects of off-focal radiation are discussed, and reference samples for characterising the properties of off-focal radiation are proposed.     

Digital denture manufacturing-An integrated technologies of abrasive computer tomography, CNC machining and rapid prototyping

The orthodontic denture produced by the traditional method is heavily relied on the skill and experience of the technician. Its quality is depended on the accuracy of the technician’s subjective judgment. In addition, the manual process involves many steps that require a long time to complete. Most importantly, it does not preserve any quantitative information for future retrieval.In this paper, a novel device for scanning denture image and reconstructing 3D digital information of teeth models by abrasive computer tomography (ACT) is presented. The orthodontic denture is then to be produced by rapid prototyping (RP) or computer numerical control (CNC) machining methods based on the digital information. A force feedback sculptor (Freeform system, U.S.A.), using 3D touch technology, was applied to modify the teeth profile or features of the denture. It enables the dentist to perform digital manipulation of the denture profile with real-time and interactive operation. Due to its user-friendly human-computer interface, the dentist can directly access the 3-D model without relying on a CAD/CAM technician or denture technician. In this paper, the comparison between traditional manual operation and digital manufacture using RP and CNC machining technology for denture production is summarized.In this paper, a digital denture manufacturing protocol using an economic and harmless computer abrasive teeth profile scanning, computer-aided denture design, 3D touchable feature modification, and numerical denture manufacturing were proposed here. These proposed methods provide solid evidence that digital design and manufacturing technologies may become a new avenue for custom made denture design, analysis, and production in the 21th century.     

基于工业计算机断层成像技术的三维CAD模型重构方法

为解决复杂形状产品的三维计算机辅助设计模型的重构难题,提出了一种基于工业计算机断层成像技术的三维计算机辅助设计模型的重构方法.首先用工业计算机断层成像技术对产品进行扫描,得到产品切片图像,然后通过切片图像获取体数据;在采用高斯滤波对体数据进行预处理后,使用移动立方体算法重建三维表面,并用顶点删除法和二次误差测度算法简化三维表面;在采用Laplacian算法平滑三维表面后,将三维表面模型保存为STL格式的文件;最后,将STL格式的文件导入到UG中,重构出产品的三维计算机辅助设计模型.实际应用验证了该方法的有效性和正确性.     

Ossa cordis and os aorta in the one-humped camel: Computed tomography,light microscopy and morphometric analysis

The present study describes the morphological characteristics of the camel heart Ossa cordis, and os aorta using computed tomography soft tissue window (CT) alongside 3D render volume reconstructions and light microscopy. The current study techniques demonstrated the Ossa cordis and os aorta in the cardiac window with more precision than the black and white (ghost), and angiography images. Transverse and sagittal CT images additionally demonstrated the presence of Ossa cordis and os aorta. This study is the first to record two small Ossa cordis sinistrum and one os aorta in the camel heart, in addition to the more commonly observed singular, large, os cordis dextrum. The os cordis dextrum was always located in the upper part of the interventricular septum, near to its junction with the atrium, forming an elongated rectangular shape when observed transversally. The wider cranial part was composed from bone, whereas the caudal aspect was narrow and contained both bone and cartilage. Light microscopy identified that the os cordis dextrum consisted of trabecular bone, marrow spaces, and hyaline cartilage. Two Ossa cordis sinistrum were detected on the left side of the heart, one in the right fibrous ring and another in the interventricular septum, microscopy showed that both contained only trabecular bone with osteocytes, osteoblasts, and osteoclasts. At the level of ascending aorta, there was also trabecular bone containing osteocytes, an os aorta.     

Hydrodynamics analysis in micro-channels of a viscous coupling using gamma-ray computed tomography

In this work, high-resolution gamma-ray computed tomography (HireCT) was applied for the first time on a viscous coupling to visualize the internal working fluid distribution. The HireCT measurement system comprises a ¹³⁷Cs isotopic source and a gamma-ray detector arc operated in single photon counting mode. It is able to produce cross-sectional images of dense objects with a spatial resolution of about 2 mm. To scan fast rotating parts time-averaged rotation-synchronized CT scanning mode was employed in these experiments. The analyzed viscous coupling (Visco^® clutch of MAHLE Behr) mainly consists of a driven primary disc and a secondary housing with an engine cooling fan mounted on it. The viscous coupling is assembled within an experimental rig. Its primary and secondary parts are axially assembled and a working liquid is pumped into engaged radial ring profiles to provide a defined torque transfer. The internal ring channel width, where the working liquid is to be observed, is considerably lower than one millimeter. Although the HireCT measurement system is not able to resolve these micro-channels, the working liquid can be successfully visualized via its phase contrast. Investigations have been performed at different filling levels corresponding to different transmission slips of the test viscous coupling. Moreover, both radial and tangential liquid distributions for different operational steady states could be determined. Finally, the obtained experimental data were compared to results from computational fluid dynamics (CFD) simulations in some operating points and were in good agreement.     

Sensitivity of X-ray computed tomography measurements of a gas-solid flow to variations in acquisition parameters

Due to its high spatial resolution and non-invasive nature, X-ray computed tomography has become a popular method for determining the flow characteristics of multiphase flows. However, because many of the X-ray computed tomography systems used for non-destructive imaging of multiphase flows provide the operator wide leeway in the selection of imaging parameters, the potential exists for errors to be introduced into the measurements if the algorithms are sensitive to these changes. In this paper, a representative multiphase flow (specifically, a fluidized bed) is imaged with a wide range of X-ray tube electrical potentials, currents, and detector exposure times and reconstructed with a wide range of centers of rotation. The results of these tests show that while the raw CT intensities are sensitive to these parameter variations, once the measurements are calibrated to reference images (in this case through a void fraction calculation), the final results are insensitive to most changes. In the extreme cases where there is some sensitivity to the parameter changes, the causes and practical implications are discussed.     

A cone‐beam computed tomography study of the anatomical relationships between mandibular teeth and the mandibular canal,with a review of the current literature

The purpose of this study was to evaluate age‐ and sex‐related changes in the anatomical relationships between the roots of the molars and premolars and the mandibular canal using cone‐beam computed tomography (CBCT) images. A total of 243 patients (116 males, 127 females) aged 16–83 years for whom previous CBCT scans were available were enrolled in this study. The patients were subcategorized by sex and age (Group I, <21 years; Group II, 21–40 years; and Group III, >40 years). The distances between the mandibular canal and the molars and premolars were measured. The mandibular canal was significantly closer to the root apices of the second and third molars than to the apices of other evaluated teeth (p < 0.05). All measurements were significantly higher in male than in female subjects (p < 0.05). Group I subjects exhibited significantly shorter distances between the mandibular canal and root apices of the first and second premolars, and the molars, than those of Group II and III subjects (p < 0.05). Direct contact relationships were found in 1.6%, 3.3%, 3.3%, 16%, and 32.2% of teeth (running from the first premolar to the third molar, respectively). Age and sex influenced the anatomical relationships between mandibular teeth and the mandibular canal, and these should be considered when planning endodontic and surgical procedures to avoid potential nerve injury.     

基于神经网络边缘提取的工业断层成像图像拟合

通过工业计算机断层成像图像边缘拟合,可获得矢量化的曲线,进而获得工件的计算机辅助设计图纸,实现基于工业断层成像的机械零部件逆向设计。在用两组细胞神经网络对图像进行分割的基础上,进行边缘跟踪和曲线的多维拟合。通过横截圆和轴线的拟合,实现对圆柱形目标的拟合。轴线拟合时,将各层圆心坐标分别投影到xz平面和yz平面进行最小二乘拟合,以降低计算复杂度。对发动机切片图像进行实验,根据拟合得到的参数得出了圆柱形目标的计算机辅助设计图,其拟合均方误差小于0.3像素2。对不规则目标,讨论了基于最小二乘法的分段三次曲线拟合方法在边缘曲线拟合中的应用;对发动机切片图像目标区域进行实验的拟合均方误差均小于0.6像素2。实验结果和误差分析证明,文中的拟合方法是有效的,实现了基于工业断层成像的逆向设计所必需的位图矢量化。     

Application of gamma-ray computed tomography for the analysis of gas holdup distributions in centrifugal pumps

In this work, gas–liquid distributions in an industrial centrifugal pump operated at various steady state conditions have been quantitatively determined. Therefore, high-resolution gamma-ray computed tomography (HireCT) has been applied, operated in time-averaging rotation-synchronized CT scanning mode. Detailed studies have been performed on a hydraulic test facility providing authentic operating conditions for industrial centrifugal pumps. The gas phase distribution in the centrifugal pump has been studied for swirling gas–liquid two-phase flow as an inlet flow regime and at defined inlet gas volumetric flow rates between 0% and 5%. In this way, the influence of the inlet flow boundary conditions on the performance of the centrifugal pump as well as the gas holdup distribution within the impeller region could be successfully determined.     

Lungs nodule detection framework from computed tomography images using support vector machine

The emergence of cloud infrastructure has the potential to provide significant benefits in a variety of areas in the medical imaging field. The driving force behind the extensive use of cloud infrastructure for medical image processing is the exponential increase in the size of computed tomography (CT) and magnetic resonance imaging (MRI) data. The size of a single CT/MRI image has increased manifold since the inception of these imagery techniques. This demand for the introduction of effective and efficient frameworks for extracting relevant and most suitable information (features) from these sizeable images. As early detection of lungs cancer can significantly increase the chances of survival of a lung scanner patient, an effective and efficient nodule detection system can play a vital role. In this article, we have proposed a novel classification framework for lungs nodule classification with less false positive rates (FPRs), high accuracy, sensitivity rate, less computationally expensive and uses a small set of features while preserving edge and texture information. The proposed framework comprises multiple phases that include image contrast enhancement, segmentation, feature extraction, followed by an employment of these features for training and testing of a selected classifier. Image preprocessing and feature selection being the primary steps—playing their vital role in achieving improved classification accuracy. We have empirically tested the efficacy of our technique by utilizing the well‐known Lungs Image Consortium Database dataset. The results prove that the technique is highly effective for reducing FPRs with an impressive sensitivity rate of 97.45%.     

Evaluation of the standard measurement uncertainty due to the ISO50 surface determination method for dimensional computed tomography

Surface determination is the process by which a CT volume is converted from an image-based representation of an object to a surface-based representation. The process of surface determination relies on well-established image processing algorithms, but these algorithms are not exact, surface determination therefore contributes a component of uncertainty to X-ray CT based dimensional measurements. The purpose of this work is to develop a method for quantifying the standard uncertainty due to surface determination such that this standard uncertainty can be combined with other standard uncertainties in order to calculate the combined standard uncertainty for X-ray CT based dimensional measurements. The proposed method relies on evaluating the mode and the 68% dispersion of the air and material grey values of a given CT data-set. These values are propagated through the ISO50 threshold calculation to give the standard uncertainty of the ISO50 threshold value from which the standard uncertainty due to the ISO50 surface determination method can be evaluated. The proposed method is verified numerically and then demonstrated experimentally for dimensional measurements of an aluminium workpiece, a polymer workpiece, and a steel additively manufactured workpiece. The results show that the measurement uncertainty due to the ISO50 surface determination method is largest for dimensions that have both internal and external surfaces such as wall thicknesses, followed by dimensions such as internal and external diameters, whilst dimensions that are not sensitive to surface determination, for example centre-to-centre distances have the smallest uncertainty due to the ISO50 surface determination method.     

Cryostatic micro-computed tomography imaging of arterial wall perfusion

A double-walled copper vessel, 32 cc in volume, was fabricated for scanning tissue specimens while maintained below freezing point. To keep specimen temperature within +/- 1 degrees C, temperature sensors within the chamber control, the rate of inflow of the cold nitrogen gas vented through the chamber. The specimen is attached to a small platform on top of a vertical pin which is attached to the computer-controlled rotating stage under the vessel. The purpose of this arrangement is to permit scanning of specimens up to 2 cm3 that (1) cannot be "fixed" (e.g., with formalin) because of analyses which are incompatible with prior fixation (certain immunohistochemistry and biomolecular methods), or (2) are "snap"-frozen during a transient process, such as the accumulation and/or washout of radiopaque indicators. Examples of "cryoscans" of porcine carotid and coronary artery wall opacification in either untouched or acutely stented arteries, snap-frozen immediately after selective intra-arterial injection of a contrast agent, show accumulation of contrast in the extravascular space indicating increased endothelial permeability or endothelial and medial disruption following stent placement. The detection of contrast in the adventitia suggest that vasa vasorum deliver the contrast agent from the main lumen to the adventitial extravascular space but not to the media.     

Cryo-electron tomography: methodology, developments and biological applications

Cryo-electron tomography allows three-dimensional visualization of frozen-hydrated, vitrified biological material at molecular resolution. Here, we summarize the most important sample preparation methods and technical aspects relevant for cryo-electron tomography, as well as its recent biological applications from isolated macromolecular complexes to entire cells and tissues.     

Porosity measurements by X-ray computed tomography: Accuracy evaluation using a calibrated object

Accurate identification and measurement of internal voids and porosity is an important step towards improvement of production processes to obtain high quality materials and products. Recently, the importance of knowing the exact size, shape, volume and location of defects has become even higher as tighter requirements and new standards have been introduced in industry. There are several well-established methods for defects evaluation based on various principles (both destructive and non-destructive). However, all conventional methods have various deficiencies and the information about internal voids/porosity that can be extracted is limited. Most of these drawbacks can be overcome by using X-ray computed tomography (CT). Unlike other methods, CT provides full three-dimensional information about shape, size and distribution of internal voids and porosity; however, the accuracy of measurements is still under investigation. Hence, further evaluations on CT porosity measurements must be performed in order to consider X-ray computed tomography a reliable instrument for the assessment and detection of internal defects.A reference object with artificial defects was used in this research work in order to evaluate the accuracy of porosity measurements by CT. The reference object was manufactured by ultra-precision micro-milling. The object contains dismountable components with embedded internal hemispherical features that simulate internal porosity. The artificial porosity was micro-milled on top surfaces of dismountable cylindrical inserts. The hemispherical calottes were thereafter calibrated by traceable coordinate measuring systems and calibrated values were compared to actual values measured by a CT system. The accuracy of CT porosity measurements was then evaluated based on results obtained on various measurands, using different software tools and measuring procedures, comparing real scans to numerical simulations and investigating the influence of CT system parameters settings on measurement results.     

基于工业CT图像的数控代码直接生成方法研究

以曲面形状简单、可直接仿制的产品为对象,提出了由工业计算机断层成像技术图像直接生成数控代码的方法.该方法首先对产品的切片图像进行边缘提取与轮廓跟踪,再采用B样条曲线进行轮廓拟合,然后引入平面任意区域加工填充技术,逐层生成刀具路径并进行有序连接,最后生成数控代码.在B样条曲线拟合中,为了提高拟合精度,提出了一种基于特征点提取与线段类型识别的型值点选取法;在数控代码生成步骤中,改进了单层切片轮廓岛屿关系判别方法,提高了判别正确率.开发了软件系统,将该软件生成的数控代码输入到加工仿真软件中,仿真结果验证了数控代码生成方法的正确性.     

Conformance and nonconformance in segmentation-free X-ray computed tomography geometric inspection

Additive Manufacturing (AM) is changing the manufacturing paradigm as it makes it possible to generate complex geometries that are impossible using conventional technologies. However, conventional GPS/GD&T practices are inadequate both at specifying and verifying geometric tolerances. In both cases, they lack the required flexibility. Applying volumetric instead of surface representations helps to solve the problem of specifying tolerances and coheres with topological optimization. The verification paradigm must be modified, too, as AM allows an increase in part complexity without a corresponding increase of cost. Among measurement techniques, only X-ray computed tomography (XCT), which is volumetric, is capable of easily measure complex parts. Leaving the discussion of volumetric tolerance specifications to the future, the aim of this work is exploring a part geometric accuracy verification by direct comparison between its nominal geometry and geometric tolerance volumetric representation, and an XCT volumetric image of it. Unlike the conventional use of XCT for geometric verification, this is a segmentation-free verification. The method is based on the “mutual information” of the two, i.e. information shared by the measured and nominal representations. The output is a conformance statement that does rely on a measurement but nor on a specific measured value not rely on a measurement result. This makes defining a decision rule considering consumer's and producer's risks difficult: uncertainty does not exist in this case. Statistic and simulation techniques make it possible to estimate these risks, defining a numerical model of the distribution of the gray values in a specific portion of the XCT image. Finally, an additive manufacturing case study validates the methodology.