Multiple Parameters Calibration for DOT Open System

Practical imaging system needs to be carefully calibrated before it is used for imaging algorithm design and verification. In this work, we have implemented a proof-of-principle FPGA controlled diffuse optical tomography (DOT) open system for our DOT and X-ray computed tomography (XCT) bi-modality joint reconstruction research, and calibrated parameters of this imaging system needed for DOT data acquisition and coordinate matching with XCT, including the conversion ratio of energy into gray level of the detector, the magnification of the lens, the distances between the scanner axes to the detector and the distances between the scanner axes and the phantom.     

An integrated measurement system for simultaneous functional magnetic resonance imaging and diffuse optical tomography in human brain mapping

An integrated measurement system is described for performing simultaneous functional magnetic resonance imaging (fMRI) and diffuse optical tomography (DOT) for human brain mapping experiments. The components of this system consist of an MRI-compatible multi-overlapping-channel optical probe, methods for co-registration of optical and fMRI measurements, and DOT reconstruction algorithms with structural and physiological constraints derived from the MRI data. The optical probe is fully MRI-compatible in the sense that it produces negligible MR image distortion and does not require any modification to the MRI scanner or data acquisition protocol. The probe can be attached to any part of the head without posing any limitation on optical data acquisition. Co-registration of images from fMRI and optical measurements was achieved by localizing the positions of the optical fibers using MRI markers. Human studies show successful implementation of the entire system.     

Areal surface texture data extraction from X-ray computed tomography reconstructions of metal additively manufactured parts

Many applications that exploit the manufacturing flexibility of additive manufacturing (AM) produce surfaces, primarily internal features, which cannot be measured using conventional contact or line-of-sight optical methods. This paper evaluates the capability of a novel technique to extract areal surface data from micro-focus X-ray computed tomography (XCT) from AM components and then generate surface parameter data per ISO 25178-2. This non-destructive evaluation of internal features has potential advantages during AM product research and commercial production. The data extracted from XCT is compared with data extracted using a focus variation instrument. A reference dimensional artefact is included in all XCT measurements to evaluate XCT surface determination performance and dimensional scaling accuracy. Selected areal parameters generated using the extraction technique are compared, including Sa, for which the nominal difference between the value obtained using XCT and used the focus variation method was less than 2.5%.     

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.     

Characterization of acoustically engineered polymer nanocomposite metamaterials using x-ray microcomputed tomography

We demonstrate the fabrication of acoustically engineered diamond nanoparticles-based metamaterials and their internal microstructure characterization using x-ray microcomputed tomography (XμCT). The state-of-the-art technique based on the radiation force of ultrasound standing (or stationary) waves in a rectangular chamber is utilized to pattern clusters of 5-nm-diameter diamond nanoparticles in parallel planes within a three-dimensional (3D) matrix of epoxy before solidification. Gradually, the periodic pattern becomes permanent with full cure of the epoxy matrix so as to form a 3D metamaterial structure. We also show that the periodicity of the pattern can be changed by selecting a different ultrasound frequency. Furthermore, XμCT is used as a quality control tool to map the internal structure and characterize each metamaterial. The ultimate application is to use the results as a base for the development of finite-element models which take into account all the structural features to study the various metamaterial (optical, acoustical, thermal, etc.) functional properties.     

Material influence in coordinate measurement using X-ray CT

The X-ray computed tomography system (XCT) as a coordinate measuring system has been increasingly introduced into the manufacturing industry because of its capability of measuring internal features. However, the metrological performance evaluation method for XCT has not yet been standardized. One of the biggest reasons of this is the difficulty in evaluating the material influence. The previous research by the authors revealed that the material influence significantly affects the form of the object to be measured. ISO/TC 213/WG 10, which covers the ISO standards of coordinate measuring machines, proposes the introduction of an additional object, called an “obstructive body,” by which the material influence is enhanced. This study presents the experimental results and a software simulation, in which the material influence is produced in a specific area and not on the entire surface of the test object. Additionally, requirements for the obstructive body in the industrial standardization of performance evaluation methods for XCT are proposed.     

X-ray excited optical luminescence detection by scanning near-field optical microscope: a new tool for nanoscience

Investigations of complex nanostructured materials used in modern technologies require special experimental techniques able to provide information on the structure and electronic properties of materials with a spatial resolution down to the nanometer scale. We tried to address these needs through the combination of x-ray absorption spectroscopy (XAS) using synchrotron radiation microbeams with scanning near-field optical microscopy (SNOM) detection of the x-ray excited optical luminescence (XEOL) signal. This new instrumentation offers the possibility to carry out a selective structural analysis of the sample surface with the subwavelength spatial resolution determined by the SNOM probe aperture. In addition, the apex of the optical fiber plays the role of a topographic probe, and chemical and topographic mappings can be simultaneously recorded. Our working XAS-SNOM prototype is based on a quartz tuning-fork head mounted on a high stability nanopositioning system; a coated optical fiber tip, operating as a probe in shear-force mode; a detection system coupled with the microscope head control system; and a dedicated software/hardware setup for synchronization of the XEOL signal detection with the synchrotron beamline acquisition system. We illustrate the possibility to obtain an element-specific contrast and to perform nano-XAS experiments by detecting the Zn K and W L(3) absorption edges in luminescent ZnO and mixed ZnWO(4)-ZnO nanostructured thin films.     

Development of high-repetition-rate laser pump/x-ray probe methodologies for synchrotron facilities

We describe our implementation of a high repetition rate (54 kHz-6.5 MHz), high power (>10 W), laser system at the 7ID beamline at the Advanced Photon Source for laser pump/x-ray probe studies of optically driven molecular processes. Laser pulses at 1.06 μm wavelength and variable duration (10 or 130 ps) are synchronized to the storage ring rf signal to a precision of ~250 fs rms. Frequency doubling and tripling of the laser radiation using nonlinear optical techniques have been applied to generate 532 and 355 nm light. We demonstrate that by combining a microfocused x-ray probe with focused optical laser radiation the requisite fluence (with <10 μJ/pulse) for efficient optical excitation can be readily achieved with a compact and commercial laser system at megahertz repetition rates. We present results showing the time-evolution of near-edge x-ray spectra of a well-studied, laser-excited metalloporphyrin, Ni(II)-tetramesitylporphyrin. The use of high repetition rate, short pulse lasers as pump sources will dramatically enhance the duty cycle and efficiency in data acquisition and hence capabilities for laser-pump/x-ray probe studies of ultrafast structural dynamics at synchrotron sources.     

基于HSGT的装备健康状态评估技术

提出了基于健康状态-广义测试相关性(health state-general test,简称HSGT)的健康状态评估技术。首先,根据维修要求将故障严重程度划分成多个离散的健康状态,再按测试输出属性,将测试划分为一系列区间值的广义测试,进而结合系统功能与结构等信息,建立系统健康状态-广义测试相关性矩阵;其次,利用贝叶斯理论,建立基于HSGT的健康状态评估推理模型;最后,使用蒙特卡洛方法生成包含8个被测单元(unit under test,简称UUT)的系统,对所提技术的有效性及可行性进行了仿真验证。结果表明,提出的健康状态评估技术能根据系统测试输出结果,及时、准确地推理出系统中各个UUT的健康状态,评估结果能在故障加剧导致的功能失效前有效触发视情维修(condition based maintenance,简称CBM)的维修决策机制。     

Image reconstruction from sparse data in synchrotron-radiation-based microtomography

Synchrotron-radiation-based microcomputed-tomography (SR-μCT) is a powerful tool for yielding 3D structural information of high spatial and contrast resolution about a specimen preserved in its natural state. A large number of projection views are required currently for yielding SR-μCT images by use of existing algorithms without significant artifacts. When a wet biological specimen is imaged, synchrotron x-ray radiation from a large number of projection views can result in significant structural deformation within the specimen. A possible approach to reducing imaging time and specimen deformation is to decrease the number of projection views. In the work, using reconstruction algorithms developed recently for medical computed tomography (CT), we investigate and demonstrate image reconstruction from sparse-view data acquired in SR-μCT. Numerical results of our study suggest that images of practical value can be obtained from data acquired at a number of projection views significantly lower than those used currently in a typical SR-μCT imaging experiment.     

基于经验模式分解和互信息的多模态图像配准

基于互信息的配准方法是目前多模态图像配准研究中的热点.提出了一种基于经验模式分解后剩余图像和互信息的多模态图像配准方法.首先通过理论分析得出通过求解剩余图像之间的变换参数即可获得原始图像之间的变换参数,从而论证了二维经验模式分解(BEMD)应用于多模态图像配准的可行性,然后给出了图像配准方法的实现步骤.典型多模态图像配准实验结果表明此方法与传统互信息法和基于小波分解结合互信息的方法相比,旋转角度估计误差可以降低1个数量级,缩放参数的估计误差也有很大降低.表明该方法获得了更高的配准精度.     

Study on electrodynamic sensor of multi-modality system for multiphase flow measurement

Accurate measurement of multiphase flows, including gas/solids, gas/liquid, and liquid/liquid flows, is still challenging. In principle, electrical capacitance tomography (ECT) can be used to measure the concentration of solids in a gas/solids flow and the liquid (e.g., oil) fraction in a gas/liquid flow, if the liquid is non-conductive. Electrical resistance tomography (ERT) can be used to measure a gas/liquid flow, if the liquid is conductive. It has been attempted to use a dual-modality ECT/ERT system to measure both the concentration profile and the velocity profile by pixel-based cross correlation. However, this approach is not realistic because of the dynamic characteristics and the complexity of multiphase flows and the difficulties in determining the velocities by cross correlation. In this paper, the issues with dual modality ECT/ERT and the difficulties with pixel-based cross correlation will be discussed. A new adaptive multi-modality (ECT, ERT and electro-dynamic) sensor, which can be used to measure a gas/solids or gas/liquid flow, will be described. Especially, some details of the electrodynamic sensor of multi-modality system such as sensing electrodes optimum design, electrostatic charge amplifier, and signal processing will be discussed. Initial experimental results will be given.     

In-process force measurement for diameter control in precision cylindrical grinding

This article shows the theory and implementation of a force measurement-based approach to controlling workpiece diameter in cylindrical grinding. A simple model proposed is used to relate infeed velocity to grinding force. The model is extended to accurately control the amount of material removed in outer diameter plunge grinding given the normal force, which may be monitored in real-time. The model incorporates the key parameters, including the structural loop stiffness, the plunge infeed velocity, and the wheel and workpiece properties. However, only the infeed velocity must be explicitly known. The contribution of this work is experimental validation that the lag between infeed and stock removal can be predicted using force feedback without a priori knowledge of the grinding system. This allows very accurate diameter control (0.25 μm of nominal), even in the presence of thermal drift, wheel wear, and machine error.     

PET/CT在肿瘤学中的应用

PET/CT技术迅速发展,很快成为医学影像诊断,特别是肿瘤诊断和研究的热点。通过将PET与CT两种技术整合到同一检查设备上,将不同性质的图像进行同机融合和比较分析,PET/CT实现对病变的解剖形态显示与功能代谢显示的互补结合。PET与CT的结合,提高对肿瘤病灶的定位和定性诊断的准确性,往往因此而改变对患者的诊疗决策。这一技术的进步不仅使得核医学领域充满活力,也引起放射医学界的极大兴趣。本文概述PET和PET/CT在肿瘤学方面的应用现状,分析PET/CT的优势与不足,并对这一技术未来的发展趋势进行展望。     

过程层析成像与多相流测量应用

过程层析成像技术(Process Tomography,简称PT)由于其非侵入与可视化等特性在医疗与工业过程等领域有广泛的应用前景,已从实验室研究进入工业应用研究阶段。本文介绍了基于光学、电学、超声以及核子敏感性原理的PT技术与多模态PT技术,并简述了PT技术在多相流测量中的应用研究方向。     

Data fusion in dual-mode tomography for imaging oil–gas two-phase flow

Process tomography (PT) techniques have been developed rapidly for visualizing the internal behavior of industrial processes, e.g. multi-phase flow measurement. Most of tomography systems employ a single measurement technique, such as computerized tomography (CT), optical tomography (OT), electrical resistance tomography (ERT) or electrical capacitance tomography (ECT). It is now possible to fit two or more tomographic systems to an industrial process. Detailed information from different modalities can be gained by inspection of separate tomographs, and the advantage of the strongest features provided by each unit can be taken. A combined tomogram can be produced of superior quality to any of the separate tomograms. To maximize the information available from the combined tomographic system, data fusion is the better option. In this paper, a dual-mode tomography system based on capacitance sensor and gamma sensor was developed to capture oil–gas two-phase flow. The two modalities can work at the same time. Two fusion methods, namely image fusion method and data fusion method, are proposed. Both simulation and static experiments for oil–gas two-phase flow were conducted. The reconstruction results of different fusion methods and modalities were compared and discussed.     

X-ray grating interferometer for materials-science imaging at a low-coherent wiggler source

X-ray phase-contrast radiography and tomography enable to increase contrast for weakly absorbing materials. Recently, x-ray grating interferometers were developed that extend the possibility of phase-contrast imaging from highly brilliant radiation sources like third-generation synchrotron sources to non-coherent conventional x-ray tube sources. Here, we present the first installation of a three grating x-ray interferometer at a low-coherence wiggler source at the beamline W2 (HARWI II) operated by the Helmholtz-Zentrum Geesthacht at the second-generation synchrotron storage ring DORIS (DESY, Hamburg, Germany). Using this type of the wiggler insertion device with a millimeter-sized source allows monochromatic phase-contrast imaging of centimeter sized objects with high photon flux. Thus, biological and materials-science imaging applications can highly profit from this imaging modality. The specially designed grating interferometer currently works in the photon energy range from 22 to 30 keV, and the range will be increased by using adapted x-ray optical gratings. Our results of an energy-dependent visibility measurement in comparison to corresponding simulations demonstrate the performance of the new setup.     

Digital-signal-processor-based dynamic imaging system for optical tomography

In this article, we introduce a dynamic optical tomography system that is, unlike currently available analog instrumentation, based on digital data acquisition and filtering techniques. At the core of this continuous wave instrument is a digital signal processor (DSP) that collects, collates, processes, and filters the digitized data set. The processor is also responsible for managing system timing and the imaging routines which can acquire real-time data at rates as high as 150 Hz. Many of the synchronously timed processes are controlled by a complex programmable logic device that is also used in conjunction with the DSP to orchestrate data flow. The operation of the system is implemented through a comprehensive graphical user interface designed with LABVIEW software which integrates automated calibration, data acquisition, data organization, and signal postprocessing. Performance analysis demonstrates very low system noise (approximately 1 pW rms noise equivalent power), excellent signal precision (<0.04%-0.2%) and long term system stability (<1% over 40 min). A large dynamic range (approximately 190 dB) accommodates a wide scope of measurement geometries and tissue types. First experiments on tissue phantoms show that dynamic behavior is accurately captured and spatial location can be correctly tracked using this system.