Advances in 3D ion micro-tomography

A new method for three dimensional tomographic analysis of micro-samples is presented. The technique is capable of accurately calculating the mass density and composition distribution of a sample, using the data measured from a STIM and PIXE tomography experiment. The technique solves for the effects of the energy dependence of the proton stopping-power and X-ray production cross-section. It also incorporates X-ray attenuation for a cone geometry between the sample and X-ray detector. A priori information about low Z elements is easily incorporated into the technique. The reconstruction of the mass density and composition of a phantom is shown.     

Singular Value Decomposition Combined With Analytical Method for Tokamak Plasma Tomography

Several arrays of soft X-ray detectors are used with the Fourier expansion for angular direction and Zernicke polynomial on radial direction during an analytical method tomography. A truncation of two expansions is necessary. We used singular value decomposition in order to solve the set of equations. This technique reconstructs better images of tomography.     

Algorithmic techniques for quantitative Compton tomography

Compton tomography is a non-destructive technique that allows one to reconstruct the spatial distribution of the electronic density of the sample analyzed. This information is complementary to the absorption coefficient distribution at a given energy, which can be obtained by a more conventional transmission tomography. However, the reconstruction algorithms used in Compton tomography are different and more complex than those used in transmission tomography. This is mainly due to the absorption of the X-ray photons along the path from the source to the interaction point and from the interaction point to the detector. Only a few of the reconstruction algorithms reported in the literature take absorption corrections into account, and the problems of a quantitative reconstruction have seldom been discussed. In this paper a new kind of reconstruction algorithm is described and the first results are reported and discussed.     

White beam synchrotron topography using a high resolution digital X-ray imaging detector

X-ray topography is a well known imaging technique to characterise strain and extended defects in single crystals. Topographs are typically collected on X-ray films. On the one hand such photographic films show a limited dynamic range and the production of films will be discontinued step by step in the near future. On the other hand new imaging detectors improved for X-ray tomography become more and more attractive even for topography because of increasing resolution, dynamic range, speed and active area. In this paper we report about the upgrade of the TOPO-TOMO beamline at the synchrotron light source ANKA, Research Centre Karlsruhe, with a high resolution digital camera for the topography use.     

X射线工业CT散射修正

X射线工业CT（ICT）依赖准直器压低散射光子存在实际困难和不足。为解决这一问题，需采用相应的修正软件加以校正。文章从理想的模型出发，近似推导透射式ICT中散射X光子的理论计算公式，并把计算结果与实验结果进行比较。比较结果表明，两者吻合较好。据此，文章给出了散射光子软件修正的可行性方案。      

Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies, we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focusing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm × 1.5 mm × 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target. The CT system achieves up to 7000 frames per second with a spatial resolution of 1 mm. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.     

Soft X-ray ptychography method at SSRF

Ptychography is a diffraction-based X-ray microscopy technique in which an extended sample is scanned by a coherent beam with overlapped illuminated areas and complex transmission function of the sample is obtained by applying iterative phase retrieval algorithms to the diffraction patterns recorded at each scanned position.It permits quantitatively imaging of non-crystalline specimens at a resolution limited only by the X-ray wavelength and the maximal scattering angle detected.In this paper,the development of soft X-ray ptychography method at the BL08U1A beamline of Shanghai Synchrotron Radiation Facility is presented.The experimental setup,experimental parameters selection criteria,and post-experimental data analyzing procedures are presented in detail with a prospect of high-resolution image reconstruction in real time.The performance of this newly implemented method is demonstrated through the measurements of a resolution test pattern and two real samples:Pt-Co alloy nanoparticles and a breast cancer cell.The results indicate that strong scattering specimens can be reconstructed to sub-20 nm resolution,while a sub-25 nm resolution for biological specimens can be achieved.     

First results on ion micro-tomography at LIPSION

At the nanoprobe LIPSION ion micro-tomography can be used to determine the 3D distribution information of a sample’s mass density and elemental composition. For ion micro-tomography the two analytical techniques scanning transmission ion microscopy tomography (STIM-T) and particle induced X-ray emission tomography (PIXE-T) are combined. The required data are collected in two consecutive series of measurements, during which the sample is rotated by 180°/360° in small steps. Because all ions have to traverse the sample, the upper limit of the sample size is given by the range of the ions in the material. The tomogram is obtained using the discrete image space reconstruction algorithm (DISRA) by Sakellariou (1997) [1]. This algorithm iteratively corrects a sketchy initial tomogram estimated from the experimental reconstruction – obtained by backprojection of filtered projections (BFP) – and an a priori elemental composition. The necessary correction factors are calculated comparing the reconstruction of the experimental data with the reconstruction of simulated data. For the simulated data sets of STIM projections and PIXE maps are computed from the tomogram. These data sets are proceeded with the BFP algorithm to get simulated reconstruction data. Using the DISRA for ion micro-tomography, one can benefit from the high resolution of STIM-T by transferring it to the elemental distribution given by PIXE-T. This article presents first results of this technique applied on a phantom at the LIPSION facility.     

Imaging of voids due to deformation in alloy steel using micro-focus X-ray beam

A micro-focus X-ray beam source along with computed tomography technique has been used to image the voids developed during tensile deformation in alloy steel used as structural material for nuclear power plant components. The technique was successful to characterize the internal void structure in the necked region of CrMoV type steel in terms of the size, distribution and volume fraction. The void volume fraction was found to be about 0.03% in a volume of 1.4 mm³ of the necked region reduced in diameter by 32% as a result of tensile deformation.     

Measurement of focal spot size in a 5.5 MeV linac

High energy X-ray beams allow to perform analysis on different materials and objects of relevant interest that cannot be investigated with conventional X-ray sources. A 5.5 MeV endpoint energy bremsstrahlung source has been characterized by evaluating the size of X-ray emitting area. In order to perform a proper characterization, an ‘ad hoc’ slit-camera has been designed and a specific technique has been adopted. Due to the characteristics of the beam, a highly attenuating slit with variable aperture has been designed using Monte Carlo simulations of the X-ray beam and set up. Since the slit camera is far from the ideal model (negligible X-ray transmission and very thin aperture), a whole set of image profiles of the slit at different width sizes have been acquired and analyzed. Imaging correction procedures and data fitting lead to satisfactory experimental results according to the theoretical model.     

CT image correction for beam hardening using simulated projectiondata

A general beam-hardening correction technique is presented. Knowledge of the CT (computerized tomography) scanner X-ray spectrum is necessary. This postreconstruction method does not require the original projection data. Simulated projections through an uncorrected reconstructed image are used to correct for beam hardening. Errors in the mean linear attenuation coefficient are decreased from 30% to 5% with virtual elimination of the visual streaking artifact. The theoretical image improvement equals that of projection linearization postreconstruction methods using the original projection data. The correction is limited to cases where the material causing the beam hardening is contained within the reconstruction space     

Energy-dependent systematic errors in dual-energy X-ray CT

Dual-energy X-ray computed tomography (DECT) is a technique which is designed to allow the determination of energy-independent material properties. In this study, results of a computer simulation show that energy-dependent systematic errors exist in the values of attenuation coefficients synthesized using the basis material decomposition technique with acrylic and aluminum as the basis materials, especially when a high atomic number element such as iodine (e.g., from radiographic contrast media) is present in the body. The errors are reduced when an acrylic and an iodine-water mixture are used as the basis materials. The authors propose a simple theoretical model for the calculation of energy-dependent systematic errors using effective energies at the lower and higher energy windows of the X-ray spectrum used in the DECT system. The calculated errors agree well with the errors observed in the simulation. These results suggest that the observed systematic errors are predominantly due to the energy dependence of the basis material coefficients     

Selection of the experimental conditions for white-light SRIXE measurements

Synchrotron-radiation-induced X-ray emission has enormous potential as a technique for trace-element analysis. To fully utilize the many advantages of SRIXE measurements, one must optimize the experimental conditions. In this paper the problems associated with the selection of experimental conditions are discussed in theory. In addition, examples of experimental work done at the National Synchrotron Light Source at Brookhaven National Laboratory, USA are presented.     

Beam and image experiment of beam deflection electron gun for distributed X-ray sources

Distributed X-ray sources comprise a single vacuum chamber containing multiple X-ray sources that are triggered and emit X-rays at a specific time and location. This process facilitates an application for innovative system concepts in X-ray and computer tomography. This paper proposes a novel electron beam focusing, shaping,and deflection electron gun for distributed X-ray sources.The electron gun uses a dispenser cathode as an electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflection. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. Two identical half-rectangle opening electrodes are controlled by adjusting the potential of the two electrodes to control the electron beam trajectory, and then, multifocal spots are obtained on the anode target. The electron gun can increase the spatial density of the distributed X-ray sources, thereby improving the image quality. The beam experimental results show that the focal spot sizes of the deflected(deflected amplitude 10.5 mm)and non-deflected electron beams at full width at half maximum are 0.80 mm 90.50 mm and 0.55 mm 90.40 mm, respectively(anode voltage 160 kV; beam current 30 mA). The imaging experimental results demonstrate the excellent spatial resolution and time resolution of an imaging system built with the sources, which has an excellent imaging effect on a field-programmable gate array chip and a rotating metal disk.     

4B9A束线单色器的改进及在线调试

报导了北京同步辐射装置4B9A束线前期改造中单色器的改进安装调试情况,并对单色器出高的变化和实际光强进行了测量。结果表明：4B9A束线的前期改造已解决了单色器出高的变化问题,为衍射站和小角站的工作创造了条件。     

Attenuation correction of polychromatic L-shell X-ray fluorescence computed tomography imaging

Polychromatic L-shell X-ray fluorescence computed tomography is a promising imaging technique to explore the element distribution of the sample. However, the image quality of large samples would be decreased dramatically due to the present of the self-absorption. In this investigation, an attenuation correction algorithm based on theories related to X-ray fluorescence was proposed. With this method, the attenuation coefficients at the incident energies were expressed as a function of known X-ray energies and unknown platinum concentrations. Then the attenuation coefficients were calculated based on the theories and added in the contribution value of the pixel in Maximum Likelihood Expectation Maximization reconstruction method. The element distributions can be got through continuous iterations. Finally, the feasibility of this method was tested by Monte Carlo simulation. The results indicated that, for a 4-mm diameter phantom containing an object of 2 mm in diameter with 0.10 wt% platinum solutions, the CNR of reconstructed images increased from 53.5 to 203.8 after attenuation correction while the relative error decreases from 97% to 2%.     

Scanning transmission ion microscopy tomography at the Leipzig nanoprobe LIPSION

Scanning transmission ion microscopy (STIM) of joint cartilage could visualise single collagen fibrils. Thus, answers to the controversial questions of their alignment could be given. However, the fibrils form three-dimensional structures that are not yet fully disclosed. STIM tomography is needed to give more detailed information. The size of the structures requires a challenging resolution of about 100 nm. The first STIM tomographic experiment has been performed at the Leipzig nanoprobe LIPSION. 360 projections of a cartilage sample (30 μm×32 μm×10 μm) were taken. The pixel resolution was 250×250 pixels for each projection. The data set was reconstructed at MARC Melbourne using the backprojection of filtered projections technique. The data show the feasibility of STIM tomography in cartilage research. However, experimental inaccuracies (rotational displacement and magnetic stray fields) have limited the resolution thus far. Improvements in the experimental set-up will lead to higher resolution.     

Algorithms for three-dimensional chemical analysis via multi-energy synchrotron X-ray tomography

The conversion of X-ray tomography images into three-dimensional chemical composition requires accurate mass absorption values, high-quality images, and a robust fitting algorithm. The least-squares fits of the images to a three-dimensional chemical composition can proceed with several different options such as minimal vs. over-determined and/or constrained parameters. This project has investigated the impact of XAFS features and a limited CCD dynamic range. These simulated results are compared to a recent experimental project in which synchrotron X-ray tomography was used to image a polymer blend, and from those images, calculated three-dimensional chemical composition maps of the two-component flame retardant, a brominated phthalimide dimer, Saytex^™ BT-93 and a synergist, antimony(III) oxide (Sb₂O₃).     

Absolute mass thickness determination of thin samples by X-ray fluorescence analysis

An absolute method for mass thickness determination of thin samples by X-ray fluorescence analysis has been developed. The method is based on the experimental determination of the fluorescence intensities of the sample's constituent elements in reflection and transmission geometries. The samples studied were elemental and compound foils. A set of numerical calculations, Monte Carlo simulations and experimental measurements with thin samples including super-conductor monocrystals were performed with very good results. The range of thicknesses which can be determined by the proposed technique depends on the sample's composition, the excitation energy and the geometrical arrangement.