Multiple-energy X-ray Research Articles

Image-based finite element model stiffness and vBMD by single and dual energy CT reconstruction kernel

Single-energy quantitative computed tomography (SEQCT) provides volumetric bone mineral density (vBMD) measures for bone analysis and input to image-based finite element models (FEMs). Dual-energy CT (DECT) improves vBMD by accounting for voxel-specific material variations utilizing scans at multiple x-ray energies. vBMD is also altered by reconstruction kernel that cannot be accounted for using calibration phantoms. This study compared vBMD and FEM stiffness derived from SEQCT and DECT images reconstructed with two common kernels. SEQCT and DECT images of cadaveric shoulders (n = 10) were collected using standard (STD) and boneplus (BONE) kernels. Hounsfield Units were converted to vBMD using specimen-specific calibrations. DECT STD and BONE images were generated using an established material decomposition method with 40 and 90 keV simulated monochromatic images. A proximal humerus bone section below the anatomic neck was used for vBMD analysis and FEM generation. FEMs were loaded to 1 % apparent strain for stiffness measurements.Between STD and BONE kernel images, average vBMD differed 0.9 mgK2HPO4/cc and 4.1 mg K2HPO4/cc, in SEQCT and DECT images, respectively. Significant differences occurred in DECT images (p = 0.001). BONE reconstructed images produced higher vBMD measures across both SEQCT and DECT images. The difference between STD and BONE in both SEQCT- and DECT-based FEMs persisted, with larger estimated stiffness in BONE models. For six of the models DECT-based had higher stiffness than SEQCT-based models using the same kernel, although these models differed between STD and BONE kernels. Differences in stiffness between STD and BONE derived models were similar across image types (DECT: 17.5 kN/mm; SEQCT: 19.0 kN/mm). Stiffness values were significantly different within SECT kernels and between SEQCT BONE and DECT STD models. This study shows important differences in vBMD and FEM stiffness that occur due to CT-based imaging parameters alone. These results indicate that consistent imaging parameters should be used for vBMD analysis and FEM input to avoid systematic measurement errors.

Searching for Rapid Pulsations in Solar Flare X-Ray Data

Most studies of quasiperiodic pulsations (QPPs) in solar flares have identified characteristic periods in the 5–300 s range. Due to observational limitations, there have been few attempts to probe the <5 s period regime and understand the prevalence of such short-period QPPs. However, the Fermi Gamma-ray Burst Monitor (GBM) has observed approximately 1500 solar flares to date in high-cadence 16 Hz burst mode, providing us with an opportunity to study short-period QPPs at X-ray energies. We systematically analyze every solar flare observed by Fermi/GBM in burst mode, estimating the prevalence of QPPs in multiple X-ray energy bands. To better understand these results, we complement this with an analysis of synthetic solar flare lightcurves, both with and without oscillatory signals present. Using these synthetic lightcurves, we can understand the likely false-alarm and true-positive rates in the real solar GBM data. We do not find strong evidence for widespread short-period QPPs, indicating either a low base occurrence rate of such signatures or that their typical signal-to-noise ratios must be low—less than 1—in Fermi/GBM data. Finally, we present a selection of the most interesting potential QPP events that were identified in the GBM solar X-ray data.

Multiple energy X-ray imaging of metal oxide particles inside gingival tissues.

Periodontal disease affects over 50% of the global population and is characterized by gingivitis as the initial sign. One dental health issue that may contribute to the development of periodontal disease is foreign body gingivitis (FBG), which can result from exposure to some kinds of foreign metal particles from dental products or food. We design a novel, portable, affordable, multispectral X-ray and fluorescence optical microscopic imaging system dedicated to detecting and differentiating metal oxide particles in dental pathological tissues. A novel denoising algorithm is applied. We verify the feasibility and optimize the performance of the imaging system with numerical simulations. The designed imaging system has a focused X-ray tube with tunable energy spectra and thin scintillator coupled with an optical microscope as detector. A simulated soft tissue phantom is embedded with 2-micron thick metal oxide discs as the imaged object. GATE software is used to optimize the systematic parameters such as energy bandwidth and X-ray photon number. We have also applied a novel denoising method, Noise2Sim with a two-layer UNet structure, to improve the simulated image quality. The use of an X-ray source operating with an energy bandwidth of 5 keV, X-ray photon number of 108, and an X-ray detector with a 0.5 micrometer pixel size in a 100 by 100-pixel array allowed for the detection of particles as small as 0.5 micrometer. With the Noise2Sim algorithm, the CNR has improved substantially. A typical example is that the Aluminum (Al) target's CNR is improved from 6.78 to 9.72 for the case of 108 X-ray photons with the Chromium (Cr) source of 5 keV bandwidth. Different metal oxide particles were differentiated using Contrast-to-Noise ratio (CNR) by utilizing four different X-ray spectra.

A Novel Algorithm for Fast Measurement of Material Density in Symmetrical Objects Using X-Ray Radiography

AbstractX-ray radiography has proved to be essential in medical imaging and examination of material structures because it is noninvasive and generates images based on well-understood attenuation characteristics of materials. For radiographs of multiple overlapping materials, unraveling the individual attenuation contributions poses a problem that is commonly handled by either taking many radiographs at different object orientations for computed tomography or multiple images with different photon energies for Multiple Energy X-ray Absorptiometry (MEXA). Alternatively, to perform faster measurements, a novel algorithm has been developed to determine multimaterial systems' density. The algorithm can be effectively applied to perform measurements using only one to four radiographs of the object. A case study has been presented for a layered cylindrical object that involved sensitivity studies on image noise, X-ray generator voltage fluctuations, layer thickness measurement perturbations, and X-ray generator photon energy distribution fluctuations using simulated radiographs and density calculations using actual radiographs. The results from the simulated and experimental results were found to agree with actual density values.

Non-destructive depth profile evaluation of multi-layer thin film stack using simultaneous analysis of data from multiple X-ray photoelectron spectroscopy instruments

Non-destructive depth profile evaluation of multi-layer thin film stacks using simultaneous analysis of angle-resolved X-ray photoelectron spectroscopy data from multiple instruments is demonstrated. The data analysis algorithm, called the maximum smoothness method, was originally designed to handle data from a single XPS instrument with a single X-ray energy; in this work, the algorithm is extended to provide a simultaneous analysis tool which can handle data from multiple instruments with multiple X-ray energies. The analysis provides depth profiles for multilayer stacks that cannot be obtained by conventional data analysis methods. In this paper, metal multi-layer stack samples with total thickness greater than 10 nm are analyzed with the maximum smoothness method to non-destructively obtain depth profiles, with precise information on the chemical states of atoms in the surface layer (<2 nm) and the overall layer stack structure, which can only be obtained by analyzing the data from multiple instruments.

Experimental Evidence of Harnessed Expansion of a High-Z Plasma Using the Hollow Wall Design for Indirect Drive Inertial Confinement Fusion.

The effectiveness of a dome-shaped wall covered by a thin gold foil (hollow wall) [M. Vandenboomgaerde etal., Phys. Plasmas 25, 012713 (2018)PHPAEN1070-664X10.1063/1.5008669] in holding back the high-Z plasma expansion in a gas-filled hohlraum is demonstrated for the first time in experiments reproducing the irradiation conditions of indirect drive at the ignition scale. The setup exploits a 1D geometry enabling record of the complete history of the gold expansion for 8ns by imaging its emission in multiple x-ray energy ranges featuring either the absorption zones or the thermal emission regions. The measured expansion dynamics is well reproduced by numerical simulations. This novel wall design could now be tailored for the megajoule scale to enable the propagation of the inner beams up to the equator in low gas-filled hohlraum thus allowing the fine-tuning of the irradiation symmetry on the timescale required for ignition.

Quantitative microscale Fe redox imaging by multiple energy X-ray fluorescence mapping at the FeKpre-edge peak

AbstractFe oxidation/reduction reactions play a fundamental role in a wide variety of geological processes. In natural materials, Fe redox state commonly varies across small spatial scales at reaction interfaces, yet the approaches available for quantitatively mapping the Fe redox state at the microscale are limited. We have designed an optimized synchrotron-based X-ray spectroscopic approach that allows microscale quantitative mapping of Fe valence state by extending the Fe XANES pre-edge technique. An area of interest is mapped at nine energies between 7109–7118 eV and at 7200 eV, allowing reconstruction, baseline subtraction, and integration of the pre-edge feature to determine Fe(III)/ΣFe with 2 μm spatial resolution. By combining the Fe redox mapping approach with hyperspectral Raman mineralogy mapping, the Fe oxidation state distributions of the major mineral phases are revealed. In this work, the method is applied to a partially serpentinized peridotite with various Fe-bearing secondary mineral phases to trace the Fe transformations and redox changes that occurred during its alteration. Analysis with the Fe redox mapping technique revealed that the peridotite contained relict olivine with abundant Fe(II), while serpentine, pyroaurite, and another hydroxide phase are secondary mineral reservoirs of Fe(III). Although serpentine is not Fe-rich, it contained approximately 74% ± 14% Fe(III)/ΣFe. These analytical results are integral to interpreting the sequence of alteration reactions; serpentinization of primary olivine formed Fe(II)-rich brucite and oxidized serpentine, which could have contributed to H2 production during serpentinization. Subsequent weathering by oxidizing, CO2-bearing fluids led to the partial carbonation and oxidation of brucite, forming pyroaurite and a hydroxide phase containing dominantly Fe(III). This Fe redox imaging approach is applicable to standard petrographic thin sections or grain mounts and can be applied to various geologic and biogeochemical systems.

Radiation Oncology-External-Beam Radiation Therapy.

The application of structural shielding design techniques and goals as outlined in the National Council on Radiation Protection and Measurements Report 151, Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities (2005), continues to be the basis for treatment vault design in 2018 with some updated information. Treatment techniques have changed significantly with the dominant usage of intensity-modulated radiation therapy techniques today based on concurrent imaging. Some of the developments in linear accelerator technology over the past 15 y include flattening filter-free modes, which enable higher instantaneous dose rates; three-dimensional conformal radiation therapy resulting in potentially higher workloads since healthy tissue is spared; improved intensity-modulated radiation therapy treatment delivery systems with lower monitor units per centigray delivered than traditional step and shoot intensity-modulated radiation therapy; stereotactic body radiation therapy with higher treatment fractions and increased workloads; and increased use of stereotactic radiosurgery with conventional linear accelerators as well as robotic arm-mounted linear accelerators with higher treatment fractions. These new treatment units also incorporate multiple-energy x-ray beams (2 to 5 MV typical), which require a significant change in the specification of a workload to be used in each vault. As the equipment in radiation oncology departments has evolved to state-of-the-art modalities, the requirements for adequate radiation shielding for these modalities has become more rigorous. Architectural designs no longer depend on standard maze design rectangular rooms. Innovative layouts and utilization of multiple layers of shielding materials allow much greater flexibility in room designs. Maze-less rooms with direct-shielded doors are part of these challenging designs and are very common today. Use of multiple-density concrete blocks allows quicker construction of vaults and requires less space for the equivalent shielding provided. Combinations of high-density or normal-density concrete, steel, and lead are used in designs to make optimum use of available space and cost. Additional shielding needed at the edges of these single- or bi-parting sliding doors as well as baffle designs for heating, ventilation, and air conditioning systems and communication cable penetrations require detailed calculations. Examples of these designs will be given in this presentation. Consideration of the radiation levels around the planned vault must also include adjacent multistory buildings.

Crossover artifact in X-ray focusing imaging systems: K-edge subtraction imaging

The K-edge Subtraction (KES) imaging method is a very powerful synchrotron method which allows functional imaging of biological subjects. KES gives a simultaneous image of the contrast element and an anatomical image from the same data set. For biological subjects, an imaging system that uses focused multiple (two or more) x-ray energy beams to form the images, reduces motion artifact that can be misleading. However, the crossing of beams gives rise to another artifact, termed the “crossover” artifact, if the subject is not at the focus or is spatially extended around the focus. This artifact is addressed in this paper for KES which uses multiple x-ray energy focused beams. The development of multiple energy imaging systems have shown a great deal of utility in extracting multiple contrast materials. Nevertheless, the need for reduction of the crossover artifact is essential for the effective use of these systems for imaging of biological subjects, which will help prevent unnecessary re-imaging, reduce unusable images and dose to the subjects. A unified approach to modeling and reducing of crossover artifact in multiple x-ray energy KES is presented.

Use of Kramers-Kronig relation in phase retrieval calculation in X-ray spectro-ptychography.

Coherent diffraction imaging (CDI) is a method for reconstructing the complex-valued image of an object from diffraction intensities by using iterative phasing methods. X-ray ptychography is a scanning type of CDI using X-rays, allowing us to visualize the complex transmission function of an extended specimen. We here propose the use of the Kramers-Kronig relation (KKR) as an additional constraint in phase retrieval algorithms for multiple-energy X-ray ptychography using the absorption edge of a specific element. A numerical simulation showed that the speed of convergence was increased by using the improved algorithm with the KKR. We successfully demonstrated its usefulness in a proof-of-principle experiment at SPring-8. The present algorithm is particularly useful for imaging X-ray absorption fine structures of a specific element buried within thick samples by hard X-ray spectro-ptychography.

Multiple energy synchrotron biomedical imaging system

A multiple energy imaging system that can extract multiple endogenous or induced contrast materials as well as water and bone images would be ideal for imaging of biological subjects. The continuous spectrum available from synchrotron light facilities provides a nearly perfect source for multiple energy x-ray imaging. A novel multiple energy x-ray imaging system, which prepares a horizontally focused polychromatic x-ray beam, has been developed at the BioMedical Imaging and Therapy bend magnet beamline at the Canadian Light Source. The imaging system is made up of a cylindrically bent Laue single silicon (5,1,1) crystal monochromator, scanning and positioning stages for the subjects, flat panel (area) detector, and a data acquisition and control system. Depending on the crystal’s bent radius, reflection type, and the horizontal beam width of the filtered synchrotron radiation (20–50 keV) used, the size and spectral energy range of the focused beam prepared varied. For example, with a bent radius of 95 cm, a (1,1,1) type reflection and a 50 mm wide beam, a 0.5 mm wide focused beam of spectral energy range 27 keV–43 keV was obtained. This spectral energy range covers the K-edges of iodine (33.17 keV), xenon (34.56 keV), cesium (35.99 keV), and barium (37.44 keV); some of these elements are used as biomedical and clinical contrast agents. Using the developed imaging system, a test subject composed of iodine, xenon, cesium, and barium along with water and bone were imaged and their projected concentrations successfully extracted. The estimated dose rate to test subjects imaged at a ring current of 200 mA is 8.7 mGy s−1, corresponding to a cumulative dose of 1.3 Gy and a dose of 26.1 mGy per image. Potential biomedical applications of the imaging system will include projection imaging that requires any of the extracted elements as a contrast agent and multi-contrast K-edge imaging.

Multiple-wavelength resonant fluctuation x-ray scattering

A multiple-wavelength resonant fluctuation x-ray scattering approach is proposed for element-specific imaging of nanoscale objects in random ensembles with short positional and rotational relaxation times. It is shown, that by applying x-ray cross-correlation analysis in combination with iterative phase retrieval to the scattering data measured at multiple x-ray energies near an absorption edge of a substance, it is possible to image the nanoscale structure of an individual object with chemical sensitivity. The elemental distribution in distinct two-component model nanostructures was reconstructed using the simulated scattering data from two-dimensional random ensembles of particles. The approach might be especially advantageous for structural studies at x-ray free electron lasers.

Evaluation of multiple-scale 3D characterization for coal physical structure with DCM method and synchrotron X-ray CT.

Multiscale nondestructive characterization of coal microscopic physical structure can provide important information for coal conversion and coal-bed methane extraction. In this study, the physical structure of a coal sample was investigated by synchrotron-based multiple-energy X-ray CT at three beam energies and two different spatial resolutions. A data-constrained modeling (DCM) approach was used to quantitatively characterize the multiscale compositional distributions at the two resolutions. The volume fractions of each voxel for four different composition groups were obtained at the two resolutions. Between the two resolutions, the difference for DCM computed volume fractions of coal matrix and pores is less than 0.3%, and the difference for mineral composition groups is less than 0.17%. This demonstrates that the DCM approach can account for compositions beyond the X-ray CT imaging resolution with adequate accuracy. By using DCM, it is possible to characterize a relatively large coal sample at a relatively low spatial resolution with minimal loss of the effect due to subpixel fine length scale structures.

Time-resolved multispectral X-ray imaging with multi-channel Kirkpatrick-Baez microscope for plasma diagnostics at Shenguang-II laser facility

A time-resolved multispectral X-ray imaging approach with new version of multi-channel Kirkpatrick-Baez (KB) microscope is developed for laser plasma diagnostics at the kilojoule-class Shenguang-II laser facility (SG-II). The microscope uses a total external reflection mirror in the sagittal direction and an array of multilayer mirrors in the tangential direction to obtain multiple individual high-resolution, highthroughput, and quasi-monochromatic X-ray images. The time evolution of the imploded target in multiple X-ray energy bands can be acquired when coupled with an X-ray streak camera. The experimental result of the time-resolved 2.5 and 3.0 keV dual-spectral self-emission imaging of the undoped CH shell target on SG-II is given.

Oxidation states study of nickel in solid oxide fuel cell anode using x-ray full-field spectroscopic nano-tomography

Identifying the chemical state and coupling with morphological information in three dimensions are of great interest in energy storage materials, which typically involve reduction-oxidation cycling and structural evolution. Here, we apply x-ray nano-tomography with multiple x-ray energies to study oxidation states of nickel (Ni) and nickel oxide phases in Ni-yttria-stabilized zirconia (YSZ), a typical anode material of solid oxide fuel cells (SOFC). We present a method to quantitatively identify the nickel-based oxides from Ni-YSZ anode composite, and obtain chemical mapping as well as associated microstructures at nanometer scale in three dimensions. NiO particles manually placed on a Ni-YSZ composite anode were used for validation of the method, while no nickel oxides were found to be present within the electrode structure as remnants of the cell fabrication process. The application of the method can be widely applied to energy storage materials including SOFCs, Li-ion batteries, and supercapacitors, as well as other systems for oxidation and reduction study.

Characterization of DNA and RNA Ion Atmospheres Using Multiple-Energy Asaxs

The number and spatial distribution of small positively-charged ions around highly negatively charged DNA or RNA contribute to the free energy of binding in vitro and in vivo. However, the majority of charge compensating ions around nucleic acids forms a diffuse counterion “cloud” that is not amenable to investigation by traditional methods that rely on rigid structural interactions. With 2 x-ray energies, one near and the other 100 eV away from the ion absorption edge, we have successfully used Anomalous Small-Angle X-ray Scattering (ASAXS) to compare and differentiate the ion spatial distribution around comparably sequenced short DNA and RNA helices. Here, we present further information gained when using multiple x-ray energies (up to 5) in an ASAXS experiment. We describe proper treatment of multiple-energy SAXS data including absolute SAXS intensity calibration and measurement of scattering factors from x-ray fluorescence. We discuss the strengths and limitations of this approach and derive useful parameters in depicting the nucleic acid ion atmosphere.

Cramér–Rao lower bound of basis image noise in multiple-energy x-ray imaging

We present an analytical method to compute the basis image noise in the context of multi-energy x-ray imaging based on the Cramér–Rao lower bound (CRLB). The proposed formalism extends the original idea of Alvarez and Macovski (1976 Phys. Med. Biol. 21 733) to estimate the noise in the photo-effect and Compton-effect basis images in the case of dual-energy imaging. It includes an arbitrary number of independent, spectrally distinct attenuation measurements and also goes beyond the two-dimensional decomposition of the attenuation, including, e.g., a contrast agent as a third basis material. To illustrate our method, we consider three simple applications. The first application is to study the influence of the exact values for the energy thresholds on the basis image noise for a binned photon-counting system. The second application relates to the same detector system as the first and is an investigation of the dependence of the basis image noise on the energy resolution of the detector system. Finally, the third application provides an example for the case of an energy-integrating detector: the aim is to optimize the front-scintillator layer thickness of a dual-crystal detector for dual-energy imaging. The CRLB is used to minimize the noise of a photo-effect/Compton-effect basis material decomposition.

Application of X-ray computed tomography to soil science: A literature review

The study of the spatial configuration of soil, in its complexity, requires an understanding of the interrelations and interactions between the diverse soil constituents, at various levels of organization. Investigations of the spatial arrangement of the mineral and organic components of soil have benefited from the development of techniques for structural analysis. X-ray computed tomography (CT) is a non-destructive and non-invasive technique that has been successfully used for three-dimensional (3D) examination of soil. Valuable information has been obtained by the application of CT for the description and quantitative measurements of soil structure elements, especially of soil pores and pore network features. In many studies, X-ray CT has been used to investigate the hydro-physical characteristics of the soil, in a functional and temporal manner. A dynamic approach has also been utilized in the evaluation of the biotic factor influence on soil. The analysis of soil solid phases, by X-ray CT, has been challenging due to the similar X-ray attenuation of different solid constituents. However, the use of multiple X-ray energy levels has facilitated the discrimination of minerals in soil. The aim of this review and synthesis is to offer a perspective on the major issues related to application of the technique, general attempted solutions and possible directions in the utilization of X-ray CT in soil research. Relevant scanning parameters, procedures for CT image reconstruction, algorithms for the quantification of soil characteristics and results are presented for each type of application. Key words: X-ray computed tomography, energy level, spatial resolution, segmentation, soil mineral and organic constituents, soil physical and hydro-physical properties, soil biota

Reconstruction of atomic images from multiple-energy x-ray holograms of FePt films by the scattering pattern matrix method

The scattering pattern matrix (SPM) method, in combination with multiple-energy holographic patterns, can be used to successfully reconstruct Pt atomic images in FePt epitaxial films, that are almost free from the artifacts that often appear in the images reconstructed using the Barton algorithm. The difference in the chemical short-range-order structure in two FePt films grown at different temperatures was clearly observed. The present method provides us a concrete breakthrough for a quantitative analysis of a three-dimensional local atom arrangement around a certain element in a single crystal without any preliminary knowledge of its structure.

Inverse Fourier analysis in x-ray fluorescence holography

X-ray fluorescence holography (XFH) is a promising tool for determing the local structures around specified elements. To obtain accurate interatomic distances, we applied inverse Fourier analysis, which has often been used to investigate extended x-ray absorption fine structures, to multiple energy x-ray holograms. The interatomic distances of neighboring atoms around a fluorescing atom were estimated from the 16 experimental holograms of a Au single crystal and most of them were in good agreement with the actual values within an error of 0.3%. The use of inverse Fourier analysis improves the XFH for the evaluation of quantitative local lattice distortion around impurities in single crystals.