High-resolution X-ray Imaging Research Articles

Advanced imaging for research applied to digital dentistry

The production, by 3D printing, of optimized titanium meshes and biphasic calcium phosphate scaffolds for bone regeneration as well as the 3D printing of zirconia with high mechanical performances for dental restorations are between the most relevant challenges in digital dentistry. Our research group offers a complete set of advanced imaging and mechanical analysis to achieve these goals. We are currently using high-resolution X-ray tomography (microCT), electron microscopy and several material testing devices, all available at our laboratories, to test the following 3D-printed samples: (1) titanium meshes with different geometries; (2) zirconia blocks; (3) biphasic calcium phosphate scaffolds. The titanium meshes and the biphasic calcium phosphate scaffolds are currently under analysis with the objective to detect, by microCT imaging, the microarchitecture and eventual 3D defects before and after mechanical tests simulating the masticatory process. Moreover, the mechanical performance of 3D-printed versus milled zirconia blocks was also observed, before and after the application of compressive load, with the aim to investigate the microstructural characteristics of samples printed by Lithography-based Ceramic Manufacturing (LCM). Further, 60% of the 3D-printed samples were observed to have a mechanical behavior overlapping with the milled samples. The early fracture of the remaining 3D-printed samples could be due, as shown by electron microscopy, to the presence of pores of large dimensions and regular shape in the bulk. We are realizing an innovative working flow-chart for a reliable and complete characterization of these innovative 3D-printed biomaterials.

Heterochrony and parallel evolution of echinoderm, hemichordate and cephalochordate internal bars.

Deuterostomes comprise three phyla with radically different body plans. Phylogenetic bracketing of the living deuterostome clades suggests the latest common ancestor of echinoderms, hemichordates and chordates was a bilaterally symmetrical worm with pharyngeal openings, with these characters lost in echinoderms. Early fossil echinoderms with pharyngeal openings have been described, but their interpretation is highly controversial. Here, we critically evaluate the evidence for pharyngeal structures (gill bars) in the extinct stylophoran echinoderms Lagynocystis pyramidalis and Jaekelocarpus oklahomensis using virtual models based on high-resolution X-ray tomography scans of three-dimensionally preserved fossil specimens. Multivariate analyses of the size, spacing and arrangement of the internal bars in these fossils indicate they are substantially more similar to gill bars in modern enteropneust hemichordates and cephalochordates than to other internal bar-like structures in fossil blastozoan echinoderms. The close similarity between the internal bars of the stylophorans L. pyramidalis and J. oklahomensis and the gill bars of extant chordates and hemichordates is strong evidence for their homology. Differences between these internal bars and bar-like elements of the respiratory systems in blastozoans suggest these structures might have arisen through parallel evolution across deuterostomes, perhaps underpinned by a common developmental genetic mechanism.

Alveolar Bone Remodeling with or without Collagen Filling of the Extraction Socket: A High-Resolution X-ray Tomography Animal Study

The healing process of the tooth extraction socket often leads to significant resorption of the alveolar bone, eventually causing clinical difficulties for future implant-supported rehabilitations. The aim of the present animal study was to evaluate alveolar bone remodeling after tooth extraction in a rabbit model, either with or without the use of a plain collagen plug inside the socket, by means of micro-computed tomography. The study included the micro-tomography analysis of 36 rabbits’ incisor extraction sockets, either left empty or filled with a collagen plug. All animals were euthanized in a staggered manner, in order to address molecular, histologic, and radiographic analyses at different time-points, up to 90 days after surgery. The three-dimensional evaluation was carried out using micro-computed tomography technology on excised bone blocks including the alveolus and the contralateral bone. Both linear and volumetric measures were recorded: the percentage of bone volume change (ΔBV) within the region of interest was considered the primary endpoint of the study. The micro-CT analysis revealed mean volumetric changes of −58.1% ± from baseline to 3 months for the control group, and almost no bone loss for the test group, −4.6%. The sockets treated with the collagen plug showed significantly less dimensional resorption, while the natural-healing group showed an evident collapse of the alveolar bone three months after extraction surgery.

Directional-Sensitive X-ray/Gamma-ray Imager on Board the VZLUSAT-2 CubeSat for Wide Field-of-View Observation of GRBs in Low Earth Orbit

We present a miniaturized and wide field-of-view X-ray and Gamma-ray imager consisting of a segmented 2D optics-collimator coupled to the high-sensitivity semiconductor pixel detector Timepix equipped with a high-Z sensor (CdTe 2000 μm thick). The compact payload has been deployed in low-Earth orbit (LEO) onboard the 3U Cubesat VZLUSAT-2 which was launched on 13 January 2022. The instrument is designed to verify small spacecraft borne observation in open space of hard X-ray and Gamma-ray sources both of celestial and atmospheric origin. High-resolution spectral-sensitive X-ray and Gamma-ray images are provided with enhanced event discrimination and wide field-of-view up to 60°. Description of the instrument together with response evaluation and tests in ground with well-defined sources are presented. The intended observational plan for in-orbit measurements is outlined along with astrophysical goals and issues.

Optimization-based algorithm for x-ray super-resolution imaging

An optimization-based algorithm is introduced to achieve the subpixel resolution in x-ray imaging. In this approach, the image captured by a detector is to be considered as a degradation of a high-resolution image. The inverse problem of the degradation is formulated as an optimization program. Through solving the cost function with Chambolle–Pock (CP) algorithm, we can reconstruct the subpixel image from multiple images shifted with subpixel precision. Numerical studies indicate that the iterative algorithm can numerically accurately invert the degradation. A set of x-ray imaging experiments were performed, and some structural information can be found in the reconstruction of the high-resolution image but not existing in the original image data. It would have potential applications in x-ray high-resolution imaging and industrial detection.

Applicability of Large-Area Single-Photon Counting Detectors Timepix for High-Resolution and High-Contrast X-Ray Imaging of Biological Samples

High-resolution X-ray imaging techniques, usually known as microradiography and micro-computed tomography (CT), have become highly required and frequently used tools for biology, biomedical and preclinical research. State-of-the-art micro-CT scanners are capable of achieving a spatial resolution of few micrometers or even less, thanks to the constant development of compact microfocus X-ray sources together with simultaneous progress in detector technologies. The current standard in X-ray detection is a digital imaging device containing read-out circuitry coupled with a scintillation sensor. Such detectors are available in a variety of different sizes, and are easy to use and relatively affordable. Nevertheless, the mentioned technology suffers from inherent limitations like, for example, undesirable generation of dark current, that compromise the quality of the provided data. This work demonstrates the applicability of Timepix large-area hybrid-pixel photon-counting detectors (PCDs) for high-resolution X-ray imaging in biology research. Photon-counting detection technology provides dark-current-free quantum-counting operation. Therefore, an enhanced contrast-to-noise ratio of the acquired data is achieved. Furthermore, the biased semiconductor sensor achieves almost ideal point-spread function (PSF) resulting in images with high spatial-resolution. Both above-mentioned features make PCDs to be excellent tools for high-resolution X-ray imaging especially for samples with low intrinsic absorption contrast. We evaluated the imaging performance of large-area Timepix detectors compared to a state-of-the-art flat-panel detector dedicated for high-resolution X-ray imaging. The presented data demonstrate the versatility of the used detectors as it covers a wide range of samples from laboratory animals to single-cell marine organisms.

In-vivo imaging of a mouse by detecting bremsstrahlung X-rays from 14C using a La-GPS imaging system

ABSTRACT Imaging of 14C outside of the subject is considered to be difficult because it is a radionuclide that emits only low-energy beta particles. However, we found that bremsstrahlung X-rays form 14C could be imaged from outside of subjects and is thus applicable to in vivo small animal imaging. We developed a high-resolution low-energy X-ray imaging system using a (Gd, La)2Si2O7:Ce(La-GPS) plate combined with a flat panel photomultiplier tube (FP-PMT) for in vivo imaging of a mouse to detect the X-rays from a 14C solution administered. Without using a parallel hole collimator, accumulated 14C in the mouse’s abdomen was imaged in 1 min and dynamic in vivo imaging was possible although the spatial resolution was moderate. With a parallel hole collimator, 14C in the abdomen was obtained with a higher spatial resolution with a 60-min acquisition time. We conclude that in vivo imaging of 14C is possible by using the developed high-resolution La-GPS imaging system and may be promising for molecular imaging research.

Development of a quasi-coaxis dual-energy flat spectral response X-ray imaging instrument for measuring hotspot electron temperature.

The measurement of hotspot electron temperature is a paramount technique of implosion physics research in inertial confinement fusion. This study proposes a novel quasi-coaxis dual-energy flat spectral response high-resolution X-ray imaging instrument comprising a dual-channel total-reflection Kirkpatrick-Baez microscope and two flat non-periodic multilayer mirrors, which can image at 6.4 ± 0.5 and 9.67 ± 0.5 keV simultaneously. Various theoretical simulations were performed to verify the performance and feasibility of the imaging instrument, which was assembled and characterized in a laboratory. Experimental results show that the imaging instrument could achieve a high spatial resolution of 5 µm in a ± 150 µm field of view (FOV), the root mean square(RMS) deviation values of the measured reflection efficiency are 1.71% and 1.82% for the 6.4 keV and 9.67 keV imaging channels, respectively, in the ± 150 µm FOV.

Gate offset and emitter design effects of triode cold cathode electron beams on focal spot sizes for x-ray imaging techniques

We report on the structural effects of a carbon nanotube based cold cathode electron beam (C-beam) module on focal spot sizes (FSSs) for high resolution x-ray imaging applications without additional focusing components. A simple combination of vertically aligned carbon nanotubes and gate mesh structure achieved FSS of 252 and 410 μm for longitudinal and transverse directions, respectively. As design parameters of the modules, gate offsets, gate hole pitch, and emitter area effects of C-beam modules on FSS were optimized. We expect that our simple but sophisticated C-beam module structure will pave next generation x-ray devices not only for high quality x-ray imaging but cost-effective ways for mass production.

Revealing melt flow instabilities in laser powder bed fusion additive manufacturing of aluminum alloy via in-situ high-speed X-ray imaging

Laser metal additive manufacturing technologies enable the fabrication of geometrically and compositionally complex parts unachievable by conventional manufacturing methods. However, the certification and qualification of additively manufactured parts are greatly hindered by the stochastic melt flow instabilities intrinsic to the process, which has not been explicitly revealed by direct observation. Here, we report the mechanisms of the melt flow instabilities in laser powder bed fusion additive manufacturing process revealed by in-situ high-speed high-resolution synchrotron X-ray imaging. We identified powder/droplet impact, significant keyhole oscillation, and melting-mode switching as three major mechanisms for causing melt flow instabilities. We demonstrated the detrimental consequences of these instabilities brought to the process, and presented new understanding on the melt flow evolution and keyhole oscillation. This work provides critical insights into process instabilities during laser metal additive manufacturing, which may guide the development of instability mitigation approaches. The results reported here are also important for the development and validation of high-fidelity computational models.

Gas–surface interactions in lightweight fibrous carbon materials

We investigate reactive and non-reactive scattering of hyperthermal beam of gas particles within highly porous carbon-fiber preform using particle-based numerical simulations. High-resolution X-ray tomography images of the microstructure is used to resolve its complex fiber network. The gas–surface interaction is studied at material temperatures up to 2000 K, typical of hypersonic aero-thermal environments. We extended a detailed surface chemistry model for oxidation of vitreous carbon to carbon-fiber materials. The model agrees well with experiments and predicts increasing oxidation product flux with larger porosities. Higher porosities lead to a larger fraction of thermalized argon atoms and greater mole fraction of CO for the oxygen beam due to greater penetration of the beam into the microstructure. It is found that a 6% porosity increase results in higher mole fractions of CO and lower amounts of O, with differences of around 10% of the total product flux. Furthermore, we construct an effective oxidation model with porosity-dependent rates that inherently accounts for the characteristics of the material microstructure and its varying porosity. Comparison of full microstructure simulation results and the effective model applied to a flat surface showed excellent agreement, thus suggesting that the model can be used directly in computational fluid dynamics codes.

High-resolution dual-energy sixteen-channel Kirkpatrick–Baez microscope for ultrafast laser plasma diagnostics

High-resolution x-ray imaging diagnostics play a crucial role in fundamental research, such as inertial confinement fusion (ICF) and high-energy density physics (HEDP). Plasma signals are typically characterized by small scales, rapid evolution, and spectral complexity. These characteristics make it essential to develop x-ray diagnostics optics with high spatial resolution, collection efficiency, and spectral resolution. These requirements can be met using a combination of a high-resolution multi-channel Kirkpatrick–Baez (KB) microscope with spectrum-resolved multilayers and a time-resolved framing camera. This study describes the optical and multilayer design of a dual-energy sixteen-channel KB microscope. The calibrated results of online and offline imaging are shown. By utilizing a dual-energy multi-channel KB microscope, high-resolution backlighting and self-emission x-ray imaging can be realized and detailed information related to plasma density and temperature can be simultaneously obtained.

Scintillating thin film design for ultimate high resolution X-ray imaging

Energy deposition in scintillating screens effects on the high resolution X-ray imaging.

Terbium-doped LiYbF4nanomaterial-based scintillator responding to X-rays with high-resolution imaging applications

As a new scintillation material, LiYbF4nanocrystals exhibit high stability and strong absorption of X-rays, and appear competitive in high-resolution X-ray imaging with a spatial resolution of 20 LP mm−1(MTF = 0.35).

Designing a toroidal crystal for monochromatic X-ray imaging of a laser-produced He-like plasma

Abstract In this study, a toroidal quartz ( $20\overline{2}3$ ) crystal is designed for monochromatic X-ray imaging at 72.3°. The designed crystal produces excellent images of a laser-produced plasma emitting He-like Ti X-rays at 4.75 keV. Based on the simulations, the imaging resolutions of the spherical and toroidal crystals in the sagittal direction are found to be 15 and 5 μm, respectively. Moreover, the simulation results show that a higher resolution image of the source can be obtained by using a toroidal crystal. An X-ray backlight imaging experiment is conducted using 4.75 keV He-like Ti X-rays, a 3 × 3 metal grid, an imaging plate and a toroidal quartz crystal with a lattice constant of 2d = 0.2749 nm. The meridional and sagittal radii of the toroidal α-quartz crystal are 295.6 and 268.5 mm, respectively. A highly resolved image of the microgrid, with a spatial resolution of 10 μm, is obtained in the experiment. By using similar toroidal crystal designs, the application of a spatially resolved spectrometer with high-resolution X-ray imaging ability is capable of providing imaging data with the same magnification ratio in the sagittal and meridional planes.

Optimizing the energy bandwidth for transmission full-field X-ray microscopy experiments.

Full-field transmission X-ray microscopy (TXM) is a very potent high-resolution X-ray imaging technique. However, it is challenging to achieve fast acquisitions because of the limited efficiency of the optics. Using a broader energy bandwidth, for example using a multilayer monochromator, directly increases the flux in the experiment. The advantage of more counts needs to be weighed against a deterioration in achievable resolution because focusing optics show chromatic aberrations. This study presents theoretical considerations of how much the resolution is affected by an increase in bandwidth as well as measurements at different energy bandwidths (ΔE/E = 0.013%, 0.27%, 0.63%) and the impact on achievable resolution. It is shown that using a multilayer monochromator instead of a classical silicon double-crystal monochromator can increase the flux by an order of magnitude with only a limited effect on theresolution.

All-inorganic perovskite nanocrystals: next-generation scintillation materials for high-resolution X-ray imaging.

With super strong penetrability, high-energy X-rays can be applied to probe the inner structure of target objects under nondestructive situations. Scintillation materials can down-convert X-rays into visible light, enabling the reception of photon signals and photoelectric conversion by common sensing arrays such as photomultiplier tubes and amorphous-Si photodiode matrixes. All-inorganic perovskite nanocrystals are emerging photovoltaic and scintillation materials, with tremendous light-conversion efficiency and tunable luminous properties, exhibiting great potential for high-quality X-ray imaging. Recent advancements in nanotechnology further accelerate the performance improvement of scintillation materials. In this review, we will provide a comprehensive overview of novel all-inorganic perovskite nano-scintillators in terms of potential applications in low-dose X-ray medical radiography. Compared with conventional scintillators, the merits/drawbacks, challenges, and scintillation performance control will be the focus of this article.

3D virtual histopathology of cardiac tissue from Covid-19 patients based on phase-contrast X-ray tomography.

For the first time, we have used phase-contrast X-ray tomography to characterize the three-dimensional (3d) structure of cardiac tissue from patients who succumbed to Covid-19. By extending conventional histopathological examination by a third dimension, the delicate pathological changes of the vascular system of severe Covid-19 progressions can be analyzed, fully quantified and compared to other types of viral myocarditis and controls. To this end, cardiac samples with a cross-section of 3.5mm were scanned at a laboratory setup as well as at a parallel beam setup at a synchrotron radiation facility the synchrotron in a parallel beam configuration. The vascular network was segmented by a deep learning architecture suitable for 3d datasets (V-net), trained by sparse manual annotations. Pathological alterations of vessels, concerning the variation of diameters and the amount of small holes, were observed, indicative of elevated occurrence of intussusceptive angiogenesis, also confirmed by high-resolution cone beam X-ray tomography and scanning electron microscopy. Furthermore, we implemented a fully automated analysis of the tissue structure in the form of shape measures based on the structure tensor. The corresponding distributions show that the histopathology of Covid-19 differs from both influenza and typical coxsackie virus myocarditis.

Single-Crystalline Perovskite Nanowire Arrays for Stable X-ray Scintillators with Micrometer Spatial Resolution

X-ray scintillation detectors based on metal halide perovskites have shown excellent light yield, but they mostly target applications with spatial resolution at the tens of micrometers level. Here, we use a one-step solution method to grow arrays of 15-μm-long single-crystalline CsPbBr3 nanowires (NWs) in an AAO (anodized aluminum oxide) membrane template, with nanowire diameters ranging from 30 to 360 nm. The CsPbBr3 nanowires in AAO (CsPbBr3 NW/AAO) show increasing X-ray scintillation efficiency with decreasing nanowire diameter, with a maximum photon yield of ∼5 300 ph/MeV at 30 nm diameter. The CsPbBr3 NW/AAO composites also display high radiation resistance, with a scintillation-intensity decrease of only ∼20–30% after 24 h of X-ray exposure (integrated dose 162 Gyair) and almost no change after ambient storage for 2 months. X-ray images can distinguish line pairs with a spacing of 2 μm for all nanowire diameters, while slanted edge measurements show a spatial resolution of ∼160 lp/mm at modulation transfer function (MTF) = 0.1. The combination of high spatial resolution, radiation stability, and easy fabrication makes these CsPbBr3 NW/AAO scintillators a promising candidate for high-resolution X-ray imaging applications.

Micro- and Nano-Scales Three-Dimensional Characterisation of Softwood.

Understanding the mechanical response of cellular biological materials to environmental stimuli is of fundamental importance from an engineering perspective in composites. To provide a deep understanding of their behaviour, an exhaustive analytical and experimental protocol is required. Attention is focused on softwood but the approach can be applied to a range of cellular materials. This work presents a new non-invasive multi-scale approach for the investigation of the hygro-mechanical behaviour of softwood. At the TOMCAT beamline of the Paul Scherrer Institute, in Switzerland, the swelling behaviour of softwood was probed at the cellular and sub-cellular scales by means of 3D high-resolution phase-contrast X-ray imaging. At the cellular scale, new findings in the anisotropic and reversible swelling behaviour of softwood and in the origin of swelling hysteresis of porous materials are explained from a mechanical perspective. However, the mechanical and moisture properties of wood highly depend on sub-cellular features of the wood cell wall, such as bordered pits, yielding local deformations during a full hygroscopic loading protocol.