Microfocus X-ray Tube Research Articles

Laboratory-based 3D X-ray standing-wave analysis of nanometre-scale gratings.

The increasing structural complexity and downscaling of modern nanodevices require continuous development of structural characterization techniques that support R&D and manufacturing processes. This work explores the capability of laboratory characterization of periodic planar nanostructures using 3D X-ray standing waves as a promising method for reconstructing atomic profiles of planar nanostructures. The non-destructive nature of this metrology technique makes it highly versatile and particularly suitable for studying various types of samples. Moreover, it eliminates the need for additional sample preparation before use and can achieve sub-nanometre reconstruction resolution using widely available laboratory setups, as demonstrated on a diffractometer equipped with a microfocus X-ray tube with a copper anode.

Speckle tracking phase-contrast computed tomography at an inverse Compton X-ray source.

Speckle-based X-ray imaging (SBI) is a phase-contrast method developed at and for highly coherent X-ray sources, such as synchrotrons, to increase the contrast of weakly absorbing objects. Consequently, it complements the conventional attenuation-based X-ray imaging. Meanwhile, attempts to establish SBI at less coherent laboratory sources have been performed, ranging from liquid metal-jet X-ray sources to microfocus X-ray tubes. However, their lack of coherence results in interference fringes not being resolved. Therefore, algorithms were developed which neglect the interference effects. Here, we demonstrate phase-contrast computed tomography employing SBI in a laboratory-setting with an inverse Compton X-ray source. In this context, we investigate and compare also the performance of the at synchrotron conventionally used phase-retrieval algorithms for SBI, unified modulated pattern analysis (UMPA) with a phase-retrieval method developed for low coherence systems (LCS). We successfully retrieve a full computed tomography in a phantom as well as in biological specimens, such as larvae of the greater wax moth (Galleria mellonella), a model system for studies of pathogens and infections. In this context, we additionally demonstrate quantitative phase-contrast computed tomography using SBI at a low coherent set-up.

Contrast-based notch-to-crack transfer function for digital radiography

To simulate cracks, a series of slits with depths ranging from 17.2% to 40% of 301 stainless steel (SS) plate thickness are fabricated for this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 75 ??m pixel pitch. The basis of this study is to determine the effect of detector scintillator blur, noise and pixelation on the contrast of the resultant radiographic image and, ultimately, on the detectability of a crack. Many crack detectability studies are performed on notched plates rather than true cracks. As the notch width becomes smaller than a pixel, the grey value of the image it generates will be averaged over the entire footprint of the pixel. Therefore, the contrast with neighbouring (no notch) pixels is reduced. This study develops a relationship between the material property, detector parameters, notch geometry and expected contrast that would result from the radiograph image. This relationship can be used as a transfer function towards evaluating the resultant contrast from a notch and extrapolating the results towards a hairline crack.

Spectral micro-CT for simultaneous gold and iodine detection, and multi-material identification

Multiple energy bin spectral micro-CT (SμCT) is an advanced imaging technique that allows multi-material decomposition according to their specific absorption patterns at a sub-100 μm scale. Typically, iodine is the preferred CT contrast agent for cardiovascular imaging, while gold nanoparticles have gained attention in recent years owing to their high absorption properties, biocompatibility and ability to target tumors.In this work, we demonstrate the potential for multi-material decomposition through SμCT imaging of a test sample at the PEPI lab of INFN Trieste. The sample, consisting of gold, iodine, calcium, and water, was imaged using a Pixirad1/PixieIII chromatic detector with multiple energy thresholds and a wide spectrum (100 kV) produced by a micro-focus X-ray tube. The results demonstrate the simultaneous detection and separation of the four materials at a spatial scale of 35 μm, suggesting the potential of this technique in improving material detectability and quantification in a range of pre-clinical applications, including cardiovascular and oncologic imaging.

Study of the Dynamics of Heating Anode Units in a Maskless Nanolithograph Based on an Array of Microfocus X-Ray Tubes

Study of the Dynamics of Heating Anode Units in a Maskless Nanolithograph Based on an Array of Microfocus X-Ray Tubes

Detector-trigger-based cardiac multiphase micro-CT imaging for small animals.

Micro-computed tomography is important in cardiac imaging for preclinical small animal models, but motion artifacts may appear due to the rapid heart rates. To avoid influence of motion artifacts, the prospective ECG gating schemes based on an X-ray source trigger have been investigated. However, due to the lack of pulsed X-ray exposure modes, high-resolution micro-focus X-ray sources do not support source triggering in most cases. To develop a fast-cardiac multiphase acquisition strategy using prospective ECG gating for micro-focus X-ray tubes with a continuous emission mode. The proposed detector-trigger-based prospective ECG gating acquisition scheme (DTB-PG) triggers the X-ray detector at the R peak of ECG, and then collects multiple phase projections of the heart in one ECG cycle by sequence acquisition. Cardiac multiphase images are reconstructed after performing the same acquisition in all views. The feasibility of this strategy was verified in multiphase imaging experiments of a phantom with 150 ms motion period and a mouse heart on a micro-focus micro-CT system with continuous emission mode. Using a high frame-rate CMOS detector, DTB-PG discriminates the positions of the motion phantom well in 10 different phases and enables to distinguish the changes in the cardiac volume of the mouse in different phases. The acquisition rate of DTB-PG is much faster than other prospective gating schemes as demonstrated by theoretical analysis. DTB-PG combines the advantages of prospective ECG gating strategies and X-ray detector-trigger mode to suppress motion artifacts, achieve ultra-fast acquisition rates, and relax hardware limitations.

A digital radiography study of the detectability of simulated cracks in 301 stainless steel

A series of simulated cracks in 301 stainless steel (SS), consisting of slits with depths from 12.8% to 40% of the plate thickness, is fabricated in this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 0.075 mm pixels at three angles of incidence (0°, 5° and 10°). The basis of the methodology for the minimum detectable slit width stems from the noise statistics in the images and a minimum detectable contrast-to-noise ratio (CNR) of 3. These minimum detectable widths range from 0.019 mm to 0.003 mm for 12.8%-deep and 40.0%-deep slits, respectively, for the 0° incidence condition. As the incident angle increases to 10°, the size of the minimum detectable slit width also increases, up to a factor of two for the shallower slits. It is noted that these simulated cracks, which have straight parallel sides and flat bottoms, do not accurately represent natural cracks that have irregular paths and taper at depth. Therefore, the results in this study represent the best scenario for detection, establishing some bounds of crack width detectability.

Artifacts reduction in high-acutance phase images for X-ray grating interferometry.

X-ray grating-based techniques often lead to artifacts in the phase retrieval process of phase objects presenting very fast spatial transitions or sudden jumps, especially in the field of non-destructive testing and evaluation. In this paper, we present a method that prevents the emergence of artifacts by building an interferogram corrected from any variations of the object intensity and given as input in the phase retrieval process. For illustration, this method is applied to a carbon fiber specimen imaged by a microfocus X-ray tube and a single 2D grating. A significant reduction of artifacts has been obtained, by a factor higher than 10. This evaluation has been performed experimentally thanks to the Confidence Map tool, a recently developed method that estimates the error distribution from the phase gradient information.

Industrial Computed Tomography Technique Development for Industrial Volumetric X-Ray CT

It is often stated that no two engineers will set up an industrial X-ray computed tomography (CT) scan with the same parameters. In this article, an orderly set of steps is presented that will lead to an acceptable CT scan result for typical cone beam (volumetric) systems with application to denser and/or larger objects. This approach can be applied when using minifocus, mesofocus, and microfocus X-ray tubes. The strategy covers preparation and general considerations, selection of the proper tube and detector, methods to determine the proper magnification, setting X-ray tube and detector parameters, considerations to achieve good image quality, and common mistakes to avoid.

X-ray phase contrast imaging model: application on tomography with a single 2D phase grating

In this paper, we propose a model dedicated to X-ray phase contrast imaging, which is well adapted to the characterization or inspection of low attenuating samples. We introduce a hybrid approach that combines a ray-tracing step with a wave propagation computation. The mathematical basis of our model is described and we present a comparison of the model to experimental results, for the case of an optical fiber sample, in the framework of a free-propagation phase technique. The extension to the 3D imaging is proposed on simulated data using a grating based technique or more precisely, a multilateral shearing interferometry. This technique uses a single 2D phase grating, which has the advantage of a simpler experimental setup and can be coupled with a standard micro-focus X-ray tube and a high-resolution detector. Our phase model was implemented on the CIVA CT simulation platform and used to generate easily different sets of projection data for any type of sample. While the method for 3D reconstruction has the same basis as the classical CT, we focus mainly on the intermediate processing steps, which are required for the phase retrieval and present the results for a phantom composed of spherical objects in different materials.

X-ray scintillator lens-coupled with CMOS camera for pre-clinical cardiac vascular imaging-A feasibility study.

We present the design and characterization of an X-ray imaging system consisting of an off-the-shelf CMOS sensor optically coupled to a CsI scintillator. The camera can perform both high-resolution and functional cardiac imaging. High-resolution 3D imaging requires microfocus X-ray tubes and expensive detectors, while pre-clinical functional cardiac imaging requires high flux pulsed (clinical) X-ray tubes and high-end cameras. Our work describes an X-ray camera, namely an “optically coupled X-ray(OCX) detector,” used for both the aforementioned applications with no change in the specifications. We constructed the imaging detector with two different CMOS optical imaging cameras called CMOS sensors, 1.A monochrome CMOS sensor coupled with an f1.4 lens and 2.an RGB CMOS sensor coupled with an f0.95 prime lens. The imaging system consisted of our X-ray camera, micro-focus X-ray source (50kVp and 1mA), and a rotary stage controlled from a personal computer (PC) and LabVIEW interface. The detective quantum efficiency (DQE) of the imaging system(monochrome) estimated using a cascaded linear model was 17% at 10 lp/mm. The system modulation transfer function (MTF) and the noise power spectrum (NPS) were inputs to the DQE estimation. Because of the RGB camera’s low quantum efficiency (QE), the OCX detector DQE was 19% at 5 lp/mm. The contrast to noise ratio (CNR) at different frame rates was studied using the capillary tubes filled with various dilutions of iodinated contrast agents. In-vivo cardiac angiography demonstrated that blood vessels of the order of 100 microns or above were visible at 40 frames per second despite the low X-ray flux. For high-resolution 3D imaging, the system was characterized by imaging a cylindrical micro-CT contrast phantom and comparing it against images from a commercial scanner.

Confidence map tool for gradient-based X-ray phase contrast imaging.

We present a graphical tool that we call a "confidence map". It allows to evaluate locally the quality of a phase image retrieved from the measurement of its gradients. The tool is primarily used to alert the observer to the presence of artifacts that could affect his interpretation of the image. It can also be used to optimize a phase imager since it associates a cause with the creation of each artifact: dislocation, under-sampling and noise. An illustration of the use of the confidence map tool is presented, based on a microfocus X-ray tube using multilateral shearing interferometry, a gradient based phase contrast technique employing a single 2D-grating.

Study of the dynamics of heating anode units in a maskless nanolithograph based on an array of microfocus X-ray tubes

In this paper, we study the dynamics of heating the matrix of anode nodes membrane with a transmission-type target under the action of a field emission current generated in the electronic system of a maskless X-ray nanolithograph. The promising membrane materials that provide the most efficient heat removal from the matrix have been determined, among which diamond-like films have shown the best thermal stability. At the calculated power of soft X-ray radiation P_X=2.5 nW, scattered by a pixel with a size of 20 nm and an X-ray resist irradiation dose D=100 J/m2, the exposure time was 25 μs. It is shown that during the exposure of a 150 mm plate, a diamond-like anode membrane with a size of 300x300 elements heats up from 20 to 62oC, which is 15-25 times lower than the heating temperature of alternative anode materials (Cu, Fe, Ni, Si, Al). The technological route for the fabrication of the matrix of anode nodes is described, taking into account the proposed methods for optimizing its design, aimed at reducing the thermal effects of heating during X-ray nanolithography processes. The results obtained can be applied in the development of a thermostable system of microfocus X-ray tubes as part of a maskless X-ray nanolithograph. Keywords: X-ray nanolithography, microfocus X-ray tube, transmission-type target, matrix of anode nodes, electron bombardment heating, thermal expansion, Bosch-process.

Microfocus X-ray Tubes

Introduction. X-ray inspection plays a unique role among all nondestructive testing methods for products and materials due to sufficiently high resolution and high penetrability. The present study is designed to consider the key features of microfocus X-ray sources, their areas of application, and main technical characteristics.Aim. The paper aims to systematize information and review modern X-ray radiation sources for the implementation of microfocus radiography.Materials and methods. The main designs of microfocus X-ray tubes (soldered and demountable) were considered relying on the experience of the St Petersburg State Electrotechnical University in developing and operating such equipment, as well as the experience and open-access publications of foreign researchers and developers. Data collected by leading research teams over the last ten years were analyzed.Results. The paper presents design features for each main type of microfocus X-ray tubes – soldered and demountable. All key structural elements are considered: an anode assembly, a cathode assembly, and a focusing system. The influence of anode target material on the X-ray tube radiation spectrum is shown. An original design of a liquid-anode microfocus X-ray tube is described to demonstrate its key features and advantages. In addition, the paper gives an overview of cathodes used in microfocus X-ray tubes (tungsten cathode and lanthanum hexaboride cathode), as well as providing a detailed description of calculations performed for focusing systems. Finally, the designs of modern X-ray tubes are presented.Conclusion. Modern X-ray tubes are high-tech products that allow for high-resolution research of various objects. The main advantage of testing performed with the use of X-ray tubes consists in high resolution (micron and submicron). The X-ray images of test objects used to determine their spatial resolution are given, which clearly illustrate the vast possibilities of this technology. In addition, ways to improve microfocus X-ray tubes are briefly discussed. The considered materials can be useful in selecting a nondestructive testing tool, as well as in developing and creating X-ray systems on the basis of microfocus X-ray tubes.

MODEL OF VOLUMETRIC HEAT SOURCES IN ANODE OF MICROFOCUS X-RAY TUBE

The work is developed a numerical-analytical approach to modeling thermal processes in a composite anode of microfocus X-ray tubes. At the first stage of modeling, with the help of well-known analytical approximations, the distribution function of volumetric heat sources is built. At the second stage, this function is used when solving a stationary boundary value problem with the Poisson equation by the Finite Elements Method. Using the proposed technique, an adequate assessment of the maximum power of the tube with the transmission type W-Be anode was developed.

Determination of trace Cr, Ni, Hg, As, and Pb in the tipping paper and filters of cigarettes by monochromatic wavelength X-ray fluorescence spectrometry

An analytical method is proposed to determine trace heavy metals chromium, nickel, mercury, arsenic, and lead in tipping paper and As and Pb in cigarette filters using monochromatic wavelength X-ray fluorescence spectrometry. It is very difficult to determine trace heavy metals by traditional energy-dispersive X-ray fluorescence spectrometry because of its high noise and low peak area. A MWXRF spectrometer was assembled with a LiF(420) double curved crystal and microfocal X-ray tube. High count X-ray was simultaneously generated and focused by LiF(420) DCC. With pressing pretreatment, the signal to background ratio was significantly improved. There was a good linear relation between the intensity by MWXRF and heavy metal content by ICP-MS and AAS. The limits of detection of the heavy elements were lower than 1.0 μg/g. A batch of cigarette tipping papers and filters were analyzed, there were only few heavy metals with low contents in the tipping paper and filters.

DEVELOPMENT OF HIGH POWER MICROFOCUS X-RAY TUBE

In this paper, we propose and study a new method for increasing the power of a microfocus X-ray tube of transmission type. The proposed method is based on the idea of using a heat pipe as a tube anode. A theoretical expression is obtained for the maximum power dissipated at such an anode, depending on the diameter of the electron beam and the thickness of the tungsten target. It is shown that the power of the proposed tube can be many times higher than the power of tubes with standard composite anodes. An electron-optical scheme of a tube with electrostatic focusing is proposed and analyzed.

X-Ray Phase-Contrast Image Reconstruction Based on the Chambolle-Pock Algorithm

The X-ray in-line phase-contrast imaging technique requires that the light source provides a spatially coherent X-ray beam typically generated by a microfocus X-ray tube in most laboratories. However, its small focal spot limits the lightness. An arrayed X-ray point source can overcome this drawback and provide an adequately bright spatial coherent light. However, the arrayed source will introduce artefacts to the phase-contrast image due to the point source spatial distribution. To eliminate these artefacts, an optimization-based algorithm is used to reconstruct the image as an optimization problem. An iterative method was developed to numerically solve the optimization problem by using the first-order primal-dual algorithm. The simulations demonstrate its convergence and reconstruction accuracy.

Radiological characteristics of endodontic materials and fragments of broken instruments in the canals of extracted teeth according to computed tomography

Microfocus cone-beam computed tomography (micro-CBCT) combines the technology of cone beam-computed tomography (CBCT) with a microfocus X-ray tube. Micro-CBCT is used in medicine in a relatively small number of experimental scientific works, the results of which demonstrate that micro-CBCT is a promising new diagnostic technique. The purpose of this work is a comparative analysis of the results of CBCT and micro-CBCT studies of the roots of extracted teeth before and after endodontic treatment, identification of the radiological characteristics of endodontic materials. Materials and methods. Devices Kavo OP 3D Vision (USA) and “Micron” (Russia) were used in order to scan 136 untreated and 91 endodontically treated roots of extracted teeth. A comparative analysis of the acquired CBCT and micro-CBCT reconstructions was performed. Results and discussion. Additional canals in the apexes of the roots, contents of the root canals and longitudinal fractures of the roots were imperceptible on the CBCT images of the untreated roots, but could be discovered with the help of micro-CBCT. The radiological characteristics of calcium-aluminosilicate cement, gutta-percha pins for lateral condensation of cold gutta-percha, zinc oxide-eugenol sealer, thermoplasticized gutta-percha on a plastic carrier, and epoxy resin-based sealer were determined for both of the computed tomography techniques. The microscopic structure of the materials could only be observed using the micro-CBCT reconstructions. A comparative analysis of the CBCT and micro-CBCT scans of the roots which contained intentionally broken metal instruments was performed. The presence of metal fragments resulted in stronger distortions on CBCT images compared to the results of micro-CBCT. Conclusion. Compared to CBCT, micro-CBCT is characterized by a higher spatial resolution and clarity of images, less pronounced artifacts from metal, allows to detect additional root canals, fracture lines and inclusions in root canals, makes it possible to characterize the structure of filling materials at the microscopic level.

Quantitative phase retrieval with low photon counts using an energy resolving quantum detector.

X-ray phase contrast imaging (PCI) combined with phase retrieval has the potential to improve soft-material visibility and discrimination. This work examined the accuracy, image quality gains, and robustness of a spectral phase retrieval method proposed by our group. Spectroscopic PCI measurements of a physical phantom were obtained using state-of-the-art photon-counting detectors in combination with a polychromatic x-ray source. The phantom consisted of four poorly attenuating materials. Excellent accuracy was demonstrated in simultaneously retrieving the complete refractive properties (photoelectric absorption, attenuation, and phase) of these materials. Approximately 10 times higher SNR was achieved in retrieved images compared to the original PCI intensity image. These gains are also shown to be robust against increasing quantum noise, even for acquisition times as low as 1 s with a low-flux microfocus x-ray tube (average counts of 250 photons/pixels). We expect that this spectral phase retrieval method, adaptable to several PCI geometries, will allow significant dose reduction and improved material discrimination in clinical and industrial x-ray imaging applications.