Nanofocus X-ray Source Research Articles

Laboratory x-ray nano-computed tomography for biomedical research

High-resolution x-ray tomography is a common technique for biomedical research using synchrotron sources. With advancements in laboratory x-ray sources, an increasing number of experiments can be performed in the lab. In this paper, the design, implementation, and verification of a laboratory setup for x-ray nano-computed tomography is presented using a nano-focus x-ray source and high geometric magnification not requiring any optical elements. Comparing a scintillator-based detector to a photon counting detector shows a clear benefit of using photon counting detectors for these applications, where the flux of the x-ray source is limited and samples have low contrast. Sample contrast is enhanced using propagation-based phase contrast. The resolution of the system is verified using 2D resolution charts and using Fourier Ring Correlation on reconstructed CT slices. Evaluating noise and contrast highlights the benefits of photon counting detectors and the contrast improvement through phase contrast. The implemented setup is capable of reaching sub-micron resolution and satisfying contrast in biological samples, like paraffin embedded tissue.

Development of projection X-ray microscope with 100 nm spot size

ABSTRACT A projection X-ray microscope useful for industrial non-destructive inspections and various biological observations has been developed. By installing a Schottky type electron source, a nano focus X-ray source with 100 nm focal spot size that is easy to handle in various laboratories is successfully achieved at 20 to 80 kVp. An imaging system has been composed of a vertical type that can adjust a sample position on the optical axis, and high-resolution imaging can be achieved by using a high precision stage unit. A test chart with 200 nm line width can be clearly confirmed by a transmission image, and CT images with high spatial resolution were also obtained for a test sample of glass containing air micro-bubbles. Finally, we confirmed that the spatial resolution of the system estimated from the obtained CT images does not contradict the result of the evaluation formula of spatial resolution including the effect of X-rays diffraction.

Contrast based method for the automated analysis of transfer functions and spatial resolution limits of micro- and nano-focus computed tomography systems: Evaluation with simulated data

Micro- and nano-focus X-ray sources are extensively used in X-ray computed tomography systems to achieve high spatial resolution. This is essential, when scanning small objects, where resolution limitations are mainly connected to the size of the focal spot. Therefore, much effort has been put into reducing the size of the focal spot, where the measurement of the focal spot size is challenging. In this paper, the implementation of a new evaluation method for the quantitative determination of the system’s transfer function and the source’ spot size and shape are presented. The spatial resolution is calculated at different evaluation points to assess which particular threshold should be used to obtain the resolution limit and the focal spot size and shape. The implementation is explained and evaluated with the aid of simulated and real radiographs of the test chart, featuring line and star patterns designed to bridge the gap between existing resolution standards.

Development of Projection X-ray Microscope with 100 nm Spot Size

A projection X-ray microscope useful for industrial non-destructive inspections and various biological observations has been developed. By installing a Schottky type electron source, a nano focus X-ray source with 100 nm focal spot size that is easy to handle in various laboratories is successfully achieved at 20 to 80 kVp. An imaging system has been composed of a vertical type that can adjust a sample position on the optical axis, and high-resolution imaging can be achieved by using a high precision stage unit. A test chart with 200 nm line width can be clearly confirmed by a transmission image, and CT images with high spatial resolution were also obtained for a test sample of glass containing air micro-bubbles. Finally, we confirmed that the spatial resolution of the obtained CT images does not contradict the measurement conditions by using the evaluation formula of spatial resolution including the effect of X-rays diffraction.

Lenseless X-ray nano-tomography down to 150 nm resolution: on the quantification of modulation transfer and focal spot of the lab-based ntCT system

The ntCT nano tomography system is a geometrically magnifying X-ray microscopy system integrating the recent Excillum NanoTube nano-focus X-ray source and a CdTe photon counting detector from Dectris. The system's modulation transfer function (MTF) and corresponding point spread function (PSF) are characterized by analyzing the contrast visibility of periodic structures of a star pattern featuring line width from 150 nm to 1.5 μm. The results, which can be attributed to the characteristics of the source spot, are crosschecked by scanning the source's electron focus over an edge of the structured transmission target in order to obtain an independent measurement of its point spread function. For frequencies above 1000 linepairs/mm, the MTF is found to correspond to a Gaussian PSF of 250 nm full width at half maximum (FWHM) . The lower frequency range down to 340 linepairs/mm shows an additional Gaussian contribution of 1 μm FWHM . The resulting resolution ranges at 3200 linepairs/mm, which is consistent with the visual detectability of the smallest 150 nm structures within the imaged star pattern.

High-resolution Imaging by Using Liquid MetalJet Microfocus and Nano-focus X-ray Sources

High-resolution Imaging by Using Liquid MetalJet Microfocus and Nano-focus X-ray Sources

High-resolution Nano-imaging with Transmission Nanofocus X-ray Source

High-resolution Nano-imaging with Transmission Nanofocus X-ray Source

High beam-current density of a 10-keV nano-focus X-ray source

Abstract The electron beam-current density at a target greatly affects imaging intensity and contrast when using a low-energy nano-focus X-ray source. This paper proposes a new electron gun comprising a 10-keV nano-focus X-ray source with a single-pole magnetic lens to improve its effective brightness and beam-current density. After analyzing the effect of the electric field on the extended Schottky emission, we first optimized the anode with high effective brightness and a fine virtual spot with enough intensity for nano-focus X-ray imaging. High effective beam-current density was then obtained by optimizing the position, geometry and electrical supplies of the single-pole magnetic lens. The effective brightness of this electron gun is 1.70 × 108 A•cm−2•sr−1, and the nano-focus X-ray source has a spot size of 41 nm when its tube current is 2 μ A. This electron gun achieves higher beam current density (1.6 × 105A•cm−2), and its collimated landing beam efficiently transports the beam current in the X-ray source.

A Fully Closed Nano-Focus X-Ray Source With Carbon Nanotube Field Emitters

We developed a fully closed nano-focus X-ray source using carbon nanotube (CNT) field emitters. The nano-focus X-ray source includes a fully vacuum-sealed CNT Electron-gun (E-gun) tube and E-beam-focusing modules consisting of electrostatic and magnetic lenses, facilitating very compact and high-resolution X-ray imaging. The paste-printed CNT emitters were prepared in a small pattern as an electron source, and the entire components, including the CNT emitter module, Cu tubes, collimators, and transmissive anode target, were specially brazed at an elevated temperature, resulting in a very compact E-gun tube. The CNT emitter showed a stable and reliable emission current with its density of over 300 mA/cm2 even in the vacuum-sealed E-gun tube. With the anode grounded and the CNT emitter module biased to negative high voltages, we achieved a considerably magnified x-ray image of a several hundred nanometer resolution. The fully vacuum-sealed CNT E-gun tube along with the magnetic lens module can offer much more compact, easily maintainable, high-resolution X-ray imaging compared with conventional open-type thermionic X-ray sources.

Implementation of a Computed Tomography System based on a laboratory-based nanofocus X-ray source.

Implementation of a Computed Tomography System based on a laboratory-based nanofocus X-ray source.

X-ray imaging with sub-micron resolution using large-area photon counting detectors Timepix

As X-ray micro-CT became a popular tool for scientific purposes a number of commercially available CT systems have emerged on the market. Micro-CT systems have, therefore, become widely accessible and the number of research laboratories using them constantly increases. However, even when CT scans with spatial resolution of several micrometers can be performed routinely, data acquisition with sub-micron precision remains a complicated task. Issues come mostly from prolongation of the scan time inevitably connected with the use of nano-focus X-ray sources. Long exposure time increases the noise level in the CT projections. Furthermore, considering the sub-micron resolution even effects like source-spot drift, rotation stage wobble or thermal expansion become significant and can negatively affect the data. The use of dark-current free photon counting detectors as X-ray cameras for such applications can limit the issue of increased image noise in the data, however the mechanical stability of the whole system still remains a problem and has to be considered. In this work we evaluate the performance of a micro-CT system equipped with nano-focus X-ray tube and a large area photon counting detector Timepix for scans with effective pixel size bellow one micrometer.

Myoanatomy of the velvet worm leg revealed by laboratory-based nanofocus X-ray source tomography

X-ray computed tomography (CT) is a powerful noninvasive technique for investigating the inner structure of objects and organisms. However, the resolution of laboratory CT systems is typically limited to the micrometer range. In this paper, we present a table-top nanoCT system in conjunction with standard processing tools that is able to routinely reach resolutions down to 100 nm without using X-ray optics. We demonstrate its potential for biological investigations by imaging a walking appendage of Euperipatoides rowelli, a representative of Onychophora-an invertebrate group pivotal for understanding animal evolution. Comparative analyses proved that the nanoCT can depict the external morphology of the limb with an image quality similar to scanning electron microscopy, while simultaneously visualizing internal muscular structures at higher resolutions than confocal laser scanning microscopy. The obtained nanoCT data revealed hitherto unknown aspects of the onychophoran limb musculature, enabling the 3D reconstruction of individual muscle fibers, which was previously impossible using any laboratory-based imaging technique.

Influences on 3D image quality in a high-resolution Xray laminography system

Recently, we demonstrated that projective X-ray microscopy is feasible with a two-dimensional spatial resolution down to 100 nm by using laboratory nanofocus X-ray sources and a geometric magnification of up to 1000x. Based on these previous results, we developed a high-resolution X-ray laminography system which uses an optimized thin-film X-ray transmission target together with a modified electron probe micro analyzer. Unlike conventional axial computed tomography (CT), 3D laminography imaging involves a linear translation of both detector and object with respect to a stationary point source.In this contribution we present a detailed characterization of the setup concerning especially the laminographic imaging mode. The quality of the volume reconstruction is assessed by simulating an ideal setup with an analytical model including features down to 200 nm which are resolved in the setup given a high enough SNR in the projections.We further address the issue of a drop in the detector resolution under oblique X-ray illumination which is a common problem to such systems. The finite penetration depth of the X-rays into the detector pixels causes an anisotropic blurring of the detector point spread function (PSF) under oblique irradiation. We tested the influence of this blurring by calculating the illumination-dependent modulation transfer function (MTF) of the detector. Our measurements are supported by numerical simulations of the detector MTF. Both simulations and measurements show a drop in spatial resolution (20% of the MTF) from 12.5 lp/mm (irradiation perpendicular to the detector screen) down to 5.2 lp/mm (irradiation 30° oblique to the screen).Furthermore, first examples of 3D imaging of test structures and material imaging are given.

Characterization of superconducting wires and cables by X-ray micro-tomography

Due to their mechanical strength and ability to withstand the large electromagnetic force applied to the superconductors in large magnets during excitation, the Cable-in-Conduit-Conductor (CICC) type superconductors will be employed in the next stage of fusion magnets. Here, we discuss the recent results on the application of a non-invasive method for the characterization of CCIC by X-ray micro-tomography (μXCT). The experiments have been carried out on a high resolution X-ray tomograph in INFLPR (http://tomography.inflpr.ro). An open type nanofocus X-ray source with maximum high voltage of 225kVp at 15–30W maximum power and multiple targets of W on different windows materials (Be, Al, Cu or diamond) is the main component. X-rays are detected by means of amorphous silicon flat panel sensor in the cone-beam configuration and high-energy efficient line sensor based on individual scintillators in the fan-beam scanning configuration. The quality of tomographic images (≈40μm space resolution) allowed the majority of strands of analyzed CICC samples to be fully reconstructed along the investigated segment (up to 300mm long). Our method provides: (i) local and global void fractions (over a 300mm length of the sample), (ii) void homogeneity factor as the ratio between void space surface and perimeter and (iii) twist pitch angle of individual strands and its distribution in 3D. It can be used to investigate superconducting CICC during their manufacture, installation or after service inspection, for purposes of QA, characterization or development.

Laboratory X-ray microscopy with a nano-focus X-ray source

In this paper we describe the optimization of transmission X-ray targets by Monte-Carlo simulation for a laboratory X-ray microscopy setup. We identified two optimal target layer thicknesses (0.1 μm and 0.7 μm) for a high-resolution target and a high-flux target. Measurements show a decrease in focal spot size by one third or an increase in X-ray flux by a factor of three compared to those of a standard micro-focus target. Focal spot sizes down to 154 nm and 260 nm are achievable with the optimized targets. Simulation results for the X-ray flux match well to the experimental results, whereas the results for the focal spot sizes still show discrepancies attributed to the simplified simulation setup.

X-ray phase contrast imaging using single absorption coded aperture

A new method for X-ray phase contrast imaging is proposed in which only one absorption grating (acting in fact as a coded aperture) and a table-top nano-focus X-ray source are used. This method is based on very precise determination of position of the projected pattern downstreaming from the aperture with and without the inspected object directly from the image of the pattern. The technique is successfully demonstrated on the table-top setup equipped with Medipix family detectors and a nano-focus X-ray source (source-to-detector distance <1 m).

Towards sub-100-nm X-ray microscopy for tomographic applications

We have demonstrated that structures down to 150 nm can be visualized in X-ray projection images using nanofocus X-ray sources. Due to their unlimited depth of focus, they do not possess a limit on the specimen size. This is essential for three-dimensional tomographic imaging of samples with a diameter larger than a few microns. Further simulation studies have shown that optimization of the detector response curve and switching from a reflective X-ray target to a transmission target should allow us to reach sub-100-nm resolutions.

Characterisation of spectral performance of pixellated X-ray imaging detectors in a microscopy setup

In order to achieve energy resolved X-ray imaging with small pixel resolution, physical processes in the detector material such as fluorescence and charge sharing must be considered. This paper presents characterisation measurements performed with an X-ray microscopy setup for energy resolved imaging. The microscopy setup consists of a nanofocus X-ray source capable of 160 kV anode voltage, ESRF-type collimating slits and Medipix2 detectors. The detector systems developed in the Medipix collaboration are capable of energy resolved imaging. The measurements were performed by scanning an energy window through the spectrum. In this paper we have considered detectors made of Si, GaAs and CdTe for use in the microscopy setup. Both measurements and theoretical simulations are considered. For high X-ray energies, it is essential to consider fluorescence from the shielding and Compton scattering in silicon detectors.