Flat-panel X-ray Source Research Articles

Cold Cathode Flat Panel X-ray Source for Talbot–Lau Grating Interferometer using Zinc Oxide Nanowire Field Emitter Arrays and Periodic Microstructured Anode

Cold Cathode Flat Panel X-ray Source for Talbot–Lau Grating Interferometer using Zinc Oxide Nanowire Field Emitter Arrays and Periodic Microstructured Anode

Two Monte Carlo-based simulators for imaging-system modeling and projection simulation of flat-panel X-ray source

Two Monte Carlo-based simulators for imaging-system modeling and projection simulation of flat-panel X-ray source

Feasibility Study of a Cold-Cathode Flat-Panel X-Ray Source With Microarray Anode Target for Grating Interferometer Computed Tomography

Feasibility Study of a Cold-Cathode Flat-Panel X-Ray Source With Microarray Anode Target for Grating Interferometer Computed Tomography

Transparent Flat Panel X-Ray Source Using ITO Transmission Anode and ZnO Nanowire Cold Cathode

X-ray sources have important applications in medical diagnosis, industrial inspection, etc. Transparent X-ray source has not been reported before, which enables the applications such as simultaneous imaging using X-ray and visible light. In this article, a fully vacuum-encapsulated transparent flat-panel X-ray source was prepared by using ZnO nanowires cold cathode and indium-tin-oxide (ITO) transmission anode. The effect of thicknesses of ITO film on X-ray radiation intensity was studied. A radiation dose rate of 6.85 mGy/s measured at 5 cm in front of the flat-panel X-ray source (FPXS) under 48-kV anode voltage and an optical transmittance of 72.63% at 550-nm light were achieved. X-ray spectra show the indium is the main element to generate the X-ray. By adopting the device in an X-ray and visible light dual-functional inspection set-up, the X-ray and visible light imaging of objects were demonstrated simultaneously.

Deep learning based de-overlapping correction of projections from a flat-panel micro array X-ray source: Simulation study

PurposeFlat-panel X-ray source is an experimental X-ray emitter with target application of static computer tomography (CT), which can save imaging space and time. However, the X-ray cone beams emitted by the densely arranged micro-ray sources are overlapped, causing serious structural overlapping and visual blur in the projection results. Traditional deoverlapping methods can hardly solve this problem well. MethodWe converted the overlapping cone beam projections to parallel beam projections through a U-like neural network and selected structural similarity (SSIM) loss as the loss function. In this study, we converted three kinds of overlapping cone beam projections of the Shepp–Logan, line-pairs, and abdominal data with two overlapping levels to corresponding parallel beam projections. Training completed, we tested the model using the test set data that was not used at the training phase, and evaluated the difference between the test set conversion results and their corresponding parallel beams through three indicators: mean squared error (MSE), peak signal-to-noise ratio (PSNR) and SSIM. In addition, projections from head phantoms were applied for generalization test. ResultIn the Shepp–Logan low-overlapping task, we obtained a MSE of 1.624×10-5, a PSNR of 47.892 dB, and a SSIM of 0.998 which are the best results of the six experiments. For the most challenging abdominal task, the MSE, PSNR, and SSIM are 1.563×10-3, 28.0586 dB, and 0.983, respectively. In more generalized data, the model also achieved good results. ConclusionThis study proves the feasibility of utilizing the end-to-end U-net for deblurring and deoverlapping in the flat-panel X-ray source domain.

Flat-panel Addressable Cold-cathode X-ray Source based Stationary CT Architecture

Flat-panel Addressable Cold-cathode X-ray Source based Stationary CT Architecture

Optimizing Performance of Coaxis Planar-Gated ZnO Nanowire Field-Emitter Arrays by Tuning Pixel Density.

Gated ZnO nanowire field emitter arrays (FEAs) have important applications in large-area vacuum microelectronic devices such as flat panel X-ray sources and photodetectors. As the application requires high-pixel-density FEAs, how the pixel density affects the emission performance of the gated ZnO nanowire FEAs needs investigating. In this paper, the performance of coaxis planar -gated ZnO nanowire FEAs was simulated under different pixel sizes while keeping the lateral geometric parameter in proportion. The variations in emission current and gate modulation with pixel size were obtained. Using the obtained device parameters, the coaxis planar-gated ZnO nanowire FEAs were prepared. Field emission measurement results showed that a current density of 3.2 mA/cm2 was achieved from the fabricated ZnO nanowire FEAs when the gate voltage was 140 V. A transconductance of 253 nS was obtained, indicating effective gate control. The improved performance is attributed to optimized gate modulation.

Pulsed voltage driving enhanced electron emission in ZnO nanowire cold cathode flat-panel X-ray source

A fully vacuum-sealed flat-panel X-ray source was fabricated composed of molybdenum metal anode and ZnO nanowire field emitters array cathode. The cathode current and X-ray radiation dose rate of the device were measured when the anode is applied with direct current (DC) and pulsed voltage, respectively. It is found that the peak emission current and corresponding dose rate under pulsed voltage driving are much higher than those under DC voltage driving. The phenomena may be explained by a plasma induced field emission enhancement related to the electron bombardment induced gas desorption. Clear projection X-ray imaging of moving objects was obtained using pulsed voltage driving. The result shows that owing to the enhanced emission current driven by the pulsed voltage, the flat-panel X-ray source can achieve fast and clear imaging of high-speed moving objects. Our results are of significance for the application of large area flat-panel X-ray source in dynamic imaging.

Fully Vacuum-Sealed Diode-Structure Addressable ZnO Nanowire Cold Cathode Flat-Panel X-ray Source: Fabrication and Imaging Application.

A fully vacuum-sealed addressable flat-panel X-ray source based on ZnO nanowire field emitter arrays (FEAs) was fabricated. The device has a diode structure composed of cathode panel and anode panel. ZnO nanowire cold cathodes were prepared on strip electrodes on a cathode panel and Mo thin film strips were prepared on an anode panel acting as the target. Localized X-ray emission was realized by cross-addressing of cathode and anode electrodes. A radiation dose rate of 10.8 μGy/s was recorded at the anode voltage of 32 kV. The X-ray imaging of objects using different addressing scheme was obtained and the imaging results were analyzed. The results demonstrated the feasibility of achieving addressable flat-panel X-ray source using diode-structure for advanced X-ray imaging.

Fully vacuum-sealed addressable nanowire cold cathode flat-panel x-ray source

Addressable flat-panel x-ray source has important applications in next-generation low-dose x-ray imaging technology. In this study, a fully vacuum-sealed addressable flat-panel x-ray source has been fabricated using a ZnO nanowire cold cathode. The x-ray source was formed by assembling gated ZnO nanowire field emitters and a molybdenum thin film transmission anode target. Pulsed and addressable x-ray emission was achieved by applying voltages to the extraction gate. Radiation dose rates of 235 nGy/s were achieved when the device was operated at 21 kV anode voltage and 140 V gate voltage. Projection x-ray images of objects were obtained by the flat-panel x-ray source. Our results demonstrated the feasibility of a fully addressable cold cathode flat-panel x-ray source.

High Current Field Emission from Large-Area Indium Doped ZnO Nanowire Field Emitter Arrays for Flat-Panel X-ray Source Application.

Large-area zinc oxide (ZnO) nanowire arrays have important applications in flat-panel X-ray sources and detectors. Doping is an effective way to enhance the emission current by changing the nanowire conductivity and the lattice structure. In this paper, large-area indium-doped ZnO nanowire arrays were prepared on indium-tin-oxide-coated glass substrates by the thermal oxidation method. Doping with indium concentrations up to 1 at% was achieved by directly oxidizing the In-Zn alloy thin film. The growth process was subsequently explained using a self-catalytic vapor-liquid-solid growth mechanism. The field emission measurements show that a high emission current of ~20 mA could be obtained from large-area In-doped sample with a 4.8 × 4.8 cm2 area. This high emission current was attributed to the high crystallinity and conductivity change induced by the indium dopants. Furthermore, the application of these In-doped ZnO nanowire arrays in a flat-panel X-ray source was realized and distinct X-ray imaging was demonstrated.

Diagonal 4-in ZnO Nanowire Cold Cathode Flat-Panel X-Ray Source: Preparation and Projection Imaging Properties

Uniform large-area flat-panel X-ray sources have potential applications in projection imaging. Achieving such a source has remained a challenge. A diagonal 4-in cold cathode flat-panel X-ray source device has been fabricated using ZnO nanowire field emitter arrays. A large-area uniform X-ray emission was produced, and projection imaging with a resolution of more than 5.0 lp/mm was realized. Its projection imaging resolution and its dependence on geometric imaging parameter settings were studied along with the imaging performance of the device. Simulations using the fast ray-tracing algorithm were performed, yielding results consistent with those from experiments. Optimal parameter settings for high-resolution projection imaging using the flat-panel X-ray source are presented. This study has significance in the application of this cold cathode flat-panel X-ray source in X-ray imaging.

A Novel Stationary CT Scheme Based on High-Density X-Ray Sources Device

With the introduction of cold electron sources such as nanotubes, X-ray sources became small in size so that many sources are installed in array to form stationary CT, which brings benefits of simplicity in mechanism and fast response. However, the nanotube-based X-ray source is still singly packaged and hence density of X-ray sources is limited, which introduces severe sparse-view artifacts and could not be used in practice. With the invention of X-ray sources device based on ZnO nanowires as cold electron emitters, a large amount of X-ray sources is first integrated in a flat panel device. In this study, we design a stationary CT architecture using high-density sources devices, called HD-SCT, and develop corresponding reconstruction algorithm. Specifically, several flat panel detectors and X-ray sources devices are spliced together to form a source-detector plate. Multiple source-detector plates are organized as a polygon that encloses object to complete CT scanning. In HD-SCT, X-ray sources are close to object which can significantly decrease CT device volume. The X-ray beam emitted by each source just cover part of object and the spot sources alternately light to completely scan object. Simultaneously, we propose a reconstruction method for the specific configuration which adopts an iterative algorithm to resolve the reconstruction based on alterative part projections, as well as a novel correction process of projection completion for the shadowed area of placing X-ray source devices. To validate the design of the proposed HD-SCT, we execute a series of simulation experiments, which show that the proposed HD-SCT and corresponding reconstruction method effectively remove the artifacts caused by the embed X-ray source device. The results also disclose that with the increase of density of X-ray sources, the resolution of reconstruction has been dramatically improved, which demonstrates the practical value of introducing high-density X-ray sources device into stationary CT design.

Defect-Enhanced Field Emission from WO3 Nanowires for Flat-Panel X-ray Sources

Achieving high current emission from one-dimensional nanowire (NW) field emitters is essential for their application as X-ray sources. In this study, field emission (FE) from tungsten trioxide NWs ...

Tungsten Target Optimization for Photon Fluence Maximization of a Transmission-Type Flat-Panel X-Ray Source by Monte Carlo Simulation and Experimental Measurement

The cold cathode flat-panel X-ray source is a new type of X-ray source with advantage of smaller footprint and lower-dose imaging than current sources. In this paper, we optimized the thickness of the anode target of a flat-panel X-ray source to maximize the photon fluence of X-rays generated from the device. Utilizing EGSnrc-based Monte Carlo code, X-ray fluence was calculate from the simulated photons deposited in the virtual detector. These results revealed an optimal target thickness at a specific anode voltage to maximize the output of X-ray intensity. For experimental validation, tungsten thin film anodes with different thicknesses were prepared, and a flat-panel X-ray source was fabricated using a ZnO nanowire cold cathode. A figure of merit was introduced to characterize the output efficiency of the X-rays. The experimental results agree well with the simulation results, showing an optimal tungsten-target thickness of 1200 nm at an anode voltage of 40 kV. Using a flat-panel X-ray source with the optimized anode thickness, we took X-ray absorption images of both biological and nonbiological subjects, and high-resolution images were demonstrated.

Investigation of the temperature dependent field emission from individual ZnO nanowires for evidence of field-induced hot electrons emission

ZnO nanowires as field emitters have important applications in flat panel display and x-ray source. Understanding the intrinsic field emission mechanism is crucial for further improving the performance of ZnO nanowire field emitters. In this article, the temperature dependent field emission from individual ZnO nanowires was investigated by an in situ measurement in ultra-high vacuum. The divergent temperature-dependent Fowler–Nordheim plots is found in the low field region. A field-induced hot electrons emission model, that takes into account penetration length, is proposed to explain the results. The carrier density and temperature dependence of the field-induced hot electrons emission current are derived theoretically. The obtained results are consistent with the experimental results, which could be attributed to the variation of effective electron temperature. All of these are important for a better understanding on the field emission process of semiconductor nanostructures.

A double-sided radiating flat-panel X-ray source using ZnO nanowire field emitters

A double-sided radiating flat-panel X-ray source device has been developed. The device has a diode configuration composed of an anode target of a tungsten thin film and field-emitter arrays of ZnO nanowires prepared on glass substrates. The X-ray radiation comes from both transmission and reflection of X-rays induced by electron bombardment. When operated at 24 kV with an anode current of 3.16 mA, radiation dose rates of ∼200 mGy/min and ∼210 mGy/min were recorded positioning at 4 cm away from the front and back sides of the vacuum-sealed flat-panel X-ray source, respectively. Clear X-ray images with high contrast were taken by the radiation from both sides of the device. The reported device has great potential in making compact X-ray radiography and irradiation systems.

Thermo-enhanced field emission from ZnO nanowires: Role of defects and application in a diode flat panel X-ray source

A thermo-enhanced field emission phenomenon was observed from ZnO nanowires. The field emission current increased by almost two orders of magnitude under a constant applied electric field, and the turn-on field decreased from 6.04MV/m to 5.0MV/m when the temperature increased from 323 to 723K. The Poole–Frenkel electron excitation from the defect-induced trapping centers to the conduction band under high electric fields is believed to be the primary cause of the observed phenomenon. The experimental results fit well with the proposed physical model. The field emission from ZnO nanowires with different defect concentrations further confirmed the role of defects. Using the thermo-enhanced field emission phenomenon, a diode flat panel X-ray source was demonstrated, for which the energy and dose can be separately tuned. The thermo-enhanced field emission phenomenon observed from ZnO nanowires could be an effective way to realize a large area flat panel multi-energy X-ray source.

Transmission type flat-panel X-ray source using ZnO nanowire field emitters

A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

Nitrogen incorporated ultrananocrystalline diamond based field emitter array for a flat-panel x-ray source

A field emission based flat-panel transmission x-ray source is being developed as an alternative for medical and industrial imaging. A field emitter array (FEA) prototype based on nitrogen incorporated ultrananocrystalline diamond film has been fabricated to be used as the electron source of this flat panel x-ray source. The FEA prototype was developed using conventional microfabrication techniques. The field emission characteristics of the FEA prototype were evaluated. Results indicated that emission current densities of the order of 6 mA/cm2 could be obtained at electric fields as low as 10 V/μm to 20 V/μm. During the prototype microfabrication process, issues such as delamination of the extraction gate and poor etching of the SiO2 insulating layer located between the emitters and the extraction layer were encountered. Consequently, alternative FEA designs were investigated. Experimental and simulation data from the first FEA prototype were compared and the results were used to evaluate the performance of alternative single and double gate designs that would yield better field emission characteristics compared to the first FEA prototype. The best simulation results are obtained for the double gate FEA design, when the diameter of the collimator gate is around 2.6 times the diameter of the extraction gate.