Large-area X-ray Imaging Research Articles

Heating revival of Cs3MnBr5 for anti-counterfeiting and large-area flexible X-ray imaging

Cesium manganese bromide metal halide has great potential in the field of X-ray imaging and anti-counterfeiting due to its excellent optoelectronic properties. Here, Cs3MnBr5 was successfully prepared by a simple method. Uniquely a novel phenomenon based on H2O induced color change was discovered, Cs3MnBr5 can recover from aqueous solution more than 10 times under heating, which can be used in fluorescent anti-counterfeiting applications. Furthermore, Cs3MnBr5@PDMS, prepared by the PDMS composite strategy, has been demonstrated to exhibit a stability that is 20 times greater than that of Cs3MnBr5. Simultaneously, the light yield of Cs3MnBr5 is evaluated to be 21688 photons/MeV. Furthermore, it has been successfully applied in non-destructive detection and biological imaging and the spatial resolution can be restored to 10 lp mm−1.

X-ray excited broadband blue emitting Lu2(1-x)Bi2xO3-PMMA thin films for high resolution imaging

In this paper, cubic-phase Lu2O3:Bi3+ nanoparticles, with a range of sizes between 110 and 180 nm, were obtained by a combination of co-precipitation and thermal annealing techniques. For these nanoparticles upon UV or X-ray excitation, strong broadband emission peaks at 410 and 480 nm corresponding to Bi3+ occupying S6 and C2 (Lu3+(S6) and Lu3+(C2)) sites, respectively, can be observed. On the basis of the concentration-dependent luminescence intensity ratios (I480(C2)/I410(S6)) of Bi3+(C2) to Bi3+(S6), the energy transfer from Bi3+(S6) to Bi3+(C2) can be confirmed at high Bi3+ concentration. In particular, their X-ray absorption coefficient, emission wavelength, afterglow level (60 ppm) and response time (465 ns) are almost comparable to those of the commercial Bi4Ge3O12 crystals. By the means of dispersing Lu1.98Bi0.02O3 nanoscintillators into organic polymer (PMMA)-acetone solution, the Lu1.98Bi0.02O3-PMMA flexible composite films exhibiting rapid response to X-ray photons, high X-ray sensitivity and radiation resistance, good mechanical performance and excellent environmental stability were prepared using a spin-coating technique. On the surface of X-ray imaging screen formed by the flexible dense composite films, the spatial resolution can reach to 6.0 lp/mm at a safe irradiation dose (4.6 μGy). Meanwhile, for the imaging screen using the flexible composite films after bended for thousands of times, we can observe clear image of each reed gap (300 μm) of the music box. For the Lu2O3:Bi3+-PMMA composite films, our results suggest that not only their scintillation properties are almost comparable to those of the commercial broadband Bi4Ge3O12 crystals, but also they might be applied in large-area and non-planar X-ray imaging.

Efficient production of ligand-free microscintillators at gram-scale for high-resolution X-ray luminescence imaging

The efficient production of high-quality scintillators with long radioluminescence afterglow is crucial for high-performance X-ray luminescence extension imaging. However, scaling-up the synthesis of ligand-free scintillators to fabricate large-area X-ray imaging screens for industrial applications remains a challenge. In this study, we report an efficient method to synthesize ligand-free, lanthanide-doped microscintillators by a one-pot reaction via the concentrated hydrothermal method. The as-synthesized microscintillators exhibit prolonged persistent radioluminescence for up to 30 days after X-ray exposure and remain high stability in air or water for more than 18 months without deterioration. Monte Carlo simulations indicate that the size effect is responsible for the excellent afterglow performance of the microscintillators. We employ these high-quality lanthanide-doped microscintillators to fabricate a large-area X-ray imaging detector using a blade-coating method, a spatial resolution of 24.9 lp/mm for X-ray imaging. Our study offers a solution for scaling-up the synthesis of low-cost microscintillators for practical applications.

Multispectral Large-Panel X-ray Imaging Enabled by Stacked Metal Halide Scintillators.

Conventional energy-integration black-white X-ray imaging lacks the spectral information of X-ray photons. Although X-ray spectra (energy) can be distinguished by the photon-counting technique typically with CdZnTe detectors, it is very challenging to be applied to large-area flat-panel X-ray imaging (FPXI). Herein, multilayer stacked scintillators of different X-ray absorption capabilities and scintillation spectra are designed; in this scenario, the X-ray energy can be discriminated by detecting the emission spectra of each scintillator; therefore, multispectral X-ray imaging can be easily obtained by color or multispectral visible-light camera in a single shot of X-rays. To verify this idea, stacked multilayer scintillators based on several emerging metal halides are fabricated in a cost-effective and scalable solution process, and proof-of-concept multispectral (or multi-energy) FPXI are experimentally demonstrated. The dual-energy X-ray image of a "bone-muscle" model clearly shows the details that are invisible in conventional energy-integration FPXI. By stacking four layers of specifically designed multilayer scintillators with appropriate thicknesses, a prototype FPXI with four energy channels is realized, proving its extendibility to multispectral or even hyperspectral X-ray imaging. This study provides a facile and effective strategy to realize multispectral large-area flat-panel X-ray imaging.

Fabrication of nanocrystalline Ga2O3-NiO heterojunctions for large-area low-dose X-ray imaging

The Ga2O3 photoconductor possesses a wide bandgap, a relatively large density and a high absorption coefficient for low-energy X-ray. Therefore, it is expected to realize a highly sensitive low-energy X-ray detector. Realizing p-n heterojunctions using Ga2O3 thin film is essential for large-area low-dose X-ray imaging. Here, a p-n diode consisting of nanocrystalline Ga2O3 thin film and NiO thin film is successfully prepared by electron beam evaporation, exhibiting a large current rectification ratio of 6.0 × 104. The p-n heterojunction shows a large valence band offset of 1.7 eV, a large conduction band offset of 0.84 eV and a built-in potential of 0.2 eV near the interfacial region, benefiting for separation and migration of photogenerated carriers. In addition, the photoconductive gain mechanism of Ga2O3/NiO heterojunction based X-ray detectors with optimized NiO thickness is investigated, achieving a high internal gain (3.3 × 103), a high sensitivity (3.4 × 104 μCGyair−1 cm−2), a low detection limit (42 μGyair s−1) and a short response time (2.2 ms). The optimized detectors with 10 × 10 pixels show a uniform X-ray response, demonstrating their promising use in large-area X-ray imaging applications.

Solvent co-assembly in lead-free perovskite scintillators for stable and large-area X-ray imaging

We report two 0D lead-free perovskite structures co-assembled from solvent molecules. The solvent co-assembled perovskite single-crystal exhibits excellent moisture stability and the wafer shows potential applications in large area X-ray imaging.

Advanced X-ray imaging at beamline 07 of the SAGA Light Source.

The SAGA Light Source provides X-ray imaging resources based on high-intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi-monochromatic SR obtained by the newly installed water-cooled metal filter and monochromatic SR selected by a Ge double-crystal monochromator (DCM) with high-resolution lens-coupled X-ray imagers, fast and low-dose micro-computed tomography (CT), fast phase-contrast CT using grating-based X-ray interferometry, and 2D micro-X-ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large-area fiber-coupled X-ray imagers, high-sensitivity phase-contrast CT using crystal-based X-ray interferometry can be performed. Low-temperature CT can be performed using the newly installed cryogenic system, and time-resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time-resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented.

Fast-response X-ray detector based on nanocrystalline Ga2O3 thin film prepared at room temperature

X-ray detectors have broad applications in the fields of medical imaging, security checks, industrial inspections, and scientific research. However, it is still challenging to develop X-ray detectors with fast response, high sensitivity, and stable direct conversion. In this study, we fabricated a fast-response X-ray detector based on a nanocrystalline Ga2O3 thin film, prepared by electron beam evaporation without a high-temperature post-annealing process. The structure characterization results show that Ga2O3 films were nanocrystalline, and a coplanar metal/semiconductor/metal (MSM)-structured X-ray detector was fabricated. The detection sensitivity reached up to 138.80 μCmGyair−1 cm−3 (at 50 V bias voltage), and the dark current was 50 pA (at 10 V bias voltage). In addition, the rise time and fall time of the transient photocurrent were measured (<35 ms) at an X-ray dose rate of 28.79 mGyairs−1, and there was no distinct persistent photocurrent (PPC) effect. The low defect density arising from the good crystalline structure of the Ga2O3 thin films is the major reason for the fast response of the device. These results show that nanocrystalline Ga2O3 thin films are promising materials for large-area X-ray imaging.

A new generation of direct X-ray detectors for medical and synchrotron imaging applications

Large-area X-ray imaging is one of the most widely used imaging modalities that spans several scientific and technological fields. Currently, the direct X-ray conversion materials that are being commercially used for large-area (> 8 cm × 4 cm without tiling) flat panel applications, such as amorphous selenium (a-Se), have usable sensitivities of up to only 30 keV. Although there have been many promising candidates (such as polycrystalline HgI2 and CdTe), none of the semiconductors were able to assuage the requirement for high energy (> 40 keV) large-area X-ray imaging applications due to inadequate cost, manufacturability, and long-term performance metrics. In this study, we successfully demonstrate the potential of the hybrid Methylammonium lead iodide (MAPbI3) perovskite-based semiconductor detectors in satisfying all the requirements for its successful commercialization in synchrotron and medical imaging. This new generation of hybrid detectors demonstrates low dark current under electric fields needed for high sensitivity X-ray imaging applications. The detectors have a linear response to X-ray energy and applied bias, no polarization effects at a moderate bias, and signal stability over long usage durations. Also, these detectors have demonstrated a stable detection response under BNL’s National Synchrotron Light Source II (NSLS-II) 70 keV monochromatic synchrotron beamline.

Backside Illuminated 3-D Photosensitive Thin-Film Transistor on a Scintillating Glass Substrate for Indirect-Conversion X-Ray Detection

A conventional large-area indirect-conversion X-ray detector usually adopts front side illumination (FSI) of a scintillator atop a photodiode-integrated thin-film transistor (TFT) array. This work however proposes a backside illuminated (BSI) three-dimensional dual-gate photosensitive a-Si:H TFT (3-D DGTFT) on a scintillating glass substrate, aiming for indirect-conversion X-ray detection. It not only improves the sensitivity with a 3-D photosensitive TFT as an active pixel sensor, but also enhances the resolution and photon utilization by reducing photon scattering and optical crosstalk. Backside illumination of 3-D photosensitive TFT-integrated scintillating glass therefore provides an alternative approach to large-area indirect-conversion X-ray imaging.

Dimension dependent immunity of X-ray irradiation on low-temperature polycrystalline-silicon TFTs

Typically, each element in a large-area flat-panel X-ray image sensor consists of a photodetector and amorphous silicon (a-Si) thin-film transistor (TFT) switches. In order to reduce noise, increase sensor dynamic range, and increase carrying capacity, the low-temperature polycrystalline-silicon (LTPS) TFTs have been proposed as a candidate to replace the a-Si TFTs. However, there are concerns regarding the impact of X-ray radiation in LTPS-TFTs, and several studies have been conducted to inquire into the same. In this paper, we show that LTPS TFTs with small channel length (<2 µm) are almost immune to X-ray radiation.

The PixFEL project: Progress towards a fine pitch X-ray imaging camera for next generation FEL facilities

The INFN PixFEL project is developing the fundamental building blocks for a large area X-ray imaging camera to be deployed at next generation free electron laser (FEL) facilities with unprecedented intensity. Improvement in performance beyond the state of art in imaging instrumentation will be explored adopting advanced technologies like active edge sensors, a 65nm node CMOS process and vertical integration. These are the key ingredients of the PixFEL project to realize a seamless large area focal plane instrument composed by a matrix of multilayer four-side buttable tiles. In order to minimize the dead area and reduce ambiguities in image reconstruction, a fine pitch active edge thick sensor is being optimized to cope with very high intensity photon flux, up to 104 photons per pixel, in the range from 1 to 10keV. A low noise analog front-end channel with this wide dynamic range and a novel dynamic compression feature, together with a low power 10bit analog to digital conversion up to 5MHz, has been realized in a 110μm pitch with a 65nm CMOS process. Vertical interconnection of two CMOS tiers will be also explored in the future to build a four-side buttable readout chip with high density memories. In the long run the objective of the PixFEL project is to build a flexible X-ray imaging camera for operation both in burst mode, like at the European X-FEL, or in continuous mode with the high frame rates anticipated for future FEL facilities.

A robust large area x-ray imaging system based on 100 μ m thick Gas Electron Multiplier

We have developed an imaging detector based on a non-standard GEM, made from a 100 μ m thick kapton foil (2-fold thicker than standard GEM's). The 100 micron thick GEM is produced using the same wet etching technique as the standard GEM and is less prone to the damage caused by discharges, creating a robust detector that can safely operate at high gain.In this work we present the results obtained with a cascaded gaseous electron multiplier composed by two 100 micron thick GEM and a 10× 10 cm2 bi-dimensional readout electrode with resistive charge division. We have recorded energy resolution of 21% and charge gains above 104 when the detector was irradiated with 5.9 keV X-rays emitted by a 55Fe radioactive source. We also present 10× 10 cm2 images acquired with the detector when irradiated with X-rays. The minimum position resolution recorded was 1.7 mm.

Large area CMOS active pixel sensor x-ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization.

Large area x-ray imagers based on complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology have been proposed for various medical imaging applications including digital breast tomosynthesis (DBT). The low electronic noise (50-300 e-) of CMOS APS x-ray imagers provides a possible route to shrink the pixel pitch to smaller than 75 μm for microcalcification detection and possible reduction of the DBT mean glandular dose (MGD). In this study, imaging performance of a large area (29×23 cm2) CMOS APS x-ray imager [Dexela 2923 MAM (PerkinElmer, London)] with a pixel pitch of 75 μm was characterized and modeled. The authors developed a cascaded system model for CMOS APS x-ray imagers using both a broadband x-ray radiation and monochromatic synchrotron radiation. The experimental data including modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE) were theoretically described using the proposed cascaded system model with satisfactory consistency to experimental results. Both high full well and low full well (LFW) modes of the Dexela 2923 MAM CMOS APS x-ray imager were characterized and modeled. The cascaded system analysis results were further used to extract the contrast-to-noise ratio (CNR) for microcalcifications with sizes of 165-400 μm at various MGDs. The impact of electronic noise on CNR was also evaluated. The LFW mode shows better DQE at low air kerma (Ka<10 μGy) and should be used for DBT. At current DBT applications, air kerma (Ka∼10 μGy, broadband radiation of 28 kVp), DQE of more than 0.7 and ∼0.3 was achieved using the LFW mode at spatial frequency of 0.5 line pairs per millimeter (lp/mm) and Nyquist frequency ∼6.7 lp/mm, respectively. It is shown that microcalcifications of 165-400 μm in size can be resolved using a MGD range of 0.3-1 mGy, respectively. In comparison to a General Electric GEN2 prototype DBT system (at MGD of 2.5 mGy), an increased CNR (by ∼10) for microcalcifications was observed using the Dexela 2923 MAM CMOS APS x-ray imager at a lower MGD (2.0 mGy). The Dexela 2923 MAM CMOS APS x-ray imager is capable to achieve a high imaging performance at spatial frequencies up to 6.7 lp/mm. Microcalcifications of 165 μm are distinguishable based on reported data and their modeling results due to the small pixel pitch of 75 μm. At the same time, potential dose reduction is expected using the studied CMOS APS x-ray imager.

Characterization and Comparison of Detector Systems for Large Area X-ray Imaging

Characterization and Comparison of Detector Systems for Large Area X-ray Imaging

Development of an x-ray detector based on polymer- dispersed liquid crystal

The applications of active matrix flat-panel imagers (AMFPIs) in large-area x-ray imaging systems have increased over time but are still severely limited owing to its pixel resolution, complex fabrication processes, and high cost. As a solution, x-ray light valve (XLV) technology was introduced and expected to have a better resolution and contrast ratio than those of AMFPI, owing to its micrometer level of the LC cells and signal amplification by an external light source. The twisting angle of the LC cells was changed by charge carrier signals created in a photoconductor layer against x-rays, and the diagnostic images from XLV were acquired from the transmittance of the external light source. However, there was a possibility that the photoconductor layer may be crystallized or degenerated due to the application of high temperatures for sealing the LC layer during the fabrication process. To solve such problems, polymer-dispersed liquid crystals (PDLCs), which do not need high temperature for the sealing process of the LC layer, are used in this study instead of typical LC cells. A photoconductor and PDLC are combined to develop an x-ray detector. An external light source and optical sensor are used to investigate the light transmission of the PDLC . The PDLCs used in this paper do not need polarizers and are self-adhesive. Hence, the transmittance is very high in the transparent state, which allows for a linear x-ray response and sufficient dynamic range in digital radiography.

X-Ray Imaging Using LEKIDs

We present the detection of 5.9 keV X-rays in a silicon wafer utilising an array of frequency multiplexed Kinetic Inductance Detectors. The readout electronics consists of a programmable digital electronics with an integrated 12-bit ADC, operating with a maximum frequency of 100 MHz. We implement a lumped element geometry, realising pixels as small as possible in order to achieve better position resolution. The whole system allows the simultaneous readout of 14 pixels with a bandwidth of 300 kHz, but it is easily scalable up to 100 pixels. A higher bandwidth detection, with less pixels, allows the reconstruction of the photon absorption position in the substrate up to hundreds of microns. This technological development could be applied in the next future to large area X-Ray Imaging. A better understanding of high energy photon and particle detection is also crucial for the space implementation of LEKIDs for mm-astronomy, where data loss due to Cosmic particles could be a major issue.

Feasibility study of direct-conversion x-ray detection using cadmium zinc telluride films

Polycrystalline Cd(Zn)Te films deposited by vacuum thermal evaporation are investigated as a direct-conversion medium for x-ray detection. The use of evaporation techniques allows for the preparation of large-area films with the potential for large-area x-ray imaging with high spatial resolution. Films with compositions of Cd1−xZnxTe (x = 0.15,0.25,0.3) were prepared to a thickness of 20 μm on slide glass substrates with an aluminum or indium tin oxide (ITO) bottom electrode and a silver top electrode, with and without additional charge-blocking layers (CeO2 and parylene dielectric) between the electrode and CdZnTe film to reduce leakage current. Composition and structural analyses of the as-deposited films confirm the development of polycrystalline CdZnTe. Leakage current in the CdZnTe film is approximately ten times lower than for a comparable CdTe film, and the lowest leakage is obtained for a film with composition of Cd0.7Zn0.3Te The use of ITO rather than aluminum as the bottom electrode provides a further improvement in leakage current and improved stability. The Cd0.7Zn0.3Te-based device with ITO electrode and charge-blocking layers achieves the highest total output charge (180.44 pC/cm2 or 1.1 × 109 e−/cm2) and signal-to-noise ratio (6.19 at applied bias of 30 V). The present experiments show that Cd1−xZnxTe in a multilayer structure with charge-blocking layers is feasible as a good radiation conversion layer for flatpanel radiation imaging systems.

High Speed, High Resolution and Large Area X-ray Imaging Using Silicon Drift Detectors

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Edgeless silicon sensors for Medipix-based large-area X-ray imaging detectors

Some X-ray imaging applications demand sensitive areas exceeding the active area of a single sensor. This requires a seamless tessellation of multiple detector modules with edgeless sensors. Our research is aimed at minimising the insensitive periphery that isolates the active area from the edge. Reduction of the edge-defect induced charge injection, caused by the deleterious effects of dicing, is an important step.We report on the electrical characterisation of 300 μm thick edgeless silicon p+-ν-n+ diodes, diced using deep reactive ion etching. Sensors with both n-type and p-type stop rings were fabricated in various edge topologies. Leakage currents in the active area are compared with those of sensors with a conventional design. As expected, we observe an inverse correlation between leakage-current density and both the edge distance and stop-ring width. From this correlation we determine a minimum acceptable edge distance of 50 μm. We also conclude that structures with a p-type stop ring show lower leakage currents and higher breakdown voltages than the ones with an n-type stop ring.