High-resolution Imaging Detector Research Articles

Visible Radiophotoluminescence of Color Centers in Lithium Fluoride Thin Films for High Spatial Resolution Imaging Detectors for Hard X-rays

Passive solid-state detectors based on the visible radiophotoluminescence (RPL) of stable aggregate F2 and F3 + color centers in lithium fluoride (LiF) are successfully used for X-ray imaging and advanced diagnostics of intense X-rays sources. Among their advantages, these detectors offer a wide dynamic range and simplicity of use. They can be read non-destructively using a fluorescence microscope, enabling high spatial resolution over a large field of view. Optically transparent LiF films, of three different increasing thicknesses, were grown by thermal evaporation on glass and silicon substrates and subsequently irradiated with monochromatic 7 keV X-rays at several doses from 1.3 × 101 to 4.5 × 103 Gy at the SOLEIL synchrotron facility. For all the LiF films, the RPL response was found to depend linearly on the irradiation dose, with films grown on Si(100) substrates exhibiting up to a 50% higher response compared to those grown on glass. A minimum dose of 13 Gy was detected, despite the low thickness of the irradiated films. The limited thickness of the homogeneously colored LiF film allowed to obtain a spatial resolution of (0.44 ± 0.04) μm in edge-enhancement imaging experiments conducted by placing an Au mesh in front of the samples.

High-resolution 3D X-ray diffraction microscopy: 3D mapping of deformed metal microstructures.

Three-dimensional X-ray diffraction microscopy, 3DXRD, has become an established tool for orientation and strain mapping of bulk polycrystals. However, it is limited to a finite spatial resolution of ∼1.5-3 µm. Presented here is a high-resolution modality of the technique, HR-3DXRD, for 3D mapping of submicrometre-sized crystallites or subgrains with high spatial and angular resolution. Specifically, the method is targeted to visualization of metal microstructures at industrially relevant degrees of plastic deformation. Exploiting intrinsic crystallographic properties of such microstructures, the high resolution is obtained by placing a high-resolution imaging detector in between the near-field and far-field regimes. This configuration enables 3D mapping of deformation microstructure by determining the centre of mass and volume of the subgrains and generating maps by tessellation. The setup is presented, together with a data analysis approach. Full-scale simulations are used to determine limitations and to demonstrate HR-3DXRD on realistic phantoms. Misalignments in the setup are shown to cause negligible shifts in the position and orientation of the subgrains. Decreasing the signal-to-noise ratio is observed to lead primarily to a loss in the number of determined diffraction spots. Simulations of an α-Fe sample deformed to a strain of ε vM = 0.3 and comprising 828 subgrains show that, despite the high degree of local texture, 772 of the subgrains are retrieved with a spatial accuracy of 0.1 µm and an orientation accuracy of 0.0005°.

Real-Time Inference With 2D Convolutional Neural Networks on Field Programmable Gate Arrays for High-Rate Particle Imaging Detectors.

We present a custom implementation of a 2D Convolutional Neural Network (CNN) as a viable application for real-time data selection in high-resolution and high-rate particle imaging detectors, making use of hardware acceleration in high-end Field Programmable Gate Arrays (FPGAs). To meet FPGA resource constraints, a two-layer CNN is optimized for accuracy and latency with KerasTuner, and network quantization is further used to minimize the computing resource utilization of the network. We use “High Level Synthesis for Machine Learning” (hls4ml) tools to test CNN deployment on a Xilinx UltraScale+ FPGA, which is an FPGA technology proposed for use in the front-end readout system of the future Deep Underground Neutrino Experiment (DUNE) particle detector. We evaluate network accuracy and estimate latency and hardware resource usage, and comment on the feasibility of applying CNNs for real-time data selection within the currently planned DUNE data acquisition system. This represents the first-ever exploration of employing 2D CNNs on FPGAs for DUNE.

Recent Development in X-Ray Imaging Technology: Future and Challenges.

X-ray imaging is a low-cost, powerful technology that has been extensively used in medical diagnosis and industrial nondestructive inspection. The ability of X-rays to penetrate through the body presents great advances for noninvasive imaging of its internal structure. In particular, the technological importance of X-ray imaging has led to the rapid development of high-performance X-ray detectors and the associated imaging applications. Here, we present an overview of the recent development of X-ray imaging-related technologies since the discovery of X-rays in the 1890s and discuss the fundamental mechanism of diverse X-ray imaging instruments, as well as their advantages and disadvantages on X-ray imaging performance. We also highlight various applications of advanced X-ray imaging in a diversity of fields. We further discuss future research directions and challenges in developing advanced next-generation materials that are crucial to the fabrication of flexible, low-dose, high-resolution X-ray imaging detectors.

High-Resolution Thermal Neutron Imaging With ¹⁰Boron/CsI:Tl Scintillator Screen

High-resolution neutron imaging is difficult, due to the low-light output of neutron scintillators, and the spread of light within common neutron-sensitive scintillators as well as the spread of intermediate particles occurring during the detection process. To address this issue, we have developed a highresolution scintillator for neutron imaging by combining enriched <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B with the well-known CsI:Tl scintillator films. CsI:Tl has excellent properties for X-ray imaging applications, due to a high light yield of 60 000 photons/MeV, and high spatial resolution, which derives from its microcolumnar structure, which channels scintillation light to the photodetector. To enable CsI:Tl to detect neutrons, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B (96% enriched) was deposited by electron beam directly onto the CsI:Tl film, making a layered scintillator structure in which the alphas produced by the neutron interaction with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B are detected in the CsI:Tl. The <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B layer was approximately 3 μm thick, while the thickness of the CsI:Tl film was 11 μm. These novel layered scintillators were integrated into the high-resolution neutron imaging detector [“Paul Scherer Institute (PSI) Neutron Microscope”] at the Pulse OverLap DIffractometer (POLDI) beamline at the PSI. With our <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B/CsI:Tl scintillator, we were able to achieve a spatial resolution down to 9 μm. To demonstrate the effectiveness of the layered scintillator, we present results obtained by thermal neutron imaging as well as high-resolution neutron-computed tomography. Finally, we believe there is considerable scope for future optimization of the performance of this system.

X-ray phase-sensitive imaging using a bilens interferometer based on refractive optics.

The phase-sensitive X-ray imaging technique based on the bilens interferometer is developed. The essence of the method consists of scanning a sample, which is set upstream of the bilens across the beam of one lens of the interferometer by recording changes in the interference pattern using a high-resolution image detector. The proposed approach allows acquiring the absolute value of a phase shift profile of the sample with a fairly high phase and spatial resolution. The possibilities of the imaging technique were studied theoretically and experimentally using fibres with different sizes as the test samples at the ESRF ID06 beamline with 12 keV X-rays. The corresponding phase shift profile reconstructions and computer simulations were performed. The experimental results are fully consistent with theoretical concepts and appropriate numerical calculations. Applications of the interferometric imaging technique are discussed, as well as future improvements.

A simulation study of a high-resolution fast neutron imaging detector based on liquid scintillator loaded capillaries

At present, the highest spatial resolution of a fast neutron imaging detector, mainly determined by the range of secondary particles generated by fast neutrons, is about hundreds of microns. In view of the above inherent spatial resolution limitation, a capillary-based scintillation detector that can improve the spatial resolution of fast neutron imaging by recording and reconstructing the recoil proton track was developed. The purpose of this paper is to develop a detector for recognizing recoil proton events, reconstructing particle track and improving the position resolution with track reconstruction method to reconstruct the position of interaction. The proposed detector consists of a 1000 × 1000 array of glass capillaries loaded with a high refractive index liquid scintillator. Each glass capillary was 10 μm in diameter and 5 cm in length. The recoil protons generated by the incident neutrons move within the detector and produce scintillation light within each capillary that they traverse. The light emitted from the capillary array can be recorded by employing an intensified CCD camera. We used Geant4 to simulate the detector performance and CERN ROOT analysis framework to record physical information of recoil proton, including position, energy deposition in each capillary and track length. Based on Hough transform, a rapid, computerized and efficient proton track reconstruction procedure was developed. The recoil proton events display a continuous extended structure. The track reconstruction algorithms can reconstruct individual track precisely, and when the counting rate was relatively low, the track reconstruction results were in good agreement with simulation data. Moreover, for intensive overlap conditions, this algorithm also reconstructs periphery tracks with high rate of accuracy.

Super-resolution algorithm applied to images acquired at millimeter wave frequency in single pixel and computational ghost imaging configurations

ABSTRACTThe lack of low cost, high-resolution two-dimensional imaging detectors and the expensiveness of the measurements make millimeter wave imaging challenging. Single detector configurations are promising to solve data acquisition problem in millimeter wave imaging. In this study, millimeter wave imaging in transmission mode is done with single pixel imaging and computational ghost imaging configurations. In order to reduce the number of measurements in each configuration, Compressed Sensing architecture is used. To increase the image resolution, software-based super-resolution is applied. To the best of our knowledge, this is first study comparing the computational ghost imaging with single pixel imaging, besides software-based super-resolution method is applied to the real world millimeter wave images. It is seen that super-resolution increases the quality in both configurations while computational ghost imaging has better quality compared to single pixel imaging in millimeter waves.

Performance evaluation for a radiation imaging detector using single-crystal GPS (Ce) plate

Cerium doped gadolinium pyrosilicate (GPS (Ce), Gd2Si2O7), which is a scintillator with a high light output, is a likely candidate to develop high-resolution radiation imaging detectors. Thus we fabricated a GPS (Ce) imaging detector using a single-crystal GPS (Ce) plate in combination with a position-sensitive photomultiplier tube (PSPMT). Through a performance evaluation, we found that the spatial resolution was ∼ 0.5 mm FWHM for Am-241 α particles (5.5 MeV) with an energy resolution of 15% FWHM. The decay time difference of GPS (Ce) between 5.5 MeV α particles and 662 keV Cs-137 γ photons was 7 ns, which was insufficient to separate each image using pulse-shape discrimination. However, the α/γ ratio was large (0.35), so it was possible to separate 5.5 MeV α particles and 662 keV Cs-137 γ photons by the energy spectra. We conclude that the imaging detector using single-crystal GPS (Ce) is promising for radiation, especially for α particles.

Development of a YAP(Ce) camera for the imaging of secondary electron bremsstrahlung x-ray emitted during carbon-ion irradiation toward the use of clinical conditions

Low-energy x-ray imaging of the secondary electron bremsstrahlung (SEB) x-ray emitted during carbon-ion irradiation is a promising method for range estimation. However, it remains unclear whether the method can be used for imaging with the clinical dose levels of carbon-ion and whether the bremsstrahlung x-ray can be detected from the deeper part of the body. To clarify these points, we developed a new high resolution low-energy x-ray camera and conducted imaging of the SEB x-ray during the irradiation of carbon-ions of different energies and intensities. Imaging was also tried with an x-ray camera using a human-head-sized, 17 cm diameter cylindrical phantom. To develop a high resolution imaging detector for a low-energy x-ray, we used a 20 × 20 × 0.5 mm thick cerium-doped yttrium aluminum perovskite, YA1O3 (YAP(Ce)) scintillator plate, which was optically coupled to a 25 mm square high quantum efficiency (HQE) type position sensitive photomultiplier tube (PSPMT). The imaging detector was encased in a 2 cm thick tungsten container and a pinhole collimator was attached to its camera head. After evaluating the camera’s performance, SEB x-ray imaging was tried during irradiation of the carbon-ion and compared the results with a Monte Carlo simulation. We imaged the beam tracks by the SEB x-ray in real-time during irradiation of the carbon-ion and imaging and range estimation were possible even with near clinical dose level of 7.5 × 108 particles of carbon-ion. Clear images of a SEB x-ray were also obtained for a 17 cm diameter cylindrical phantom. The measured images were good agreement with the Monte Carlo simulation. We confirmed that our developed YAP(Ce) camera is promising for imaging SEB x-rays during irradiation of carbon-ions even near clinical conditions.

Development of an X-ray imaging detector to resolve 200 nm line-and-space patterns by using transparent ceramics layers bonded by solid-state diffusion.

A high-resolution lens-coupled X-ray imaging detector equipped with a thin-layer transparent ceramics scintillator has been developed. The scintillator consists of a 5μm thick Ce-doped Lu3Al5O12 layer (LuAG:Ce) bonded onto the support substrate of the non-doped LuAG ceramics by using a solid-state diffusion technique. Secondary electron microscopy of the bonded interface indicated that the crystal grains were densely packed without any pores in the optical wavelength scale, indicating a quasi-uniform refractive index across the interface. This guarantees high transparency and minimum reflection, which are essential properties for X-ray imaging detectors. The LuAG:Ce scintillator was incorporated into an X-ray imaging detector coupled with an objective lens with a numerical aperture of 0.85 and an optical magnification of 100. The scintillation light was imaged onto a complementary metal-oxide-semiconductor image sensor. The effective pixel size on the scintillator plane was 65nm. X-ray transmission images of 200nm line-and-space patterns were successfully resolved. The high spatial resolution was demonstrated by X-ray transmission images of large integrated circuits with the wiring patterns clearly visualized.

Operando Neutron Imaging for Next-Generation Solid State Batteries: A Direct Visualization of Li-Ion Transport in Sulfide Materials

Li-ion all-solid-state batteries promise to enhance safety and performance compared to conventional liquid based batteries. Nevertheless, only few investigations have been carried out on the effect of the solid electrolyte’s ionic conductivity on the electrochemical performance of batteries in order to visualize non-uniform fields of transport. Neutron Imaging (NI) is a non-intrusive technique that offers the possibility of tracking light elements such as the 6Li isotope during all phases of battery operation. Because it helps visualizing lithium’s concentration profiles, NI allows quantifying Li-ion transport and enables us to model solid state batteries. We therefore expect NI to help us explain solid state batteries’ poor rate capabilities. A reliable electrochemical cell was successfully designed and utilized for an operando test of an all-solid-state battery using PSI's high-resolution neutron imaging detector ('Neutron Microscope') at the POLDI beamline of Swiss Spallation Neutron Source SINQ (Paul Scherrer Institut). A solid state battery with a composite electrode TiS2:6Li3PS4(6LPS) and a 6Li-In alloy counter electrode have been investigated (Figure 1) and the results will be discussed. Figure 1

A large area high resolution imaging detector for fast atom diffraction

We describe a high resolution imaging detector based on a single 80 mm micro-channel-plate (MCP) and a phosphor screen mounted on a UHV flange of only 100 mm inner diameter. It relies on standard components and we describe its performance with one or two MCPs. A resolution of 80 $\mu m$ rms is observed on the beam profile. % which is limited by the camera pixel size. At low count rate, individual impact can be pinpointed with few $\mu m$ accuracy but the resolution is probably limited by the MCP channel diameter. The detector has been used to record the diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD), a technique probing the electronic density of the topmost layer only. The detector was also used to record the scattering profile during azimuthal scan of the crystal to produce triangulation curves revealing the surface crystallographic directions of molecular layers. It should also be compatible with reflection high energy electron (RHEED) experiment when fragile surfaces require a low exposure to the electron beam.

Anti-scatter grid artifact elimination for high-resolution x-ray imaging detectors without a prior scatter distribution profile.

Using anti-scatter grids with high-resolution imaging detectors could result in grid-line artifacts, with increasing severity as detector resolution improves. Grid-line mask subtraction can result in residual artifacts that are due to residual scatter penetrating the grid and not subtracted. By subtracting this residual scatter, the grid artifacts can be minimized. In the previous works, an initial residual-scatter estimate was derived by placing lead markers on a test object; however, any change in the object geometry requires a new scatter estimate. Such a method is impractical to implement during a clinical procedure. In this work, we present a new method to derive the initial scatter estimate to eliminate grid-line artifacts during a procedure. A standard stationary Smit-Roentgen x-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector (Dexela Model 1207, pixel size - 75 μm) to image an anthropomorphic head phantom. The initial scatter estimate was derived from the image itself and the grid artifacts were eliminated using recursive correction estimation; this result was compared to that with the estimate derived from placing lead markers on the phantom. In both cases, the contrast-to-noise ratio (CNR) was improved compared to the original image with grid artifacts. Percentage differences in CNR's for three regions between the images corrected with the two estimates were less than 5%. With the new method no a priori scatter distribution profiles are needed, eliminating the need to have libraries of pre-calculated scatter profiles and making the implementation more clinically practical.

Development of the “GP2” Detector: Modification of the PImMS CMOS Sensor for Energy-Resolved Neutron Radiography

This paper reports on the development and commissioning of the GP2 detector. GP2 was developed to address the requirement for a high-resolution event-mode imaging detector, for application in energy-resolved neutron radiography. The name GP2 derives from the use of gadolinium as a neutron conversion material, combined with a second-generation mass spectrometry sensor known as PImMS2. Theoretical and measured characteristics of GP2 are compared, with emphasis on the usability and functionality of the detector. The development of the detector has been steered by a design philosophy which was established to ensure that the detector has unique and novel impact. The motivation and consequences of the design philosophy are discussed. The key parameters reported are the neutron detection efficiency (7.5% at 2.5 A), gamma sensitivity ( $1.5 \times 10^{-3})$ , and a spatial resolution (modulation transfer function at 10%) of 6.4 lp/mm for a 4- $\mu \text{m}$ -thick natural gadolinium neutron converter film.

A high-resolution CdTe imaging detector with multi-pinhole optics for in-vivo molecular imaging

High-resolution CdTe semiconductor detectors with both fine position resolution and high energy resolution hold great promise to improve measurement in various hard X-ray and gamma-ray imaging experiments. In the field of in-vivo molecular imaging, where the molecules labeled with radioisotopes are injected into a small animal and their distribution in a body is detected by gamma-ray imaging detectors externally, a large detection area is also required to obtain a number of projections from multiple pinholes. We have developed a prototype imaging system consisting of a 32 mm-wide CdTe double-sided strip detector equipped with multi-pinhole optics. We describe its imaging capability, as studied through experiments with radioisotopes for medical use (125I and 111In) and a 3D phantom.

Real time implementation of anti-scatter grid artifact elimination method for high resolution x-ray imaging CMOS detectors using Graphics Processing Units (GPUs).

Scatter is one of the most important factors effecting image quality in radiography. One of the best scatter reduction methods in dynamic imaging is an anti-scatter grid. However, when used with high resolution imaging detectors these grids may leave grid-line artifacts with increasing severity as detector resolution improves. The presence of such artifacts can mask important details in the image and degrade image quality. We have previously demonstrated that, in order to remove these artifacts, one must first subtract the residual scatter that penetrates through the grid followed by dividing out a reference grid image; however, this correction must be done fast so that corrected images can be provided in real-time to clinicians. In this study, a standard stationary Smit-Rontgen x-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector, the Dexela 1207 (pixel size - 75 micron) to image anthropomorphic head phantoms. For a 15 × 15 cm field-of-view (FOV), scatter profiles of the anthropomorphic head phantoms were estimated then iteratively modified to minimize the structured noise due to the varying grid-line artifacts across the FOV. Images of the head phantoms taken with the grid, before and after the corrections, were compared, demonstrating almost total elimination of the artifact over the full FOV. This correction is done fast using Graphics Processing Units (GPUs), with 7-8 iterations and total time taken to obtain the corrected image of only 87 ms, hence, demonstrating the virtually real-time implementation of the grid-artifact correction technique.

A high-resolution CMOS imaging detector for the search of neutrinoless double β decay in 82Se

We introduce high-resolution solid-state imaging detectors for the search of neutrinoless double β decay. Based on the present literature, imaging devices from amorphous 82Se evaporated on a complementary metal-oxide-semiconductor (CMOS) active pixel array could have the energy and spatial resolution to produce two-dimensional images of ionizing tracks of utmost quality, effectively akin to an electronic bubble chamber in the double β decay energy regime. Still to be experimentally demonstrated, a detector consisting of a large array of these devices could have very low backgrounds, possibly reaching 1 × 10−7/(kgy) in the neutrinoless decay region of interest (ROI), as it may be required for the full exploration of the neutrinoless double β decay parameter space in the most unfavorable condition of a strongly quenched nucleon axial coupling constant.

Scatter estimation and removal of anti-scatter grid-line artifacts from anthropomorphic head phantom images taken with a high resolution image detector.

In radiography, one of the best methods to eliminate image-degrading scatter radiation is the use of anti-scatter grids. However, with high-resolution dynamic imaging detectors, stationary anti-scatter grids can leave grid-line shadows and moiré patterns on the image, depending upon the line density of the grid and the sampling frequency of the x-ray detector. Such artifacts degrade the image quality and may mask small but important details such as small vessels and interventional device features. Appearance of these artifacts becomes increasingly severe as the detector spatial resolution is improved. We have previously demonstrated that, to remove these artifacts by dividing out a reference grid image, one must first subtract the residual scatter that penetrates the grid; however, for objects with anatomic structure, scatter varies throughout the FOV and a spatially differing amount of scatter must be subtracted. In this study, a standard stationary Smit-Rontgen X-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector, the Dexela 1207 (pixel size - 75 micron) to image anthropomorphic head phantoms. For a 15 × 15cm FOV, scatter profiles of the anthropomorphic head phantoms were estimated then iteratively modified to minimize the structured noise due to the varying grid-line artifacts across the FOV. Images of the anthropomorphic head phantoms taken with the grid, before and after the corrections, were compared demonstrating almost total elimination of the artifact over the full FOV. Hence, with proper computational tools, anti-scatter grid artifacts can be corrected, even during dynamic sequences.

Experimental setup and the system performance for single-grid-based phase-contrast x-ray imaging (PCXI) with a microfocus x-ray tube

In this work, we investigated a simplified approach to phase-contrast x-ray imaging (PCXI) by using a single antiscatter grid and a microfocus x-ray tube, which has potential to open the way to further widespread use of PCXI into the related application areas. We established a table-top setup for PCXI studies of biological and non-biological samples and investigated the system performance. The PCXI system consists of a focused-linear grid having a strip density of 200lines/in. (JPI Healthcare Corp.), a microfocus x-ray tube having a focal spot size of about 5μm (Hamamatsu, L7910), and a high-resolution CMOS imaging detector having a pixel size of 48μm (Rad-icon Imaging Corp., Shad-o-Box 2048). By using our prototype system, we successfully obtained attenuation, scattering, and differential phase-contrast x-ray images of improved visibility from the raw images of several samples at x-ray tube conditions of 50kVp and 6mAs. Our initial results indicate that the single-grid-based approach seems a useful method for PCXI with great simplicity and minimal requirements on the setup alignment.