High-resolution X-ray Detectors Research Articles

Pixel Circuit Design for X-ray Detection Utilizing a-IGZO Thin-Film Transistors

Abstract In recent advancements, X-ray detectors have made significant progress. Active pixel sensors exhibit superior Signal-to-Noise Ratio (SNR) compared to passive counterparts. The conventional pixel circuit for X-ray detectors has three transistors and one capacitor. We focused on simplifying this pixel to enhance resolution. Our research introduces and verifies a novel pixel circuit developed for high-resolution X-ray detectors. The proposed pixel circuit is composed by two n-type thin-film transistors and one capacitor. It requires two scan pulses and three operational stages. This structure can effectively reduce the component area of the pixel circuit. We designed RPI LEVEL = 35 amorphous TFT model and simulated for verify our proposed pixel circuit. In results, proposed pixel circuit successfully operated and shows 2.5 μV when the equivalent resistance of detector (RDetector) is 10 MΩ, and 8.38 V when RDetector is 1 MΩ. To minimize the harmful effects of X-ray exposure, reducing the dosage is essential. Sensitivity and low noise are crucial factors, and the proposed circuit offers a compact design, increased sensitivity, and higher output voltage.

Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications

We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

Prospects for detecting the circum- and intergalactic medium in X-ray absorption using the extended intracluster medium as a backlight

ABSTRACT The warm-hot plasma in cosmic web filaments is thought to comprise a large fraction of the gas in the local Universe. So far, the search for this gas has focused on mapping its emission, or detecting its absorption signatures against bright, point-like sources. Future, non-dispersive, high-spectral resolution X-ray detectors will, for the first time, enable absorption studies against extended objects. Here, we use the Hydrangea cosmological hydrodynamical simulations to predict the expected properties of intergalactic gas in and around massive galaxy clusters, and investigate the prospects of detecting it in absorption against the bright cores of nearby, massive, relaxed galaxy clusters. We probed a total of 138 projections from the simulation volumes, finding 16 directions with a total column density $N_{{\rm O\, {\small VII}}} > 10^{14.5}$ cm−2. The strongest absorbers are typically shifted by ±1000 km s−1 with respect to the rest frame of the cluster they are nearest to. Realistic mock observations with future micro-calorimeters, such as the Athena X-ray Integral Field Unit or the proposed Line Emission Mapper (LEM) X-ray probe, show that the detection of cosmic web filaments in ${\rm O\, {\small VII}}$ and ${\rm O\, {\small VIII}}$ absorption against galaxy cluster cores will be feasible. An ${\rm O\, {\small VII}}$ detection with a 5σ significance can be achieved in 10–250 ks with Athena for most of the galaxy clusters considered. The ${\rm O\, {\small VIII}}$ detection becomes feasible only with a spectral resolution of around 1 eV, comparable to that envisioned for LEM.

Customizable Scintillator of Cs3 Cu2 I5 :2% In+ @Paper for Large-Area X-Ray Imaging.

High-resolution X-ray imaging is increasingly required for medical diagnosis and large-area detection. However, the issues of scattering and optical crosstalk are limiting the spatial resolution of the indirect X-ray imaging. In this study, a feasible and efficient strategy is proposed to in situ synthesize flexible Cs3 Cu2 I5 :2%In+ @paper as a superior scintillator film, which can be scaled up to an ultra-large area of 4800 cm2 . The as-obtained Cs3 Cu2 I5 :2%In+ @paper performs a fascinating photoluminescence quantum efficiency up to 88.14%, a steady state light yield of 70169 photons/MeV, and spatial resolution of 15 lpmm-1 . Moreover, the suppressed physical scattering and optical crosstalk of the corresponding film are demonstrated. Accordingly, this work explores a feasible fabrication of customizable scintillation films with large area for high-resolution X-ray detection.

High temperature and water stable CaF2:Eu2+ glass ceramic for high resolution X-ray detection

The rising requirement for radiation detection materials for practical applications has inspired to burgeoning investigation of scintillator materials. High performance X-ray detection require high spatial resolution and long-term stability, particularly for targeted objects at extreme conditions. Here, the CaF2:Eu2+ glass ceramic (GC), in which the CaF2:Eu2+ nanoparticles are wrapped by the glassy matrix, is successfully obtained the melting method. The as-obtained CaF2:Eu2+ GC manifests bright blue radioluminescence (RL) emission peaked at 470 nm thanks to the effective 5d-4f transition of Eu2+ ions. In addition, the as-obtained CaF2:Eu2+ GC presents high transmittance of 84.2% and visible light, contributing an excellent spatial resolution of 15 lp/mm at room temperature. Importantly, the as-obtained CaF2:Eu2+ GC exhibits high robustness at water conditions and high thermal stability with X-ray resolution of 12.1 lp/mm at 473 K. Our work demonstrates that CaF2:Eu2+ GC scintillators provide an excellent visualization tool for high-resolution scintillators X-ray images in harsh conditions.

Ellipsometry Characterisation for the Cd1-xZnxTe1-ySey Semiconductor Used in X-ray and Gamma Radiation Detectors

The study of the optical properties of the Cd1-xZnxTe1-ySey (CZTS) crystal provides a clear idea about its response to incident X-ray or gamma radiation. This is important for selecting a proper composition of CZTS to achieve superior quality and high-resolution X-ray and gamma radiation detectors at room temperature and reduce their production cost. This article’s novelty is in lowering the cost of the optical and compositional characterisation of CZTS using the ellipsometry technique. The most significant successes achieved are the composition ellipsometry model determination of CZTS based on the Effective Medium Approximation (EMA) substrate of the binary compound CdTe and ZnSe with an oxide layer of CdTe and the experimental verification that the bandgap moves to lower energies with the addition of Se.

High spatial resolution direct conversion amorphous selenium X-ray detectors with monolithically integrated CMOS readout

Recent progress in the field of micron-scale spatial resolution direct conversion X-ray detectors for high-energy synchrotron light sources serve applications ranging from nondestructive and noninvasive microscopy techniques which provide insight into the structure and morphology of crystals, to medical diagnostic measurement devices. Amorphous selenium (a-Se) as a wide-bandgap thermally evaporated photoconductor exhibits ultra-low thermal generation rates for dark carriers and has been extensively used in X-ray medical imaging. Being an amorphous material, it can further be deposited over large areas at room temperatures and at substantially lower costs as compared to crystalline semiconductors. To address the demands for a high-energy and high spatial resolution X-ray detector for synchrotron light source applications, we have thermally evaporated a-Se on a Mixed-Mode Pixel Array Detector (MM-PAD) Application Specific Integrated Circuit (ASIC). The ASIC format consists of 128 × 128 square pixels each 150 μm on a side. A 200 μm a-Se layer was directly deposited on the ASIC followed by a metal top electrode. The completed detector assembly was tested with 45 kV Ag and 23 kV Cu X-ray tube sources. The detector fabrication, performances, Modulation Transfer Function (MTF) measurements, and simulations are reported.

A versatile laboratory setup for high resolution X-ray phase contrast tomography and scintillator characterization.

X-ray micro-tomography (μCT) is a powerful non-destructive 3D imaging method applied in many scientific fields. In combination with propagation-based phase-contrast, the method is suitable for samples with low absorption contrast. Phase contrast tomography has become available in the lab with the ongoing development of micro-focused tube sources, but it requires sensitive and high-resolution X-ray detectors. The development of novel scintillation detectors, particularly for microscopy, requires more flexibility than available in commercial tomography systems. We aim to develop a compact, flexible, and versatile μCT laboratory setup that combines absorption and phase contrast imaging as well as the option to use it for scintillator characterization. Here, we present details on the design and implementation of the setup. We used the setup for μCT in absorption and propagation-based phase-contrast mode, as well as to study a perovskite scintillator. We show the 2D and 3D performance in absorption and phase contrast mode, as well as how the setup can be used for testing new scintillator materials in a realistic imaging environment. A spatial resolution of around 1.3μm is measured in 2D and 3D. The setup meets the needs for common absorption μCT applications and offers increased contrast in phase contrast mode. The availability of a versatile laboratory μCT setup allows not only for easy access to tomographic measurements, but also enables a prompt monitoring and feedback beneficial for advances in scintillator fabrication.

Designing Next Generation of Persistent Luminescence: Recent Advances in Uniform Persistent Luminescence Nanoparticles.

Persistent luminescence is a unique optical process where long-lasting afterglow persists after the cessation of excitation. Nanoscale persistent luminescent materials are getting increased research interest from various fields due to their unique optical property. In recent years, inspiring achievements have been made to produce uniform persistent luminescence nanoparticles (PLNPs) in a controllable manner, unleashing their fascinating potential, surpassing other types of luminescent materials in a wide variety of application such as high-contrast bioimaging and high-resolution X-ray detection. In this review, the evolution of uniform PLNPs, from their bulk phosphor counterparts, to the "top-down" preparation of nanoscale persistent luminescent materials, to the recent "bottom-up" synthesis of uniform PLNPs is first summarized. The respective milestones of uniform PLNPs prepared by templated synthesis, aqueous synthesis, and colloidal synthesis are highlighted. The key optical properties that can be enhanced in uniform PLNPs, including increasing the persistent luminescence intensity, tuning the excitation irradiance, as well as the emission wavelengths are then analyzed. Detailed strategies to enhance each optical property are also discussed in various sections. Finally, future challenges are highlighted with respect to the perspectives on the development of next-generation PLNPs with novel applications.

Single-shot grating-based X-ray phase contrast imaging via generative adversarial network

Talbot-Lau interferometry obtains X-ray differential phase contrast (DPC) signals of object by subtracting multiple moiré patterns acquired by phase-stepping (PS) procedure. Due to the need of multiple intensity measurements, the long measuring time is inevitable in the conventional DPC imaging, giving rise to X-ray dose and fluctuations. In this paper, we propose a single-shot X-ray phase contrast imaging (XPCI) method based on deep learning. Specifically, in hardware, we propose to replace the analysis absorption grating with the high-resolution X-ray detector system to avoid the illumination flux loss caused by the analysis grating. In software, we employ a U-net based generative adversarial network (GAN) for solving the phase reconstruction problem with single-shot intensity pattern. By examining the performance on a variety of simulated and experimental datasets, we demonstrate that our approach, in spite of only using single intensity pattern, is able to obtain results with high resolution and image contrast which is competitive with the conventional PS approach, while being less time-consuming and low-dose.

2D perovskite-based high spatial resolution X-ray detectors

X-ray radiography is the most widely used imaging technique with applications encompassing medical and industrial imaging, homeland security, and materials research. Although a significant amount of research and development has gone into improving the spatial resolution of the current state-of-the-art indirect X-ray detectors, it is still limited by the detector thickness and microcolumnar structure quality. This paper demonstrates high spatial resolution X-ray imaging with solution-processable two-dimensional hybrid perovskite single-crystal scintillators grown inside microcapillary channels as small as 20 µm. These highly scalable non-hygroscopic detectors demonstrate excellent spatial resolution similar to the direct X-ray detectors. X-ray imaging results of a camera constructed using this scintillator show Modulation Transfer Function values significantly better than the current state-of-the-art X-ray detectors. These structured detectors open up a new era of low-cost large-area ultrahigh spatial resolution high frame rate X-ray imaging with numerous applications.

Multimodal Digital X-ray Scanners with Synchronous Mapping of Tactile Pressure Distributions using Perovskites.

Visual and tactile information are the key intuitive perceptions in sensory systems, and the synchronized detection of these two sensory modalities can enhance accuracy of object recognition by providing complementary information between them. Herein, multimodal integration of flexible, high-resolution X-ray detectors with a synchronous mapping of tactile pressure distributions for visualizing internal structures and morphologies of an object simultaneously is reported. As a visual-inspection method, perovskite materials that convert X-rays into charge carriers directly are synthesized. By incorporating pressure-sensitive air-dielectric transistors in the perovskite components, X-ray detectors with dual modalities (i.e., vision and touch) are attained as an active-matrix platform for digital visuotactile examinations. Also, in vivo X-ray imaging and pressure sensing are demonstrated using a live rat. This multiplexed platform has high spatial resolution and good flexibility, thereby providing highly accurate inspection and diagnoses even for the distorted images of nonplanar objects.

A feasibility study of a high-resolution SiPM based detector for X-ray imaging

In the present report, we summarize the results of our efforts to create an X-ray counting detector based on silicon photomultipliers (SiPMs) for digital scanning radiography with a sub-millimeter resolution. To realize this detector, we produced samples of pixelated scintillators with a pitch of 250 μm using the laser ablation technology. To measure real detector parameters, we have built a detector prototype based on a 32-channel Omega EASIROC front-end chip and a linear SiPM array. The results obtained in this study demonstrated the possibility of creating such high-resolution X-ray detectors.

Imaging performances of an in-house compact high spatial resolution X-ray detector based on Electrowetting Liquid Lens

The performances of compact and efficient new X-ray detector for hard X-ray synchrotron applications have been evaluated. This detector consists of an indirect detector based on a thin scintillator coupled to a CMOS digital camera by an infinity corrected microscope objective and an electrowetting liquid lens. Using such an optical combination focuses the image by applying a simple stabilized current without any motorization, while keeping the same imaging performances. The optical properties in term of Modulation Transfer Function (MTF) and time stability have been measured at a visible wavelength and compared with a classical microscope. An X-ray microscope camera based on this proposed optical combination with a magnification of ten (10×) has been assembled and tested on a hard X-ray beamline at the SOLEIL synchrotron. A spatial resolution of 415 lp/mm (line of 1.2 μm wide) and an X-ray area gain of 2.2 ADU/ph have been measured for a 12 keV energy beam. Results have been compared with those obtained with a classical microscope and also with a theoretical model. The compact X-ray microscope proposed can fit close to the sample in order to measure the X-ray incident beam size and intensity. Coupled with high performance scientific CMOS camera, this system can be used, for example, in a very restricted space on X-ray microscopy tomography beamline environment for 3D X-ray micro-tomography reconstruction.

HREXI calibration facility: mapping out subpixel-level responses from high-resolution cadmium zinc telluride imaging x-ray detectors

The High-Resolution Energetic X-ray Imager (HREXI) cadmium zinc telluride (CZT) detector development program at Harvard is aimed at developing tiled arrays of finely pixelated CZT detectors for use in wide-field coded aperture 3 to 200 keV x-ray telescopes. A pixel size of ∼600 μm has already been achieved in the ProtoEXIST2 (P2) detector plane with CZT readout by the NuSTAR application-specific integrated circuits. This paves the way for even smaller than 300-μm pixels in the next-generation HREXI detectors. We describe a new HREXI calibration facility (HCF) that enables a high-resolution subpixel-level (100 μm) two-dimensional (2D) scan of a 256-cm2 tiled array of 2 × 2 cm2 CZT detectors illuminated by a bright x-ray AmpTek Mini-X tube source at timescales of around a day. HCF is a significant improvement from the previous apparatus used for scanning these detectors, which took ∼3 weeks to complete a one-dimensional (1D) scan of a similar detector plane. Moreover, HCF has the capability to scan a large tiled array of CZT detectors (32 × 32 cm2) at 100-μm resolution in the 10- to 50-keV energy range, which was not possible previously. We describe the design, construction, and implementation of HCF for the calibration of the P2 detector plane.

Research in Digital Mammography and Tomosynthesis at The University of Toronto

There have been major advances in the field of breast cancer imaging since the early 1970s, both in technological improvements and in the use of the methods of medical physics and image analysis to optimize image quality. The introduction of digital mammography in 2000 provided a marked improvement in imaging of dense breasts. In addition, it became possible to produce tomographic and functional images on modified digital mammography systems. Digital imaging also greatly facilitated the extraction of quantitative information from images. My laboratory has been fortunate in being able to participate in some of these exciting developments. I will highlight some of the areas of our research interest which include modeling of the image formation process, development of high-resolution X-ray detectors for digital mammography and investigating new methods for analyzing image quality. I will also describe our more recent work on developing new applications of digital mammography including tomosynthesis, contrast-enhanced mammography, and measurement of breast density. Finally, I will point to a new area for our research—the application of the techniques of medical imaging to making pathology more quantitative to contribute to use of biomarkers for better characterizing breast cancer and directing therapeutic decisions.

Comparison of High Resolution X-Ray detectors with Conventional FPDs using Experimental MTFs and Apodized Aperture Pixel Design for Reduced Aliasing.

Apodized Aperture Pixel (AAP) design, proposed by Ismailova et. al, is an alternative to the conventional pixel design1. The advantages of AAP processing with a sinc filter in comparison with using other filters include non-degradation of MTF values and elimination of signal and noise aliasing, resulting in an increased performance at higher frequencies, approaching the Nyquist frequency3. If high resolution small field-of-view (FOV) detectors with small pixels used during critical stages of Endovascular Image Guided Interventions (EIGIs) could also be extended to cover a full field-of-view typical of flat panel detectors (FPDs) and made to have larger effective pixels, then methods must be used to preserve the MTF over the frequency range up to the Nyquist frequency of the FPD while minimizing aliasing. In this work, we convolve the experimentally measured MTFs of an Microangiographic Fluoroscope (MAF) detector, (the MAF-CCD with 35μm pixels) and a High Resolution Fluoroscope (HRF) detector (HRF-CMOS50 with 49.5μm pixels) with the AAP filter and show the superiority of the results compared to MTFs resulting from moving average pixel binning and to the MTF of a standard FPD. The effect of using AAP is also shown in the spatial domain, when used to image an infinitely small point object. For detectors in neurovascular interventions, where high resolution is the priority during critical parts of the intervention, but full FOV with larger pixels are needed during less critical parts, AAP design provides an alternative to simple pixel binning while effectively eliminating signal and noise aliasing yet allowing the small FOV high resolution imaging to be maintained during critical parts of the EIGI.

Micro X-ray Fluorescence Imaging in a Tabletop Full Field-X-ray Fluorescence Instrument and in a Full Field-Particle Induced X-ray Emission End Station.

A full field-X-ray camera (FF-XRC) was developed for performing the simultaneous mapping of chemical elements with a high lateral resolution. The device is based on a conventional CCD detector coupled to a straight shaped polycapillary. Samples are illuminated at once with a broad primary beam that can consist of X-rays or charged particles in two different analytical setups. The characteristic photons induced in the samples are guided by the polycapillary to the detector allowing the elemental imaging without the need for scanning. A single photon counting detection operated in a multiframe acquisition mode and a processing algorithm developed for event hitting reconstruction have enabled one to use the CCD as a high energy resolution X-ray detector. A novel software with a graphical user interface (GUI) programmed in Matlab allows full control of the device and the real-time imaging with a region-of-interest (ROI) method. At the end of the measurement, the software produces spectra for each of the pixels in the detector allowing the application of a least-squares fitting with external analytical tools. The FF-XRC is very compact and can be installed in different experimental setups. This work shows the potentialities of the instrument in both a full field-micro X-ray fluorescence (FF-MXRF) tabletop device and in a full field-micro particle induced X-ray emission (FF-MPIXE) end-station operated with an external proton beam. Some examples of applications are given as well.

A high time resolution x-ray diagnostic on the Madison Symmetric Torus.

A new high time resolution x-ray detector has been installed on the Madison Symmetric Torus (MST) to make measurements around sawtooth events. The detector system is comprised of a silicon avalanche photodiode, a 20 ns Gaussian shaping amplifier, and a 500 MHz digitizer with 14-bit sampling resolution. The fast shaping time diminishes the need to restrict the amount of x-ray flux reaching the detector, limiting the system dead-time. With a much higher time resolution than systems currently in use in high temperature plasma physics experiments, this new detector has the versatility to be used in a variety of discharges with varying flux and the ability to study dynamics on both slow and fast time scales. This paper discusses the new fast x-ray detector recently installed on MST and the improved time resolution capabilities compared to the existing soft and hard x-ray diagnostics. In addition to the detector hardware, improvements to the detector calibration and x-ray pulse identification software, such as additional fitting parameters and a more sophisticated fitting routine are discussed. Finally, initial data taken in both high confinement and standard reversed-field pinch plasma discharges are compared.

SU-E-I-53: Comparison of Kerma-Area-Product Between the Micro-Angiographic Fluoroscope (MAF) and a Flat Panel Detector (FPD) as Used in Neuro-Endovascular Procedures

Purpose: To determine the reduction of integral dose to the patient when using the micro-angiographic fluoroscope (MAF) compared to when using the standard flat-panel detector (FPD) for the techniques used during neurointerventional procedures. Methods: The MAF is a small field-of-view, high resolution x-ray detector which captures 1024 × 1024 pixels with an effective pixel size of 35μm and is capable of real-time imaging up to 30 frames per second. The MAF was used in neuro-interventions during those parts of the procedure when high resolution was needed and the FPD was used otherwise. The technique parameters were recorded when each detector was used and the kerma-area-product (KAP) per image frame was determined. KAP values were calculated for seven neuro interventions using premeasured calibration files of output as a function of kVp and beam filtration and included the attenuation of the patient table for the frontal projections to be more representative of integral patient dose. The air kerma at the patient entrance was multiplied by the beam area at that point to obtain the KAP values. The ranges of KAP values per frame were determined for the range of technique parameters used during the clinical procedures. To appreciate the benefit of the higher MAF resolution in the region of interventional activity, DA technique parameters were generally used with the MAF. Results: The lowest and highest values of KAP per frame for the MAF in DA mode were 4 and 50 times lower, respectively, compared to those of the FPD in pulsed fluoroscopy mode. Conclusion: The MAF was used in those parts of the clinical procedures when high resolution and image quality was essential. The integral patient dose as represented by the KAP value was substantially lower when using the MAF than when using the FPD due to the much smaller volume of tissue irradiated. This research was supported in part by Toshiba Medical Systems Corporation and NIH Grant R01EB002873.