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Advanced Materials and Technologies for Radiation Detectors

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Sensor Materials".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 18336

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Dr. Alla Reznik

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Guest Editor

1. Physics Department, Lakehead University, Thunder Bay, ON P7B 5E1, Canada
2. Thunder Bay Regional Health Research Institute, Thunder Bay, ON P7B 6V4, Canada
Interests: advanced materials and technologies for novel X-ray and gamma-ray detectors; solid-state technology for organ-specific positron emission tomography (PET)

Dr. Oleksandr Bubon

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Guest Editor

Thunder Bay Regional Health Research Institute, Thunder Bay, ON P7B 6V4, Canada
Interests: medical imaging detectors; solid state direct conversion and indirect conversion gamma-ray detectors; detector acquisition electronics; coincidence electronic; advanced methods in image reconstruction and coordinate

Special Issue Information

Dear Colleagues,

Radiation detectors are an essential component in modern technology and are widely utilized in security screening and industrial and medical imaging. Currently, innovative photoconductive materials and radiation detector technologies are required to achieve high performance in the sensitivity and spatial and temporal resolution of radiation detectors. As for medical imaging, there is a high demand for materials and technologies that hold a promise to improve diagnostic capabilities at reduced radiation exposures for different medical imaging applications.

This Special Issue of Sensors will be devoted to recent progress in materials and technologies for X-ray and gamma-ray sensing, materials characterization, and their application in radiation detectors and image readout electronics, as well as the development of novel advanced materials for radiation detection. In this Special Issue, we will focus on any relevant radiation sensing technology based on either scintillators or photoconductors, which could advance the field of radiation detection beyond current performance.

It is our pleasure to call for original and review papers within the scope of this Special Issue. Both theoretical and experimental studies are highly welcome. Topics of interest include, but are not limited to, the following:

indirect conversion detectors
direct conversion detectors
novel materials for radiation imaging
perovskite materials
detector readout electronics

Dr. Alla Reznik
Dr. Oleksandr Bubon
Guest Editors

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Keywords

X-ray detectors
photoconductors
scintillators
perovskite
radiation imaging

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Published Papers (7 papers)

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Research

20 pages, 21235 KiB

Open AccessArticle

Development of Adaptive Point-Spread Function Estimation Method in Various Scintillation Detector Thickness for X-ray Imaging

by Bo Kyung Cha, Youngjin Lee and Kyuseok Kim

Sensors 2023, 23(19), 8185; https://doi.org/10.3390/s23198185 - 30 Sep 2023

Cited by 3 | Viewed by 1221

Abstract

An indirect conversion X-ray detector uses a scintillator that utilizes the proportionality of the intensity of incident radiation to the amount of visible light emitted. A thicker scintillator reduces the patient’s dose while decreasing the sharpness. A thin scintillator has an advantage in terms of sharpness; however, its noise component increases. Thus, the proposed method converts the spatial resolution of radiographic images acquired from a normal-thickness scintillation detector into a thin-thickness scintillation detector. Note that noise amplification and artifacts were minimized as much as possible after non-blind deconvolution. To accomplish this, the proposed algorithm estimates the optimal point-spread function (PSF) when the structural similarity index (SSIM) and feature similarity index (FSIM) are the most similar between thick and thin scintillator images. Simulation and experimental results demonstrate the viability of the proposed method. Moreover, the deconvolution images obtained using the proposed scheme show an effective image restoration method in terms of the human visible system compared to that of the traditional PSF measurement technique. Consequently, the proposed method is useful for restoring degraded images using the adaptive PSF while preventing noise amplification and artifacts and is effective in improving the image quality in the present X-ray imaging system. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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18 pages, 3619 KiB

Open AccessArticle

The Effect of Fractionation during the Vacuum Deposition of Stabilized Amorphous Selenium Alloy Photoconductors on the Overall Charge Collection Efficiency

by Safa Kasap

Sensors 2022, 22(19), 7128; https://doi.org/10.3390/s22197128 - 20 Sep 2022

Viewed by 1547

Abstract

The general fabrication process for stabilized amorphous selenium (a-Se) detectors is vacuum deposition. The evaporant alloy is typically selenium alloyed with 0.3–0.5%As to stabilize it against crystallization. During the evaporation, fractionation leads to the formation of a deposited film that is rich in As near the surface and rich in Se near the substrate. The As content is invariably not uniform across the film thickness. This paper examines the effect of non-uniform As content on the charge collection efficiency (CE). The model for the actual CE calculation is based on the generalized CE equation under small signals; it involves the integration of the reciprocal range-field product (the schubweg) and the photogeneration profile. The data for the model input were extracted from the literature on the dependence of charge carrier drift mobilities and lifetimes on the As content in a-Se_1−xAs_x alloys to generate the spatial variation of hole and electron ranges across the photoconductor film. This range variation is then used to calculate the actual CE in the integral equation as a function of the applied field. The carrier ranges corresponding to the average composition in the film are also used in the standard CE equation under uniform ranges to examine whether one can simply use the average As content to calculate the CE. The standard equation is also used with ranges from the spatial average and average inverse. Errors are then compared and quantified from the use of various averages. The particular choice for averaging depends on the polarity of the radiation-receiving electrode and the spatial variation of the carrier ranges. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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16 pages, 3748 KiB

Open AccessArticle

Comparative Analysis of Multilayer Lead Oxide-Based X-ray Detector Prototypes

by Emma Pineau, Oleksandr Grynko, Tristen Thibault, Alexander Alexandrov, Attila Csík, Sándor Kökényesi and Alla Reznik

Sensors 2022, 22(16), 5998; https://doi.org/10.3390/s22165998 - 11 Aug 2022

Cited by 2 | Viewed by 2061

Abstract

Lead oxide (PbO) photoconductors are proposed as X-ray-to-charge transducers for the next generation of direct conversion digital X-ray detectors. Optimized PbO-based detectors have potential for utilization in high-energy and dynamic applications of medical X-ray imaging. Two polymorphs of PbO have been considered so far for imaging applications: polycrystalline lead oxide (poly-PbO) and amorphous lead oxide (a-PbO). Here, we provide the comparative analysis of two PbO-based single-pixel X-ray detector prototypes: one prototype employs only a layer of a-PbO as the photoconductor while the other has a combination of a-PbO and poly-PbO, forming a photoconductive bilayer structure of the same overall thickness as in the first prototype. We characterize the performance of these prototypes in terms of electron–hole creation energy (W_±) and signal lag—major properties that define a material’s suitability for low-dose real-time imaging. The results demonstrate that both X-ray photoconductive structures have an adequate temporal response suitable for real-time X-ray imaging, combined with high intrinsic sensitivity. These results are discussed in the context of structural and morphological properties of PbO to better understand the preparation–fabrication–property relationships of this material. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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20 pages, 8476 KiB

Open AccessArticle

Direct Conversion X-ray Detector with Micron-Scale Pixel Pitch for Edge-Illumination and Propagation-Based X-ray Phase-Contrast Imaging

by Abdollah Pil-Ali, Sahar Adnani, Christopher C. Scott and Karim S. Karim

Sensors 2022, 22(15), 5890; https://doi.org/10.3390/s22155890 - 7 Aug 2022

Cited by 3 | Viewed by 2611

Abstract

In this work, we investigate the potential of employing a direct conversion integration mode X-ray detector with micron-scale pixels in two different X-ray phase-contrast imaging (XPCi) configurations, propagation-based (PB) and edge illumination (EI). Both PB-XPCi and EI-XPCi implementations are evaluated through a wave optics model—numerically simulated in MATLAB—and are compared based on their contrast, edge-enhancement, visibility, and dose efficiency characteristics. The EI-XPCi configuration, in general, demonstrates higher performance compared to PB-XPCi, considering a setup with the same X-ray source and detector. However, absorption masks quality (thickness of X-ray absorption material) and environmental vibration effect are two potential challenges for EI-XPCi employing a detector with micron-scale pixels. Simulation results confirm that the behavior of an EI-XPCi system employing a high-resolution detector is susceptible to its absorption masks thickness and misalignment. This work demonstrates the potential and feasibility of employing a high-resolution direct conversion detector for phase-contrast imaging applications where higher dose efficiency, higher contrast images, and a more compact imaging system are of interest. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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18 pages, 4630 KiB

Open AccessArticle

Dark Current Modeling for a Polyimide—Amorphous Lead Oxide-Based Direct Conversion X-ray Detector

by Tristen Thibault, Oleksandr Grynko, Emma Pineau and Alla Reznik

Sensors 2022, 22(15), 5829; https://doi.org/10.3390/s22155829 - 4 Aug 2022

Cited by 2 | Viewed by 2255

Abstract

The reduction of the dark current (DC) to a tolerable level in amorphous selenium (a-Se) X-ray photoconductors was one of the key factors that led to the successful commercialization of a-Se-based direct conversion flat panel X-ray imagers (FPXIs) and their widespread clinical use. Here, we discuss the origin of DC in another X-ray photoconductive structure that utilizes amorphous lead oxide (a-PbO) as an X-ray-to-charge transducer and polyimide (PI) as a blocking layer. The transient DC in a PI/a-PbO detector is measured at different applied electric fields (5–20 V/μm). The experimental results are used to develop a theoretical model describing the electric field-dependent transient behavior of DC. The results of the DC kinetics modeling show that the DC, shortly after the bias application, is primarily controlled by the injection of holes from the positively biased electrode and gradually decays with time to a steady-state value. DC decays by the overarching mechanism of an electric field redistribution, caused by the accumulation of trapped holes in deep localized states within the bulk of PI. Thermal generation and subsequent multiple-trapping (MT) controlled transport of holes within the a-PbO layer governs the steady-state value at all the applied fields investigated here, except for the largest applied field of 20 V/μm. This suggests that a thicker layer of PI would be more optimal to suppress DC in the PI/a-PbO detector presented here. The model can be used to find an approximate optimal thickness of PI for future iterations of PI/a-PbO detectors without the need for time and labor-intensive experimental trial and error. In addition, we show that accounting for the field-induced charge carrier release from traps, enhanced by charge hopping transitions between the traps, yields an excellent fit between the experimental and simulated results, thus, clarifying the dynamic process of reaching a steady-state occupancy level of the deep localized states in the PI. Practically, the electric field redistribution causes the internal field to increase in magnitude in the a-PbO layer, thus improving charge collection efficiency and temporal performance over time, as confirmed by experimental results. The electric field redistribution can be implemented as a warm-up time for a-PbO-based detectors. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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18 pages, 5443 KiB

Open AccessArticle

Evaluation of a High-Sensitivity Organ-Targeted PET Camera

by Justin Stiles, Brandon Baldassi, Oleksandr Bubon, Harutyun Poladyan, Vivianne Freitas, Anabel Scaranelo, Anna Marie Mulligan, Michael Waterston and Alla Reznik

Sensors 2022, 22(13), 4678; https://doi.org/10.3390/s22134678 - 21 Jun 2022

Cited by 11 | Viewed by 3964

Abstract

The aim of this study is to evaluate the performance of the Radialis organ-targeted positron emission tomography (PET) Camera with standardized tests and through assessment of clinical-imaging results. Sensitivity, count-rate performance, and spatial resolution were evaluated according to the National Electrical Manufacturers Association (NEMA) NU-4 standards, with necessary modifications to accommodate the planar detector design. The detectability of small objects was shown with micro hotspot phantom images. The clinical performance of the camera was also demonstrated through breast cancer images acquired with varying injected doses of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) and qualitatively compared with sample digital full-field mammography, magnetic resonance imaging (MRI), and whole-body (WB) PET images. Micro hotspot phantom sources were visualized down to 1.35 mm-diameter rods. Spatial resolution was calculated to be 2.3 ± 0.1 mm for the in-plane resolution and 6.8 ± 0.1 mm for the cross-plane resolution using maximum likelihood expectation maximization (MLEM) reconstruction. The system peak noise equivalent count rate was 17.8 kcps at a ¹⁸F-FDG concentration of 10.5 kBq/mL. System scatter fraction was 24%. The overall efficiency at the peak noise equivalent count rate was 5400 cps/MBq. The maximum axial sensitivity achieved was 3.5%, with an average system sensitivity of 2.4%. Selected results from clinical trials demonstrate capability of imaging lesions at the chest wall and identifying false-negative X-ray findings and false-positive MRI findings, even at up to a 10-fold dose reduction in comparison with standard ¹⁸F-FDG doses (i.e., at 37 MBq or 1 mCi). The evaluation of the organ-targeted Radialis PET Camera indicates that it is a promising technology for high-image-quality, low-dose PET imaging. High-efficiency radiotracer detection also opens an opportunity to reduce administered doses of radiopharmaceuticals and, therefore, patient exposure to radiation. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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12 pages, 9397 KiB

Open AccessArticle

Usefulness of an Additional Filter Created Using 3D Printing for Whole-Body X-ray Imaging with a Long-Length Detector

by Hyunsoo Seo, Wooyoung Kim, Bongju Han, Huimin Jang, Myeong Seong Yoon and Youngjin Lee

Sensors 2022, 22(11), 4299; https://doi.org/10.3390/s22114299 - 6 Jun 2022

Cited by 1 | Viewed by 2883

Abstract

We recently developed a long-length detector that combines three detectors and successfully acquires whole-body X-ray images. Although the developed detector system can efficiently acquire whole-body images in a short time, it may show problems with diagnostic performance in some areas owing to the use of high-energy X-rays during whole-spine and long-length examinations. In particular, during examinations of relatively thin bones, such as ankles, with a long-length detector, the image quality deteriorates because of an increase in X-ray transmission. An additional filter is primarily used to address this limitation, but this approach imposes a higher load on the X-ray tube to compensate for reductions in the radiation dose and the problem of high manufacturing costs. Thus, in this study, a newly designed additional filter was fabricated using 3D printing technology to improve the applicability of the long-length detector. Whole-spine anterior–posterior (AP), lateral, and long-leg AP X-ray examinations were performed using 3D-printed additional filters composed of 14 mm thick aluminum (Al) or 14 mm thick Al + 1 mm thick copper (Cu) composite material. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and radiation dose for the acquired X-ray images were evaluated to demonstrate the usefulness of the filters. Under all X-ray inspection conditions, the most effective data were obtained when the composite additional filter based on a 14 mm thick Al + 1 mm thick Cu material was used. We confirmed that an SNR improvement of up to 46%, CNR improvement of 37%, and radiation dose reduction of 90% could be achieved in the X-ray images obtained using the composite additional filter in comparison to the images obtained with no filter. The results proved that the additional filter made with a 3D printer was effective in improving image quality and reducing the radiation dose for X-ray images obtained using a long-length detector. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Radiation Detectors)

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