24th International Workshop on Radiation Imaging Detectors (2024)

Traditional X-ray scanning systems for cargo use ionising radiation which can be harmful to operators and the environment and requires shielding. Fully passive muon tomography is a promising alternative or a complementary approach to X-ray scanners. Muon tomography is a non-invasive technique that uses naturally occurring cosmic-ray muons and their scattering in various materials to create images of cargo in trucks or containers without applying ionising radiation. Muons are high-energy particles that are produced when primary cosmic rays collide with the Earth's atmosphere. These muons can penetrate through thick materials, such as concrete or metal, and are therefore useful for detecting hidden objects, including contraband. Muon tomography is expected to be used for detection of a wide range of materials, including metals, plastics, and organic materials like drugs or cigarettes, as well as weapons and explosives. In this work we have used the GEANT4 toolkit to simulate the performance of muon tomography in identifying the contraband cigarettes hidden inside the legal low-Z materials in a truck trailer. We have used the Point of Closest Approach (PoCA) reconstruction algorithm to reconstruct the three-dimensional image of a loaded truck. As an example we have considered cigarettes hidden among wood pellets, plasterboards and wood planks. In all investigated scenarios cigarettes were detected and localised. We have applied CRY and MUSIBO muon generators to sample cosmic-ray muons at the surface of the Earth. The CRY software package generates muons on a horizontal plane while MUSIBO, based on a well-known Gaisser’s parameterisation of the muon spectrum and angular distribution, modified to account for muon decay and Earth surface curvature, generates muons on the surfaces of a box (rectangular parallelepiped) which is more appropriate for simulation of inclined muons. This simulation study using GEANT4 and relatively simple but reliable PoCA reconstruction algorithm demonstrates the potential of muon tomography for detecting hidden materials in cargo. We conclude that muon tomography is capable of producing detailed images of various objects and can become a powerful tool for detecting contraband cigarettes and other goods in a non-invasive and harmless way.

Speaker: Anzori Georgadze (Institute of Physics, University of Tartu)

Speaker: Bohumir Zatko

Speaker: Mattias Simons (Hasselt University)

RIPTIDE is a new detector concept aiming to track fast neutrons. It is based on neutron-proton elastic collisions inside a plastic scintillator, where the neutron momentum can be measured by imaging the scintillation light [1-3]. More in detail, by stereoscopically imaging the recoil-proton tracks, the proposed apparatus provides neutron spectrometry capability, and enable the online analysis of the specific energy loss along the track (see Fig. 1). In principle, the spatial and topological event reconstruction enables particle discrimination, which is a crucial property for neutron detectors.
In this contribution, we report the advances on the RIPTIDE detector concept. In particular, we have developped a Geant4 optical simulation to demonstrate the possibility of reconstructing with sufficient precision the tracks and the vertices of neutron interactions inside a plastic scintillator. To realistically model the optics of the scintillation detector, monoenergetic protons were generated inside a 6x6x6 cm3 cubic BC408 scintillator, and the ensuing optical photons were recorded on a scoring plane corresponding to the surfaces of the cube. The photons were then trasported throug an optical system to a 2x2 cm2 photo sensitive area with 1 Megapixel. The first panel of Fig. 1 show an example of one of the 6 projections of a track on a pixellated photosensor.
Moreover, we have developed 2 different analysis procedures to reconstruct 3D tracks: one based on least square fitting and one on Principal Component Analisys. The main results of this study will be presented with a particular focus on the role of the optic system and the attainable spatial/energy resolution.
[1] A. Musumarra et al 2021 JINST 16 C12013
[2] C. Massimi et al 2022 JINST 17 C09026
[3] P. Console Camprini et al 2023 JINST 18 C01054

Speakers: Agatino Musumarra (INFN-Sezione di Catania (IT)), Patrizio Console Camprini (ENEA (IT))

X-Ray imaging techniques at synchrotron facilities often rely on hybrid pixel detectors. They consist of photon-counting devices encompassing a photo-active semiconductor sensor integrated with a pulse processing Application Specific Integrated Circuit (ASIC) capable of performing input pulse counting along a pixelated array of discrete 55 x 55 µm counting units. Recently, our group published an initial set of characterization experiments on the PIMEGA detectors, which were developed and employed at the Brazilian Synchrotron Facility [1]. Our previous work focused on the physical responses of 300 µm thick silicon sensors integrated into Medipix3RX ASICs. In this report, we compare the physical responses of 300 and 675 µm thick silicon-based detectors. Among the experiments gathered within this contribution, we have performed the slanted edge technique for measuring the Modulation Transfer Function (MTF) [2,3]. This measurement was employed for assessing the thickness dependence of the detector’s spatial resolution, and its results are depicted in Figure 1. This experiment was conducted under 5.9 keV incident energy (E0), for equivalent energy threshold values of 0.5 and 0.7 E0. Our work demonstrates that, even though thicker sensors present higher absorption efficiencies, their MTF values are lower along the entire spatial frequency domain. Moreover, higher threshold settings yield larger MTF values for both probed thicknesses. These observations are a consequence of the charge diffusion lengths within the thickness of the semiconductors, which lead to more pronounced charge-sharing effects on thicker sensors. Our results suggest a compromise between sensor absorption efficiency and spatial resolution. Future characterization experiments will also be employed to fully describe the thickness dependence of the detector's physical outputs.

Speaker: Raul Back Campanelli

Gastrointestinal (GI) foreign bodies occur when pets consume items that are nondigestible and will not readily pass through their stomach or intestines. Traditional radiography has been widely used to detect GI foreign bodies in pets. However, particularly, detecting low-density GI foreign bodies such as wood, plastic, clothing, and sticks is often difficult in conventional absorption-based radiography. In this study, to overcome this difficulty, we propose a novel imaging method, the so-called single grid-based dark-field X-ray imaging (SG-DFXI), for more clearly detecting low-density foreign bodies in pets. SG-DFXI is a single-exposure, non-interferometric imaging method for retrieval of absorption and dark-field images using a conventional X-ray grid. To demonstrate the efficacy of the proposed method, an experiment was conducted with a mouse phantom containing a piece of wooden chopstick. The preliminary results of an absorption and a dark-field images of a mouse phantom that contained a piece of wooden chopstick. According to our preliminary results, the proposed approach significantly improved the ability to detect low-density foreign bodies in pets.

Speaker: Mr Jonghyeok Lee (Yonsei university)

Medical linear accelerators are used to treat patients by irradiating X-rays and electron beams. Electron beams deliver most of their energy to the skin surface due to their short range. Radiation therapy uses these characteristics to treat superficial tumors such as skin cancer, breast cancer, and head and neck cancer. Since accurate dose delivery is required for such electron beam treatment, quality classification (QA) of electron beam must be performed regularly.
However, in clinical electron beam QA, it is recommended to cross-calibrate the Plane-parallel ionization chamber using the absorbed dose to water correction factor of the cylindrical ionization chambers to improve the accuracy in high-energy electron beam measurement. This complicates the measurement.
Therefore, in this study, a relative QA dosimeter for electron beams that can measure low and high energy electron beams without cross-calibration was developed by using CsPbBr3 material with excellent high-energy radiation detection efficiency. In addition, the detection performance was evaluated by analyzing the electrical response characteristics.
The CsPbBr3 dosimeter was manufactured as a unit cell type polycrystalline dosimeter. Electrical response characteristics were measured at energies of 6, 9 and 12 MeV, and reproducibility, linearity, and PDD were analyzed and evaluated by irradiating the dosimeter with a radiation dose of 100 MU at 500 MU/min.
In the reproducibility evaluation, the relative standard deviation (RSD) at 6, 9 and 12 MeV was analyzed to be 1.06%, 1.39% and 1.49%, respectively. In the linearity evaluation result, the coefficient of determination according to the linear regression analysis was analyzed to be 0.9997, 0.9997 and 0.9993 at 6, 9 and 12 MeV, respectively. The PDD evaluation was shown to show the correct Dmax point. As a result of the evaluation, the manufactured CsPbBr3 dosimeter was evaluated to have suitable performance for application as a dosimeter in various energy bands of 6 MeV, 9 MeV and 12 MeV.
As a future study, if a large-area flat-panel dosimeter is manufactured by analyzing the dependence characteristics according to the dosimeter area and field size, QA of electron beam treatment will be possible with a more simplified procedure. This is a basic study of the development of the electron beam QA dosimeter, indicating the potential use.

Speaker: Mr Seung-woo Yang (Department of Radiation Oncology, Collage of Medicine, Inje University, Republic of Korea)

Since Roentgen's discovery of X-rays, anode angulation technique has been widely used in medical X-ray tubes to reduce the focal spot size and transmit sufficient X-rays through the anode. Unfortunately, this technique inevitably produces the so-called shift-variant image blur that causes the focal spot to have a different shape, depending on the position of the detector plane [1, 2]. This effect becomes more pronounced as the distance from the center of the detector plane (or the source magnification) increases. However, it is neglected in traditional radiography because isolating and analyzing this effect from other effects, such as scattered X-rays produced through the object and detector-induced blur, are often difficult. The purpose of this study is to characterize the effect of the shift-variant focal spot blur on the image quality as a function of detector position with various X-ray imaging parameters in radiography, including magnification, focal spot size, and so on. Figure 1 shows the schematics of (a) an X-ray imaging geometry and (b) the formation of X-ray image of an ideal point object, depending on the direction of the finite focal spot of the X-ray tube. We used a simple model of the focal spot that decomposes it into three independent components. According to this model, shift-invariant image blur can be caused by the x and y-components (FSx and FSy) perpendicular to the beam direction; shift-variant image blur by the z-component (FSz) parallel to the central beam direction. To validate the efficacy of the proposed method, we conducted a Monte Carlo simulation and an experiment using an X-ray imaging system that consisted of an X-ray tube with a focal spot size of 3 mm and a CMOS detector with a pixel size of 0.14 mm and an active area of 460 × 460 mm2. Figure 2 shows the geometry of an X-ray imaging system used in the Monte Carlo simulation and the X-ray imaging system used in the experiment. Figure 3 shows the MTF curves measured at the center (i.e., beam angle = 0) and periphery (beam angle = 10) of the detector for three different object magnifications of M = 1.00, 1.27, and 2.00. Our preliminary results showed that nonnegligible shift-variant image blur occurred especially when an X-ray tube with a large focal spot and a detector with a large area are used in radiography. More quantitative simulation and experimental results will be presented in the paper.

Speaker: Hunwoo Lee (Yonsei University)

Chest radiography is the most routinely used X-ray imaging technique for screening and diagnosing lung and chest diseases, such as lung cancer and pneumonia. However, the clinical interpretation of the hidden and obscured anatomy in chest X-ray images remains challenging because of the bony structures overlapping the lung area. Thus, multi-perspective imaging with a high radiation dose is often required. In this study, to address this problem, we propose a deep learning-based soft-tissue decomposition method using fast fuzzy C-means (FCM) clustering with computed tomography (CT) dataset (Fig. 1). In this method, FCM clustering is used to decompose a CT dataset into bone and soft-tissue components, which are synthesized into digitally reconstructed radiographs (DRRs) to obtain large amounts of X-ray decomposition datasets as ground truths for training. In the training stage, chest DRRs and soft-tissue DRRs are used as input and label data, respectively, for training the network. During testing, a chest X-ray image is fed to the trained network to output the corresponding soft-tissue image component. To verify the efficacy of the proposed method, we conducted a feasibility study on clinical chest CT data from the AAPM Lung CT Challenge. Figure 2 shows the decomposed bone and soft-tissue components of the original CT image using the fast FCM and their synthesized DRRs. Figure 3 shows two cases of soft-tissue decomposition obtained using the proposed method and the measurements of the structural similarity index metric (SSIM). Consequently, the findings of our feasibility study indicate that the proposed method can offer a promising outcome for this purpose. More quantitative results will be presented in the paper.

Speaker: Mr DUHEE JEON (Yonsei university)

Speaker: Ms Selina Ringsborg Howalt Owe (Technical University of Denmark)

In the industrial sector, commonly used non-destructive testing techniques include ultrasonic testing (UT), radiographic testing (RT), penetration testing (PT), magnetic testing (MT), and other methods. These techniques have undergone significant development, particularly in real-time testing, low cost, high efficiency, and high precision, with the concomitant development and release of novel industrial products. Moreover, these techniques are being integrated with artificial intelligence to enhance product reliability.
Several research studies have attempted to apply computed tomography (CT) technology, commonly employed in the medical industry, to the industrial sector by incorporating it into the RT testing method. This enables easy detection of internal product defects, although its application is limited by system size and cost.
The increasing adoption of additive manufacturing (AM), which employs 3D printing technology, in the manufacturing industry has further emphasized the need for non-destructive testing. AM products necessitate precision analysis through 3D cross-sectional images of material layers, and non-destructive testing using CT methods within RT is becoming an increasingly valuable testing technique. Therefore, this study applied CT non-destructive testing to in-house AM products to ensure their reliability and confirmed the applicability of CT testing to AM products by varying testing parameters.

Speaker: hunhee kim (Doosan Enerbility)

Scintillation materials can convert high-energy rays into visible light. Generally, solid scintillator can be divided into crystal scintillator, plastic scintillator, glass scintillator and ceramic scintillator. Compared with crystal scintillator, the glass scintillator has many advantages, such as a simple preparation process, low cost and continuously adjustable components. Therefore, glass scintillator has long been conceived for application in the nuclear detection such as hadron calorimeters, the HCAL of CEPC. In 2021, the researchers in the Institute of High Energy Physics (IHEP) have set up the Large Area Glass Scintillator Collaboration (GS group) to study the new glass scintillator with high density and high light yield. Currently, a series of high density and high yield scintillation glasses have been successfully developed. The maximum density of the glass can exceed 6.9 g/cm3. And the maximum light yield can reach up 3400 ph/MeV. Moreover, Ce3+-doped borosilicate glass can balance the targets of high density and high light yield. In addition, the glasses can achieve neutron/gamma dual detection due to presence of Li, B and Gd element.

Speaker: Sen Qian

Radiations in the terahertz and infrared spectrum have proven useful in practical applications such as security screening, medical imaging, and wireless communication [1,2,3]. Many of these applications would greatly benefit from practical and compact detectors capable of working at room temperature, capturing tens of images per second and providing a low-medium number of pixels (typically around 104 - 105 pixels). In order to fulfill all these requirements in the frequency range of 0.3-10 THz, where classic electronic devices are highly inefficient, we make use of Si3N4 micro-bolometers which shift their mechanical resonance frequency as they heat-up by absorbing terahertz radiation.
In previous works, the vibration of these devices was induced by a piezo membrane, while the resonance frequencies were determined through optical interferometry [4]. However, in our latest sensors (as shown in Figure 1), we have implemented a novel approach that greatly simplifies the excitation and measurement of the sensor's resonance frequency. Specifically, two golden stripes are integrated into the device, and under appropriate conditions, current injected through one of these stripes can vibrate the sensor, inducing a modulated current on the other strip for electrical readout, whose frequency is a function of the absorbed radiation.
In the presented work, we describe the setup used to perform a fully electrical readout of these sensors (Figure 2), which not only simplifies the measurement process but also provides a significant improvement in measurement speed and accuracy. We thoroughly discuss the first measurements obtained using this setup and compare them with both the interferometry results and our previous simulations, where we have modelled a sensor with a lumped parameter passband filter [5]. Our results demonstrate the efficacy of this approach for real-time terahertz imaging and other applications where fast and accurate measurements are critical.

Speakers: Mr Leonardo Gregorat (DIA, University of Trieste, 34127 Trieste, Italy), Mr Marco Cautero (DIA, University of Trieste, 34127 Trieste, Italy)

Speaker: Dr Pavel Broulim (University of West Bohemia (CZ))

Speaker: Dr Johannes Müller-Seidlitz (Max Planck Institute for Extraterrestrial Physics)

We have development alpha dust monitor with a red or infrared emitting scintillators, and the scintillation properties were investigated for Ce:Y₃(Mg_x Al_5-2x Si_x)O₁₂ (x=0.0, 0.5, 2.0) crystals were grown by the micro-pulling-down method.Ce-doped Y₃(Mg₂ Al Si₂)O₁₂ had an emission wavelength of 620 nm, and the red-shift of emission bands was observed for Mg and Si-admixed samples due to changing lattice constants compared to the Mg and Si free sample.

Speaker: Shunsuke Kurosawa (Tohoku Univ. & Osaka Univ.)

Speaker: Petr Burian (Czech Technical University in Prague (CZ))

Neutron radiation effects on semiconductor detectors have long been investigated, as it offers a more complete understanding of the amount of damage to which such sensors can be subjected while operating them under extreme experimental conditions. The competition between ionizing (IEL) and non-ionizing energy losses (NIEL) was described theoretically through partition functions, which are in a fair degree of agreement with silicon sensor experimental observations and prompt the need for extending the studies to other materials which are used for radiation detection, like gallium arsenide(GaAs) and cadmium telluride(CdTe).The pixelation of Timepix3 detectors together with the energy deposition measurement and pattern discrimination algorithms which are exploited for separating the different neutron interactions (elastic and inelastic). In order to measure the competition of IEL and NIEL in different semiconductors with unprecedented accuracy, an experiment was performed at the Weapon Neutron Research facility in the Los Alamos Neutron Science Centre, where several Timepix3 sensors were placed in a neutron radiation field of an energy spectrum ranging from hundreds of keV to hundreds of MeV. The presentation aims to deliver a comprehensive look at the analysis process leading to new results on the competition between IELs and NIELs of recoil nuclei in several semiconductor lattices following fast neutron interactions with Timepix3 sensors.

Speaker: Radu-Emanuel Mihai (Institute of Experimental and Applied Physics, Czech Technical University in Prague)

Nuclear medicine imaging is an important non-invasive technique in medical care for obtaining information inside the body by detecting radiation emitted from within the body to the outside and visualizing its distribution. In this study, we developed a new nuclear medicine imaging technique that combines magnetic field and RI imaging by utilizing the characteristic that the emission angle of gamma rays changes due to the influence of external fields such as magnetic and electric fields in the intermediate state of cascade nuclear decay and measuring angle correlation. We also conducted exploration and quantification of medical RI tracers that are more susceptible to perturbations by external fields.

Speaker: Mr Boyu Feng (The University of Tokyo)

Speaker: Kirsty Paton (Paul Scherrer Institut)

p-terphenyl crystals were grown by the self-seeding vertical Bridgman technique, and its scintillation properties were investigated for fast neutron scintillator applied in high temperature condition around 400K. light outputs were approximately 9,000 photons/(5.5-MeV alpha) and 19,000 photons/MeV for alpha-ray and gamma-ray excitation, respectively. we embedded a p-terphenyl pixel scintillation array and succeeded in imaging irradiated with fast neutrons with a multi-anode photomultiplier tube.

Speaker: Shunsuke Kurosawa (Tohoku Univ. & Osaka Univ.)

Radiation monitor is an important technique for the decommissioning of the f*ckushima Daiichi Nuclear Power Plant (FDNPP) with safety, and the internal exposure of workers who inhale alpha-emitting dust, such as plutonium dioxide particles, in nuclear facilities is a crucial matter for human protection from radiation. Detailed information on the radiation dose distribution and alpha-emitting dust inside the nuclear reactor is necessary to operate the decommissioning of FDNPP. Thus, we have developed an alpha-ray imaging detector with high positional resolution consisting of a scintillation sheet, optical microscope and Complementary Metal Oxide Semiconductor (CMOS) camera (ORCA-Flash4.0 V3, Hamamatsu).
To obtain the high-resolution imaging, high-light output scintillator is required, and Cs3Cu2I5 (CCI) was selected as the scintillator for the alpha detector in this time owing to a high light output of 41,500 photon/MeV. Moreover, this material has been applied to high-resolution X-ray imaging techniques. In this paper, we show the feasibility study on the application of the CCI scintillator for alpha-ray imaging.

Speaker: Mr Yusuke Urano (Graduate School of Engineering, Tohoku University)

This work presents SpacePix3, an improved version of the SpacePix2 ASIC [1]. It is a novel MAPS sensor developed for soft advanced space dosimetry fabricated in a 180 nm PDSoI CMOS process. The sensitive area is a matrix of 64×64 pixels with a 60 μm pitch. The detection diode is integrated in a handle wafer, with the depletion depth of approximately 35 μm at -150 V bias. The signal is digitised by 32 column ADCs with 10 bit resolution. The effective dynamic range of the pixel front-end amplifier is 5 to 65 ke−, with the possibility of backside pulse digitization of signal 0.25 to 30 Me−. The first measurement results using nuclide sources and accelerator ion beams are presented.
This ASIC is suitable for the proposed Czech lunar mission, where it will be exposed to ionising radiation ranging from electrons and protons in the van Allen belts to the heavy ions in the galactic cosmic rays. Therefore, its survivability and response to the TID irradiation was tested according to the relevant standards such as ESCC Basic Specification No. 22900
up to a total dose of 5 kGy in semilogarithmic steps. Results of power consumption and detection response to 238Pu X-ray photons were evaluated before and after irradiation.

Speaker: Maria Marcisovska (Czech Technical University in Prague (CZ))

We present preliminary results of a novel submarine gamma imager (SUGI) based on pixelated CdZnTe detector modules. The instrument, mounted on a remotely operated vehicle (ROV), has been tested in a series of field deployments performed at the hydrothermal fields of the island of Milos, Greece. The analysis of the collected data demonstrate the capabilities of the instrument being developed, while comparison with a reference gamma detector confirms the validity of the results.

Speaker: Dr Valsamis Ntouskos (National Technical University of Athens)

With an incidence of 1 - 4 per 100,000 habitants in the western world, glioblastoma is the most common primary malignant brain tumour [1]. Significant advances have been made in our understanding of the pathophysiology of glioblastoma over the past decade, however, glioblastoma remains an incurable disease with a median survival time after diagnosis of approximately 15 months [2]. Moreover, therapies that have had better results in other types of cancer were ineffective in glioblastoma. In order to combat this disease new therapeutic modalities are needed to develop truly effective treatments. One approach is based on the use of genetically modified cells, in particular human mesenchymal stem cells (hMSC). It could be shown that hMSCs have the ability to selectively migrate to glioblastoma tumours in animal models, suggesting their potential for engineered cell glioblastoma therapy [3,4]. hMSCs can be isolated from different tissues, including bone marrow and adipose tissue, the latter being a very accessible and abundant source. Therefor each potential patient can be their own donator of hMSCs. It was demonstrated [3] that GNP loaded hMSCs injected into the carotid artery of nude mice migrated towards and integrated into U87 glioma tumours present in mice. Moreover, hMSCs can be permanently labelled with gold nano particles (GNP) as described in [5] constituting thus a selective marker, which subsequently can be detected utilizing X-rays imaging modalities. Here we report on the explorative implementation of spectral X-ray computer tomography (CT) in combination with GNPs as a permanent cell marker for hMSCs for investigating micrometric tumour cell distribution in rodents. Preliminary experiments have been carried out at the PEPI lab [6] utilizing a CdTe hybrid pixel detector [7] with a pixel size of 62 µm x 62 µm. We were able to obtain post mortem high-resolution 3D spectral images (figure1) of mice bearing U87 glioma tumours, which prior scarification had been injected with GNP loaded hMSCs. In this contribution we will present first encouraging results of this promising imaging technique, which could significantly improve the understanding of complex processes of disease progression and the effects of therapies in preclinical trials.

Speaker: Prof. Ralf Hendrik Menk (Elettra Sincrotrone Trieste)

Speckle-based imaging (SBI) is a multi-modal X-ray technique that gives access to attenuation, phase-contrast, and dark-field signals. The signal retrieval with the Unified Modulated Pattern Analysis (UMPA) algorithm is based on the modulation of a reference speckle pattern generated from a sandpaper when a sample is inserted in the beam. By stepping the diffuser or the sample transversely to the beam direction, it is possible get a better convergence of the model. Here, we show how a continuous helical acquisition can extend the detector's field-of-view and speed up the acquisition while maintaining a multi-frame approach for the signal retrieval of a test object.

Speaker: Sara Savatović (Department of Physics, University of Trieste, Via Valerio 2, 34127 Trieste, Italy; Elettra-Sincrotrone Trieste, Strada Statale 14 – km 163.5, 34149 Basovizza, Italy)

Photon-counting technology matured enough to be implemented in clinical computed tomography (CT) scanners with the potential to revolutionize clinical practice due to low imaging noise, uniform spectral weighting, and inherent spectral separation. Photon fluxes in clinical CT can reach up to $10^{8}$ counts mm$^{-2}$s$^{-1}$, imposing significant technical challenges on the counting speed of photon-counting detectors [1]. Pulse pileup is the effect in which two or more photons impinging the same detector pixel are processed as a single event, leading to counting loss and spectral distortion of the signal. In clinical CT, the conditions for pulse pileup to occur are usually met at high tube currents and can be observed inside the lungs or at the edges of the patient’s body. Spectral distortions also have a significant impact on quantitative imaging tasks such as iodine quantification and virtual monochromatic imaging. An effect occurring independently of photon flux is charge sharing due to fluorescence effects and the spreading of a charge cloud, causing multiple counts at lower energies and blurring of the image. Pulse pileup and charge sharing contradict each other to some extent because i) larger pixel sizes reduce charge sharing between pixels while increasing the probability for pulse pileup and ii) faster ASIC helps distinguish single photons in high-flux conditions while reasonably slower detectors allow for integration of split charges created due to the charge sharing. Thus, hardware-based methods are often implemented to correct for one or both effects depending on the detector design and intended application.
In this work, we investigated the potential of instant-retrigger technology developed by DECTRIS Ltd. to improve non-paralyzable detectors in high-flux conditions [2]. Instant retrigger technology re-evaluates the pulse signal after a predetermined deadtime interval after each count and potentially retriggers the counting circuit in case of pulse pileup. The respective deadtime interval is adjustable and accounts for the width of a single photon pulse. The instant-retrigger analytical model was developed and implemented inside the DukeSim CT simulator to generate realistic CT simulations of the XCAT chest [3] phantom containing iodine contrast. DukeSim contains primary ray-tracing and Monte Carlo scattering models, realistic models of CT geometries, and a model of a photon-counting detector including charge sharing model and paralyzable and non-paralyzable detector configurations [4]. For this work, we used a 1.6 mm thick CdTe sensor bulk and 0.5x0.5 mm detector pixel size. The instant-retrigger analytical model [5] was applied after charge sharing and compared against the other two models for the task of material decomposition. Material decomposition is described as:
$\mu(E) = \mu_{1}(E)\,x_{1} + \mu_{2}(E)\,x_{2}$
where $\mu_{1}(E)$ and $\mu_{2}(E)$ are known linear attenuation coefficients of basis materials (e.g., soft tissue and bone), $x_{1}$ and $x_{2}$ are energy-independent coefficients (in 2D called basis images/maps), and $\mu(E)$ is the measured value for each voxel. The basis images, which represent the equivalent concentrations of basis materials for each voxel, encode the quantitative information about the voxel composition. Figure 1 shows how the retriggering mechanism improves spectral information in high flux conditions in comparison with slightly slower non-paralyzable and paralyzable detectors. Figure 2 shows decomposed soft tissue and bone maps of the virtual XCAT phantom obtained using the simulation without modeling the pulse pileup effect. Figure 3 shows how the accuracy of material decomposition depends on the retrigger time.
Faster retriggering time improves spectral response and maintains accurate material decomposition in spectral CT. Although retriggering times of 15 ns are achievable with current detectors, more accurate analytical models accounting for variable pulse lengths generated by polychromatic sources might be needed to determine optimal values.
[1] M Danielsson et al Phys Med Biol. (2021), 66(3):03TR01.
[2] T Loeliger et al IEEE NSS/MIC (2012), p. 610–5.
[3] WP Segars et al 4D Med Phys. (2010), 37(9):4902–15.
[4] E Abadi et al IEEE Trans Med Imaging. (2019), 38(6):1457–65.
[5] P Zambon et al, Dectris Ltd., Manuscript in preparation (2023)

Speaker: Stevan Vrbaski

In the field of security and defense, the detection of special nuclear materials and other radioactive materials requires the use of neutron and gamma-ray detection systems. Silicon photomultipliers have been employed in these detectors due to their advantages of being lightweight, compact, and low power consuming. Accurate identification of neutron and gamma-ray pulses from these detectors plays a crucial role in the reliability of radiation measurements. To improve the discrimination of pulse shapes, various pulse shape discrimination techniques have been studied, developed, and applied. In this research, a minimal neural network artificial intelligence (AI) configuration was designed to correspond to the identification characteristics of neutron and gamma-ray pulses obtained from an EJ-200 scintillation detector. The principle of minimum error was applied in the design, so that despite the minimal configuration, the accuracy of the identification results was not compromised. Experiments showed that with this design, AI achieved higher accuracy in identification compared to the pulse shape integration method. Monte Carlo simulations were validated by laboratory measurements and field tests were performed using real gamma-ray and neutron sources. Detection and localization within one meter were achieved using a maximum likelihood estimation algorithm for ¹³⁷Cs sources (4 MBq), as well as the detection of ²⁴¹Am–Beryllium (1.45 GBq) source placed inside the shipping container. For the measured pulses from a ⁶⁰Co source, the AI-based MNRNT accurately identified 97.90% of the pulses in the energy range of 50-2000 keVee (keV electron equivalent), and achieved 96.80% accuracy for pulses in the low energy range of 50-150 keVee. These results demonstrate that artificial intelligence methods can be applied to improve the identification and analysis of radiation events even with small-scale radiation detectors.
Keywords: Pulse shape discrimination, AI, neutron detection, scintillation detector.

Speaker: Dr Sy Minh Tuan HOANG (Thu Dau Mot University)

Dedicated to the control of radiation on industrial, research and civil sites, the portal monitors produced by Bertin Technologies, automatically detects radioactive source carried by trucks, cars, and trains. An
alarm classification can discriminate natural and artificial radiation.
The research and development division is working on the detection at low energy, where the performances of the detector needs to be improved. Energy-weighted algorithm is applied at low energy to reduce
the false alarm and detect the 226Ra radioelement. Preliminary experimental analysis and simulation on Geant4 are presented and discussed.

Speaker: Mrs Celia LEY (Bertin Technologies, Nuclear detection R&D)

Speaker: Riley Reid (University of Colorado Boulder)

Speaker: Renata Longo (UNIVERSITY OF TRIESTE & INFN)

Speaker: Daniel Vavrik

We present the development of a neutron and gamma ray spectrometer for possible use in terrestrial and planetary science. The spectrometer module is called the Cosmogenic Neutron Detector (CosmoNeD) and is based on a monolithic scintillator with a silicon photomultiplier (SiPM) array and an integrated readout electronics. The prototype is under development and evaluation for small neutron spectrometers for terrestrial and space applications and will detect neutrons with energies of 0.025 eV – 1 MeV with energy resolution of 4% at 662 keV (Cs) with the capability of distinguishing gamma-rays in the same range. It has the objective to measure the abundance of hydrogen bearing compounds and some rock-forming elements in the soil for moisture measurements and planetary geology studies. The preliminary results regarding its performance with various gamma-ray sources are presented here.

Speaker: Deniz Ölçek (CENSSS, IDEAS)

Monitoring and characterization of accelerator particle beams is necessary for operation of the facilities and their use in a broad range of applications from basic research (nuclear and high-energy physics) to applied research such as particle radiotherapy. Particle beams are typically produced in high beam intensities (> nAmp) which can be directly monitored by current-integrating devices and gas-based detectors. Conventional beam monitors provide namely the total beam current intensity and time profile with limited information on beam composition, beam size and directionality (beam divergence). When the beam intensity can be significantly decreased, detailed and more complete information can be provided by placing a high-resolution imaging detector directly on the beam path. Detailed information on the beam can be thus directly measured with hybrid semiconductor pixel detectors of the Timepix family [1]. For high-intensity beams however, positioning the detector on the beam path is no longer feasible. For this purpose, we make use of a scattering foil and detect the scattered beam particles behind the target and away from the beam axis – see Fig. 1b. A high-density thin foil (Ta, < 1 mm thick) is chosen for optimal yield of Rutherford scattering. We use a Timepix3 detector operated in compact electronics MiniPIX Timepix3 (Fig. 1a) [2] for directional- and energy-sensitive tracking of the scattered particles (Fig. 1c) [3]. Experiments were performed with proton beams of intensity in the nAmp range at the light ion cyclotron U 120M of the NPI Prague (33 MeV) and at a cyclotron Proteus 235 at the PTC Prague (100 and 226 MeV). We tested various beam settings in terms of beam energy, intensity, beam size, distance, and geometry. Tilting the detector-sensor plane to the direction of the particles increases the spectral-tracking resolution. Pattern recognition analysis of the pixelated tracks of single particles enables to reconstruct the trajectory of the scattered particles in wide (2π) field-of-view (FoV) without the need for collimators and with particle-type resolving power and high discrimination of background [4]. At the detector position Timepix3 registers the spatial and also the directional distribution of scattered protons (Fig. 2). The angular resolution for heavy charged particles and protons is around 10º along the elevation direction and around 2º along the sensor plane (azimuth angle) [3]. The particle beam can be imaged along the beam axis at the foil position by back-projection reconstruction (will be presented). Results provide multiple-parametric information on the primary beam in terms of particle flux, beam size (limited resolution), time dependence and spectral distribution. We extrapolate the detector results and derive information on the primary beam intensity by dedicated Monte-Carlo simulations using MCNP6.2 [5].

Speaker: Dušan Poklop

Semi-monolithic crystals have the potential of combining the timing capabilities of pixelated crystals and the 3D positioning of monolithic crystals. These crystals are monolithic blocks segmented in one direction, in pieces named slabs. If these slabs are optically isolated, the scintillation light spreads among a reduced number of photodetectors, increasing the number of optical photons that reach each photodetector, which improves the timing capabilities. In the monolithic direction, the Light Distribution can be characterized and, thus, the Depth of Interaction information can be retrieved, while preserving the sensitivity and good spatial resolution of monolithic detectors. We present here a prototype of a small-animal PET based on 28 semi-monolithic detector modules arranged in two rings of 106 mm inner diameter and covering an axial length of 52 mm.

Speaker: Jose M. Benlloch

Speaker: Carlos Granja (ADVACAM)

Speaker: Vitalii Urbanevych (Master)

Detection of photons in the near-infrared (NIR) range is utilized to implement several quantum imaging and key distribution techniques for remote sensing [1-3]. Our research group is working on a quantum ghost imaging system (QGIS) project that aims to obtain images of distant objects using entangled photons in the NIR region. The photon source exhibiting quantum correlation is composed of a 1554 nm signal photon and an 809 nm idler photon which are generated through spontaneous parametric down-conversion by injecting a 532 nm pump beam into a periodically poled lithium niobite (PPLN) crystal. We have confirmed that the point source is feasible [4] and are now developing a line source to reduce the imaging acquisition time. To detect the 1D idler photons, we are also working on a NIR-sensitive single photon avalanche diode (SPAD) 1D array. In the first stage of the SPAD array development, single SPAD prototypes of different sizes were designed at the Korea Advanced Institute of Science and Technology (KAIST) and fabricated in a 180 nm CMOS technology at the Advanced Micro Foundry (AMF). This study presents the results of the characterization of NIR-sensitive SPADs that operate with a passive quenching mechanism. The key parameters required in QGIS, such as the dark count rate (DCR) and photon detection efficiency (PDE), were evaluated. As a result, the PDE (@ 810 nm) for a SPAD with an area of 60 x 60 um2 ranged from 5% to 25%, and the DCR was at the level of 2 to 75 kHz. Although the results from this prototype are promising, there are still areas that need to be solved to enhance its performance in the future.

Speaker: Gyohyeok Song

Fourth-generation light sources, like free-electron lasers (FELs) and synchrotrons, have greatly advanced X-ray research in many fields. However, high-performance detector technology is needed to fully utilize these facilities. The PulXar system addresses these challenges by offering a range of tunable features for studying detector performance. It provides uniform X-ray illumination and has shown excellent performance in tests. This work presents the design and results of testing various detectors using the PulXar system.

Speaker: David Lomidze (European XFEL)

Single photon detection of fluorescent X-rays down to 452 eV with a signal-to-noise ratio greater than 20 has been demonstrated using 25 um pitch iLGAD sensors, bump-bonded to a charge-integrating readout chip Moench. These iLGAD sensors combined with a thin entrance window developed in collaboration with FBK are optimized for soft X-ray detection by having an excellent quantum efficiency in the corresponding energy range. Additional measurements using monochromatic X-ray photons from 390 eV to 900 eV have been performed recently at the SIM beamline of the Swiss Light Source. The spectral response features double peaks at each photon energy, corresponding to the signals generated by electron- and hole-initiated charge multiplication. It has been found that the ratio of the signals height depends on the design of the gain layer of the iLGAD sensor and the counts under the peaks change with photon energy. To understand this behavior, a customized simulation program has been developed: it takes into account the impact ionization process, carrier drift and diffusion, charge collection by the readout electrodes as well as the electronic and shot noise. The simulation results have been compared to the measurements, which show good agreement to a large extent. The measurement and simulation results will be discussed.

Speaker: Jiaguo Zhang (Paul Scherrer Institut)

Muography is a technique used for scanning by analysis of muon interaction with a target object. Our aim is to develop a portable gas sealed RPC detector prototypes for muography application and to test it for long-term operation to ensure gas stability. For this purpose, various experiments have been conducted such as the I-V curve (which gives information about the working voltage), efficiency with respect to the trigger from plastic scintillators and time response.

Speaker: Mr Vishal Kumar (UCL - CP3)

There are four CANDU-type reactors under IAEA safeguards at the Wolsung site in South Korea; One of them (Wolsung unit 1) was permanently shut down on the 24th of December, 2019. A new spent-fuel verification system(IOVES) in our previous studies was developed to deal with problems of the existing instrument(OFPS), which has been used to re-verify spent-fuels of the CANDU-type reactors. A field test at Wolsung unit 4 in Korea is carried out to evaluate the performance of the newly developed spent-fuel verification system. This paper aims to discuss the results of the field test in terms of sensitivity, ability to distinguish signals from above and below spent-fuel assemblies, effects of radiation scintillation materials, and the validity of using a reference optical fiber to remove background radiations.
Using the existing and new verification systems, as shown in figure 1, we have measured 19 layered spent-fuel bundles in the spent-fuel storage pool of the Wolsung unit 4. The scan speeds of the existing and new ones are 2 mm/sec and 50 mm/sec, respectively. To evaluate the performance of the new instrument according to the scintillator type, the new instrument examined the multi-layered spent-fuels using three different scintillators (p-terphenyl, BC400, and GS30). The signal generated in the optical fiber itself by the interaction of background radiations and the optical fiber has been obtained using a reference optical fiber to which a radiation scintillator is not bonded.
Although the scan speed of the new instrument was more than 20 times faster than that of the existing one, as shown in figure 2, the former’s sensitivity and ability to distinguish the above and below spent-fuel bundles was far superior to the latter. Experimental results also showed that the p-terphenyl organic scintillator performed the best of the three scintillators. Signals that were not visible in results obtained by the Li glass scintillator (GS30) were observed in the signal obtained by the p-terphenyl and BC400 scintillators. The excellent performance of the new verification instrument appears to be mainly due to the high light output and low decay time of the p-terphenyl. It was also confirmed that in the present instrument, the ability to distinguish between the above and below spent-fuel assemblies was improved to some degree by extracting the background radiation signal from the total signal which was produced by both the optical fiber and the scintillation material. On the other hand, for the new instrument, there is little difference in the ability to distinguish the spent-fuel bundle layers. The effects of removing the background radiation would depend on the relative signal amplitude of the scintillation material and the optical fiber. The newly developed verification system is expected to reduce the time and effort required for IAEA safeguards inspection activities and to lower the nuclear operator’s burden.

Speaker: Dr Sung Woo Kwak (Korea Institute of Nuclear Non-proliferation and Control)

In recent years, X-ray imaging detectors in combination with scintillator screens have been widely used in digital x-ray imaging applications. These indirect X-ray imaging detectors are incorporated in the combination of a TFT or CMOS back plane array with different scintillation screens such as typical CsI and GOS materials. Some detectors can be applied with different scintillators in order to optimize the sensitivity and spatial resolution for a dedicated application. The intensity and scattering of visible light generated in the scintillator layer of indirect conversion detector is primarily determined by the X-ray absorption efficiency and light conversion efficiency of the used material.
In this work, we have employed efficient Gd2O2S:Tb(GOS) scintillator film with high atomic number and different thickness for X-ray imaging detectors. A large-area image detector consists of CMOS array with a 204mm x 200mm active area with 2048x2000 pixel array and 100um pixel pitch. A mount of light generated by incident x-ray energy is rapidly scattered before it is sensed on photodiode arrays. Thick GOS screens, which are better at absorbing high-energy x-rays, show strong light blurring and can't be used for high-resolution imaging tasks. In order to solve this severe problem, different deblurring algorithms such as a simple deconvolution using the estimated PSF (point spread function) and special blind deconvolution were applied in indirect X-ray imaging detector and its imaging characterization and the effect in performance was also investigated.
The relative sensivity to X-ray dose, signal to noise ratio (SNR), and spatial resolution in terms of the modulation transfer function (MTF) of different scintillator screens were measured to analyzed the imaging performance. The experiment imaging characerization in accordance with dfferent debluring technique were compared and analyzed. The initial results demonstrated its ability to achieve a high-spatial resolution imaging under low X-ray exposure condition.

Speakers: Dr Bo Kyung Cha (KERI), Mr Hynwoo Lee (Yonsei University)

Current commercially available therapeutic radiation beam energy detection sensors have excellent signal detection efficiency, but have characteristics in which stability is deteriorated due to the occurrence of micro-cracks in the detection sensor according to the change in incident beam energy. In addition, noise generated by the drift of remaining electron-hole pairs for which signal collection has not been performed degrades the reproducibility and precision of the sensor, resulting in a problem in overall signal detection efficiency. In particular, as a major problem in commercial sensors, the energy dependence of the photon beam, directional dependence, thermal effect, and damage to the device due to incident radiation are being discussed as limitations of the silicon diode. This reduces the signal detection efficiency when used for a long period of time, making it impossible to detect signals stably. Therefore, this study aimed to develop a photochromic switching film and a sensor based on a photoconductor-metal oxide composite structure that can exhibit excellent signal detection efficiency in therapeutic radiation QA verification and excellent sensor precision and reproducibility. For measurements, 6 MV and 15 MV energies from LINAC systems (CLINACiX-S, Varian Inc., USA) were used. Electrometers (6517A, Keithley, USA) and oscilloscope (WaveSurfer 510, Teledyne LeCroy, USA) were connected to the manufactured dosimeter to obtain electrical signals from radiation. The sample-to-sample distance is set to 100 cm. The waveform and signal when irradiated with radiation were obtained using an oscilloscope. The obtained signal was calculated from the accumulated amount of charge using ACQ software (Biopac, Acq Knowledge 4.2, Canada).
As a result of plotting the transmission voltage (T-V) curve using a photodiode, the saturation voltage and threshold voltage according to the voltage are estimated to be about 2.54 V for 10% transmittance of the bias voltage and 10.25 V for 90% transmittance bias voltage. It became. Therefore, if the charge carriers generated in the photoconductor-metal-oxide composite set the sensor driving voltage within the dynamic range, the signal detection efficiency can be increased by increasing the linearity of transmission. The reproducibility results according to radiation irradiation. RSD measured values at 6 MV and 15 MV energies were 1.32c% and 1.24%, respectively. As a result of the reproducibility evaluation, evaluation criteria of 1.5% were satisfied at 6 MV and 15 MV energies. This indicates that the signal stability is suitable for use as a radiotherapy QA dosimeter. The linearity results according to dose changes. The R2 values according to linear regression analysis at 6MV and 15MV energies are 0.998. Hence, the evaluation criteria are satisfied, and the output signal is proportional to the dose change. This indicates that it is suitable for use as a radiation therapy QA dosimeter. These results suggest that the film-type perovskite dosimeter is suitable for a radiotherapy QA dosimeter.
[1] D. A. Low, M. M. Jean, F. D. James, D. Lei and O. Mark, Dosimetry tools and techniques for IMRT, Medical Physics 38 (2011) 1313.
[2] Z. Li, Radiation damage effects in Si materials and detectors and rad-hard Si detectors for SLHC,JINST 4 (2009) P03011.

Speakers: YEJI HEO (Department of Nuclear Applied Engineering), Dr Seung Woo Yang (Department of Radiation Oncology, Busan Paik Hospital, Inje University)

In the continuing search for dark matter, new and more complex technologies have been developed with increasing accuracy and background requirements. The Scintillating Bubble Chamber (SBC) detector combines two proven technologies: bubble chambers and liquid argon scintillator experiments. In order to reach the ultimate projected goal, a Seitz threshold of 100eV is required and therefore the scintillation system needs to be well understood.
This system consists of a liquid argon (LAr) scintillator doped with on the order of 100ppm of Xe, with the light collection accomplished using 32 Hamamatsu VUV4 silicon photomultipliers (SiPMs). One of the requirements of the scintillation detection system is the ability to veto single photoelectron (pe) signals. Distinguishing scintillation pe pulses from dark noise and correlated avalanches requires a well understood model of the pe gain, dark noise rate, $\mu$, and the number of correlated avalanches, $N_{CA}$, as a function of temperature and over-voltage. This talk will discuss the efforts of the SiPM characterization chamber consisting of a temperature-variable RF shield inside a vacuum chamber with $10\text{mK}$ temperature stability from 233K to 293K. A preliminary overview on the analysis to extract the pe gain, breakdown voltage, $\mu$ and $N_{CA}$ in a 5us window will also be discussed.

Speaker: Hector Hawley Herrera

Silicon Carbide (SiC) is a wide-bandgap semiconductor that has recently become a topic of intensified interest in the HEP instrumentation community due to the availability of high-quality wafers from the power electronics industry. SiC features multiple advantageous material properties over silicon. It is insensitive to visible light, hypothesized to be more radiation hard, and has much lower leakage currents, even after irradiation. Especially for future high-luminosity experiments, the radiation hardness is an essential parameter. One of the most important metrics associated with radiation hardness is the charge collection efficiency (CCE), which typically decreases with irradiation due to the formation of traps and defects. A thorough understanding of these traps and defects is crucial for estimating the performance of a detector over its lifetime and can open to the door to techniques such as defect engineering.
We present the current status of characterization and simulations for 50 μm thick 4H SiC PiN diodes together with radiation hardness studies. The characterization work includes determination of material parameters of 4H-SiC (ionization energy and Fano factor) and comparisons to TCAD and Monte-Carlo simulations. Recently, significantly increased signals (with respect to unirradiated samples) were reported for neutron-irradiated SiC diodes in forward bias using UV-TPA-TCT, hinting at charge multiplication [1]. We re-investigate neutron irradiated 4H-SiC PiN diodes (fluences between 5·10¹⁴ and 1·10¹⁶ cm⁻² 1 MeV neutron equivalent neq) which have been previously characterized using UV-TCT [2] and alpha spectroscopic measurements [3]. The CCE and transient waveforms were measured in forward and reverse bias using alpha and UV-TCT measurements. Furthermore, I-V and C-V measurements for forward as well as reverse bias voltages of up to 3kV were performed to serve as additional input in understanding observed radiation damage.
For samples irradiated to 5·10¹⁴ and 1·10¹⁵ neq cm⁻², the CCE in the forward direction grows exponentially, surpassing 100% and coinciding with an increase in the leakage current. At the highest irradiation fluence, no exponential behavior was observed. However, the CCE in the forward direction was found to be larger than for reverse bias. For this fluence, the leakage current remained below 1 nA.

Speaker: Andreas Gsponer (Austrian Academy of Sciences (AT))

Speaker: Daria Zhevachevska (Deutsches Krebsforschungszentrum)

In this report we present the results from the two extensive campaigns at the ELI Beamlines, ELI ERIC, on the TI-LGAD prototypes from the TI-LGAD RD50 run production. The focus has been given to the study of the inter-pad region and to the inter-pad distance (IPD) measurements. The TI-LGAD prototypes with the one trench are compared to those with the two tranches. Also, untypical UFSD Type 10 Prototype, with 2p-stops and guard bias ring in between p-stops (produced as a reference prototype in the same batch and from the same wafer as trenched LGADs), is compared to the trenched LGADs with two trenches. The two experimental techniques, the fs-laser based TCT-SPA and the TPA-TCT are compared. In particular, the potential of fs-laser based SPA in resolving the structures of the inter-pad region will be emphasized. We will also discuss the the inter-pad region response to very high intensity injections.

Speaker: Prof. Gordana Lastovicka-Medin (University of Montenegro)

Speaker: Matthew Daniel Buckland (Universita e INFN Trieste (IT))

Effective atomic number (Zeff) is a critical parameter in radiation therapy and nondestructive testing applications. Although dual-energy computed tomography (DECT) is widely utilized for the determination of Zeff, it is associated with several limitations, including increased patient exposure and substantial equipment costs. To overcome these challenges, we propose a novel approach that employs a deep learning model (RegGAN) to achieve accurate Zeff calculation. This method involves the conversion of low-energy CT to high-energy CT, followed by Zeff map generation. In this study, we conducted an in-depth comparative analysis between the RegGAN-based conversion technique and traditional DECT methodologies, evaluating their respective accuracy and noise reduction capabilities. Our experimental results showed that the proposed RegGAN-based conversion method outperformed DECT in terms of Zeff mapping accuracy (approximate 10% improvement). Furthermore, the RegGAN model showed superior performance to alternative deep learning models, such as U-Net, GAN, and Cycle-GAN. Of particular note, the proposed method effectively mitigated noise in high-energy image, leading to enhanced Zeff accuracy. Our findings suggest that the deep learning-based conversion technique presents a promising alternative to DECT, providing a more precise and cost-effective solution for Zeff mapping in radiation therapy and nondestructive testing applications.

Speaker: Minjae Lee (Yonsei University)

Cone-beam computed tomography (CBCT) is an efficient X-ray imaging modality that can reconstruct a wide area with single scan, compared to multi-detector CT. However, in CBCT, more scatters produced through the object reach detector surface, resulting in the reduction of image contrast. Recently, to address this problem, JPI healthcare Co. in Korea developed a prototype two-dimensional antiscatter grid, the so-called crisscrossed antiscatter grid, by adopting micro-controlled sawing process and carbon interspace material to improve its scatter removal ability. However, the most critical obstacle remaining for the successful use of crisscrossed grids in CBCT is the observation of grid artifacts (e.g., ring artifacts on CBCT images), which can result in a misdiagnosis by physicians [1]. In a previous study [2], we developed an effective software-based grid artifact reduction (GAR) algorithm for eliminating the related artifacts in two-dimensional (2D) radiography. In this study, to demonstrate the feasibility of the GAR algorithm to CBCT system with a crisscrossed grid, we modified the GAR algorithm for CBCT and conducted an experiment using a table-top setup. Figure 1 shows the schematic of a crisscrossed grid and an experimental setup used in this study. The setup primarily comprised a conventional X-ray tube (100 kVp and 4 mA), a focused crisscrossed grid (strip density of 43.8 lines/inch), and an a-Si/CsI flat-panel detector (145 μm pixel size).
Figure 2 shows the projection images of MK pro-CT II and ACR phantoms before and after applying the modified GAR algorithm. Figure 3 shows the resulting CBCT images of the phantoms using the standard filtered backprojection algorithm before and after applying the GAR algorithm. Figure 4 shows the measurements of contrast-to-noise ratio (CNR) and HU error of the two phantoms. Here the CNR and HU error of reference images without grid are also shown for comparison. According to our preliminary results, the image quality of the CBCT images were effectively improved by using the crisscrossed grid and the modified GAR algorithm. More quantitative experimental and simulation results will be presented in the paper.

Speaker: Mr DUHEE JEON (Yonsei university)

The recently developed Low-Gain Avalanche Diode (LGAD) technology has gained growing interest within the high-energy physics (HEP) community, thanks to its capability of internal signal amplification that improves the particle detection [1]. Since the next generation of HEP experiments will require tracking detectors able to efficiently operate in environments where expected fluences will exceed 1E17 neq/cm2 [2], it is of the utmost importance the design of radiation-resistant particle detectors. To this purpose, Technology Computer-Aided Design (TCAD) simulations are a relevant part of the current detector R&D, not only to support the sensor design and optimization, but also the radiation damage understanding and modelling. In this contribution, the recent advances in the TCAD modelling of non-irradiated and irradiated LGAD sensors are presented, whose validation relies on the agreement between the simulated and experimental data - in terms of current-voltage (I-V), capacitance-voltage (C-V), and gain-voltage (G-V) characteristics, coming from devices manufactured by different foundries (e.g. HPK, FBK), and accounting for different irradiation levels and temperatures.

Speaker: Tommaso Croci (INFN, Perugia (IT))

In recent years, digital X-ray imaging detectors with indirect detection technology have been widely used in many medical imaging applications such as radiography, fluoroscopy and cone-beam CT. These indirect X-ray imaging detectors are based on the combination of a thin film transistor (TFT) array with several scintillating screens such as typical CsI, GOS materials. Currently, dual-energy (DE) imaging task using a dual-layer X-ray detection type allows the soft and hard structures (e.g. soft and bone tissues) in the object to be selectively visualized,
In this work, we have designed and employed dual-layer based a-Si array backplanes with top layer and bottom layer for X-ray imaging tasks. A prototype large area image detector consists of TFT array with a 43cm x 43cm active area with 3072x3072 pixel array and 140um pixel pitch. Different scintillation combination such as columnar CsI:Tl and Gd2O2S:Tb(GOS) with various thickness and spectral middle filters were used to investigate the imaging characterization. The specific scintillators in dual-layer configuration were selected and implemented for good image quality at low X-ray dose condition.
For imaging characterization of the dual-layer X-ray imaging detector, different scintillating screens were directly coupled on the prototype photodiode array panel. The preliminary important X-ray characterization such as the detector sensitivity to X-ray exposure dose, signal-to-noise-ratio (SNR) and modulation transfer function (MTF) and phantom imaging were measured under practical imaging systems with 60-120kVp tube voltage and adjustable tube current. The experimental results with a dual-layer based flat panel detector using combination of different scintillators and intermediate filter demonstrated its ability to perform accurate dual-energy imaging with single –exposure.

Speakers: Dr Bo Kyung Cha (KERI), Prof. Chang-Woo Seo (Yonsei University), Mr Minjae Lee (Yonsei University)

Due to their unique properties, nanocrystals (NCs) have attracted significant attention in various research fields. The NCs are classified into 0D quantum dots (QDs), 1D nanowires (NWs), and 2D nanoplatelets (NPLs) depending on their structures. Especially, 2D NPLs have the advantage of restricting quantum confinement effects only in the z-axis, unlike other NCs. Furthermore, NPLs composed of core and shell can adjust their properties by changing their structure. In this study, type-II cadmium telluride (CdTe) crowns were combined with cadmium selenide (CdSe) cores to improve the optical and electrical properties. Using 2D CdSe/CdTe core/crown NPLs, an improved indirect X-ray detector with an inorganic/organic hybrid active layer was developed. Figure 1a, shows the hybrid active layer was composed of Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), and CdSe core/CdTe crown NPLs. Figure 1b shows the corresponding energy levels of the proposed detector and the process of charge collection. To perform experiments on the blending ratio, PCDTBT:CdSe core/CdTe crown solutions were prepared in four different ratios of 1:2, 1:1, 2:1, and 3:1. Figure 2a, shows J-V characteristics of the proposed detectors, and Figure 2b, shows the trend of X-ray radiation parameters (CCD − DCD, sensitivity). The detector was optimized when the blending ratio of PCDTBT and NPLs was 2:1, and the highest JSC was 0.190 mA/cm2. Furthermore, radiation parameters showed a similar trend as JSC, and sensitivity was 0.173 mA/Gy∙cm2, which was 77.8% higher than that of the PCDTBT:CdSe core detector [1]. Our results suggest that the use of Type-II CdTe crowns represents a promising approach for enhancing the properties of semiconductor materials and have important applications in a wide range of fields, including electronics, optoelectronics.

Speaker: JAIWON SON (Convergence Semiconductor Research Center, Dankook University, Yongin-Si, 16890, Gyeonggi-Do, Republic of Korea)

Backscatter X-ray imaging techniques are sensitive to organic materials (i.e., low-Z elements) due to a larger Compton scattering cross-section than that of other photon interactions. Therefore, it has the potential to be used as a security screening system to detect organic compounds, such as drugs and explosives. Additionally, it is possible to make a compact device because the X-ray generator and detector are positioned on the same side of the object. Because of these favorable characteristics, backscatter X-ray detection systems have been widely used for detecting illegal items concealed in luggage, screening vehicles, and containers, including detecting landmines in military border areas.
In the present study, a prototype of a backscatter X-ray security scanner for luggage screening was developed, and its performance was evaluated at various tube voltages. This system consists of an X-ray generator, a disk-shaped rotating collimator (i.e., chopper wheel), monolithic large-area detectors with associated signal processing electronics, and a conveyor. By rotating the disk-shaped collimator with slits, a vertically-swept pencil beam is formed, and then the conveyor is moved horizontally to perform an overall scan of the object. To obtain backscatter X-ray images, we utilized phantoms fabricated in accordance with the international standard (ANSI N42.46) as well as actual contrabands provided by the Korea Atomic Energy Research Institute. Using the prototype system, the isolation contrast, which represents the thinnest discernible thickness of an object when the background material differs from the object to be imaged, was determined to be about 1 mm. As shown in Figure 1, the contraband items (i.e., methamphetamine and cannabis) randomly hidden inside the luggage were clearly visible at tube voltages ranging from 80 to 160 kVp. It is expected that the backscatter X-ray security scanner can provide improved detection efficiency for thin objects and/or organic materials.

Speaker: Geunyoung An (Jeonbuk National University)

As a demand for lithium-ion battery (LIB) cells in industry continues to grow, more accurate inspection techniques are required for ensuring quality assurance (QA) during production. Detecting defects accurately, such as metallic foreign matters and crack, is important for inline QA testing, where both fast-processing speed and high accuracy are essential. Particularly, in the post-packaging step, X-rays are usually used for the inspection of LIB cells. Although several detection algorithms have been applied for the inline QA testing, those methods are often difficult to satisfy the requirements of the inline QA testing, mainly because of the computational cost and accuracy. In this study, to overcome this challenge, we proposed an effective method, the so-called parallel-triple detection filtering (PTDF) algorithm. Figure 1 shows the simplified flowchart representing the proposed PTDF algorithm that consists of two processes of the defects detection through the triple filtering consecutively and image fusion. By combining the filtered images with different sensitivity and specificity, the proposed algorithm can improve the detection accuracy of the defects in the LIB cells, saving the processing time. To demonstrate the feasibility of the proposed method, we performed an experiment using a table-top setup that consisted of an X-ray tube (70 kV_P and 1.4 mAs) and a CMOS flat-panel detector (49.5 μm pixel resolution). Figure 2 shows the experimental setup, battery cell used in the experiment and its radiograph, and the defects detection maps obtained using the Ostu, adaptive thresholding, k-means, and proposed methods. According to our preliminary results, the proposed algorithm effectively detected the abnormal structures in LIB cells and outperformed the existing algorithms in terms of accuracy and time. More quantitative experimental results will be presented in the paper.

Speaker: Mr Woosung Kim (Yonsei university)

Radiography is one of the most commonly used diagnostic tools in veterinary practice and, particularly, denoising is one of the important image processing tasks. Robust noise removal will improve the image quality of diagnosis. There are many state-of-the-art noise reduction methods that have been studied in the image processing literature. Nevertheless, no algorithm that can robustly remove image noise has been universally accepted because the resulting image performance of a denoising algorithm can vary substantially, depending on the imaged subject, X-ray imaging system, and operating conditions. In this study, to overcome this challenge, we proposed an effective denoising method based on a modified image pyramid incorporated with guided filtering for the practice of companion animals. Compared to traditional pyramid-based approaches that use a Gaussian filter and two-stage pyramid, our approach uses a guided filter and three-stage pyramid to robustly separate noise component from the image, keeping image details . Figure 1 shows the schematics of the traditional and proposed pyramids. To demonstrate the feasibility of the proposed denoising algorithm, we performed the noise reduction of a dog’s radiograph, which was taken at an animal hospital, using the proposed algorithm, and evaluated the image quality in terms of the structural similarity and peak signal-to-noise ratio. Figure 2 shows the resulting images of a dog using several denoising algorithms: noisy image and denoised images using wavelet, traditional pyramid, proposed pyramid with Gaussian filtering, and proposed pyramid with guided filtering, followed by BayesShrink-based hard thresholding, respectively. According to our preliminary results, the proposed algorithm achieved the highest image performance among the other denoising algorithms, indicating its efficacy for reducing noise in animal radiography. More quantitative evaluation of the image performance will be presented in the paper.

Speaker: Mr Woosung Kim (Yonsei university)

The irradiation study of silicon diodes was carried out in order to evaluate the effects of gamma-irradiation on p-type silicon. Three types of n-in-p diodes from different manufacturers were studied. The diodes had comparable active area and thickness but different initial resistivities and oxygen concentration. Thanks to that we were able to determine how different initial parameters influence radiation-induced changes in measured electrical characteristics. The diodes were irradiated by a Cobalt-60 gamma source to total ionizing doses ranging from 0.50 up to 8.28 MGy, and annealed for 80 minutes at 60°C. The main goal of the study was to characterize the evolution of the full depletion voltage with total ionizing dose, by measuring capacitance-voltage characteristics, and the gamma-radiation induced displacement damage by measuring current-voltage characteristics.

Speaker: Iveta Zatocilova (Albert Ludwigs Universitaet Freiburg (DE))

Energy Dispersive X-ray Spectroscopy (EDS) is a common technique in electron microscopy to identify the chemical composition of samples. The standard method for analyzing the measurement data is semi-empirical, where the necessary correction factors have been determined decades ago using detectors much less sensitive than current ones.
This work shows that the Geant4[1] and AllPix2[2] open-source simulation tools can be used to accurately model the full EDS system. This is a first step towards a complete first-principles determination of the elemental composition from measured data, precluding the need for independently determined correction factors.
The simulations are compared to Scanning Electron Microscopy (SEM) measurements for validation and differences between simulation and measurements are highlighted.

Speaker: Thijs Withaar (Sioux Technologies)

Speaker: Dr G. Lioliou (University College London)

For the decommissioning of f*ckushima Daiichi Nuclear Plants, a real-time dose-rate monitor under the high dose-rate situation is required to remove the debris remaining inside the plants. We have proposed a dose-rate monitor consisting of a scintillator, optical fiber, and CCD spectrometer. Since an over 100-m long optical fiber is used, some noises (“fiber noise”) such as scintillation photons generating from the fiber itself and Cherenkov photons with a dominant emission band of below 550 nm must be separated from the signal from the scintillator. Therefore, longer emission wavelength (over 650 nm) and high light output are required for the scintillator.
　We focused on a Cr-doped Gd3Ga5O12 (Cr:GGG) scintillator as such applications. In addition, we focused on noise region in emission spectra that has some information originating from fiber noise. This noise is expected to show the dose rate information through the fiber. Thus, we report the radiation dose-rate monitoring system and the analysis of the noise data that we describe as “one-dimensional dose-rate distribution”.
Cr:GGG single crystal was grown with micro-pulling method and its optical properties were evaluated.
　One-dimensional dose-rate distribution was also evaluated with the fiber noise. Using this noise information, we can evaluate the integrated dose through the fiber. Moreover, emission spectra of the fiber noise are expected to be changed due to the absorption in the fiber, and the shapes of the spectra are expected to have position information for source of fiber noise. To evaluate the one-dimensional dose-rate distribution, demonstration of the monitoring system coupled with 20 m-long optical fiber and CCD spectrometer was operated. Optical fiber was placed around the 60Co source (approximately 60 TBq), and emission spectra of the fiber was acquired at each irradiated fiber length under high dose rate conditions (approx. 10-700 Gy/h).
　We grew Cr:GGG single crystal with Its emission wavelength was approx. 730 nm. As results of the demonstration, the noise intensities were well fitted with power function as a function of the product of fiber length and dose rate (integrated dose), and the fiber noise information can be used as dose rate information as one-dimensional imaging. In this paper, we discussed the evaluation of the relation of the intensity ratio of Cr:GGG and optical fiber noise and irradiated length of the fiber.

Speaker: Daisuke Matsukura (Tohoku University)

Photon counting computed tomography (PC-CT) is a new type of CT that is being studied worldwide. The radiation dose produced by PC-CT can be reduced up to 1/100 of that produced by the currently available CT scanners. In addition, obtaining information from multiple energy bands makes it easier to acquire images without artifacts and leads to accurate material decomposition. In this study, we use a detector system composed of a 64-channel multi-pixel photon counter (MPPC) coupled with a scintillator, which renders the proposed system to be simple and cost effective. We used the PC-CT in three experiments performed on mice and rats. The first experiment involves the in-vivo imaging of iodine-injected mice. The results showed that iodine accumulated in the kidneys and the bladder. Furthermore, we also captured time-shift images of the mice and successfully observed iodine being faded out of the kidneys. The second experiment involves the imaging of gold nanoparticle (AuNP)-injected mice. In this experiment, mice were sacrificed before imaging. AuNPs were successfully imaged in the kidneys. In addition, we performed high-resolution imaging and 3D reconstruction. The final experiment involved ex-vivo imaging of rat livers injected with a Gd-based contrast agent. Liver imaging revealed a difference in contrast between the non-injected liver and the Gd -injected liver. In addition, we estimated the concentration of the contrast agent, and the results indicated that the liver could not absorb more than 2.5 mg/mL of Gd-based contrast agent. We conclude that these findings have the potential to advance the clinical application of PC-CT. In the future, we aim to visualize the mechanism of drug delivery system in the human body and expand the detector area.

Speaker: Mayu Sagisaka

Dental panoramic imaging is a standard X-ray technique in dentistry that produces a single image of the facial structures, including both maxillary and mandibular arches and their supporting structures. A typical panoramic system consists of a slit-collimated X-ray tube, a linear-array type detector, and predetermined sequences for the panoramic scan motion and signal readout from the detector to focus a specific dental arch. Panoramic image is commonly reconstructed using the shift-and-add (SAA) algorithm [1], where it is gradually built up by adding panoramic projections in a way that stacks the focusing sections of the panoramic projections consecutively. In this study, we propose a new panoramic reconstruction method, the so-called angle-limited backprojection (ALBP) algorithm, for low-dose panoramic imaging [2]. Figure 1 shows the schematics of panoramic reconstruction methods of the SAA and proposed ALBP algorithms. In the ALBP algorithm, rays to be backprojected onto a given spherical voxel, which is established along the dental arch, are selected from the measured panoramic projection data and then backprojected, as in computed tomography reconstruction. To validate the efficacy of the proposed algorithm, we conducted a series of simulations and successfully reconstructed panoramic images using both the SAA and ALBP algorithms. Figure 2 shows the simplified data processing for the proposed ALBP algorithm and the 3D numerical dental arch phantom used in the simulation. Figure 3 shows the resulting panoramic images of the phantom reconstructed using the SAA and ALBP algorithms: (a) with all and (b) with half projection data. The preliminary simulation results showed that the image quality of the panoramic image obtained using the ALBP was better than that of the image obtained using the SAA. In addition, the panoramic image reconstructed using the ALBP with half projection data gave much better image quality than that using the SAA with the same projection data, indicating the potential of low-dose panoramic imaging. More quantitative simulation and experimental results will be presented in the paper.

Speaker: Hyesun Yang

A micro-pattern gaseous detector with pixel readout is being developed for the beam monitoring for the CSR external-target experiment (CEE) at HIRFL. Demanded by the physics program of the CEE experiment, it not only monitors the lateral beam density distribution, but also measures the lateral position of each beam particle with a spatial resolution better than 50 $\mu$m and with a rate up to $10^6$ pps. The beam monitor mainly consists of two field cages inside a gas vessel with electrical fields orthogonal to each other, and four custom-designed charge sensing and readout chips on the anode of each field cage. The gas electron multiplier (GEM) is adopted for some beams with less ionizing power. The simulation of the drift electric field, gas properties, signal induction and spatial resolution of the detector has been carried out to optimize the geometrical set-up, to evaluate the expected performance, and to calculate the requirements on the chip characteristics. In particular, as the beam intensity increases, the ion back flow (IBF) from electron avalanches inside the GEM and the ions produced by the beam particles leads to sizable electric field distortion in the drift region, which worsens the spatial resolution of the detector. In this poster, the design and simulation studies of the beam monitor, especially the modelling and the correction of the space charge effect, are presented

Speaker: Zhen Wang

This study proposes a new signal multiplexing method for molecular imaging systems used in nuclear medicine, which can reduce the number of readout channels by utilizing charge reset amplifiers and a deep learning model. The results show that the proposed method can reduce 16 readout channels to one without distorting the original signal, using charge reset preamplifier and deep learning architecture. The proposed method is tested using a 4x4 Ce:GAGG scintillator array and a 4x4 SiPM array with a 137Cs radiation source. The average energy resolution was 11.87%, and the crystal positioning map also indicates that distinct SiPM array pixel identification is possible without the need for a charge division method. The proposed method could help reduce the cost and complexity of NM systems while maintaining or improving their performance. Future work will focus on expanding the technique to accurately identify a greater number of crystals while also increasing the ratio of crystals to SiPMs.

Speaker: Semin ‍Kim (Department of Bioengineering, Korea University, Seoul, South Korea)

Photon-counting computed tomography (PC-CT) is a type of next-generation X-ray CT system for medical applications. It enables quantitative evaluation, such as concentration estimation, which is not possible with conventional CT systems. This is because the number and energy information of the individual incident X-rays can be obtained by reading them out in pulse form. By utilizing this property to estimate the concentration of contrast agents injected into the body, it is expected to expand the possibilities of novel diagnostics, such as drug delivery systems. Therefore, we established the SiPM-based PC-CT system combined with the YGAG scintillators [1, 2, 3] and evaluated its performance in several cases [4, 5]. However, to estimate the concentration of contrast agents flowing inside small animals more accurately, the temporal resolution of CT imaging needs to be improved [5]. In such a situation, the sparse-view CT technique, which involves reconstructing CT images from the smaller number of projections than that of conventional way [6], is an attractive method that enables CT imaging with shorter duration without degrading image quality. In this presentation, we report the initial results of an image quality evaluation of sparse-view CT images obtained with our established SiPM-based PC-CT system. We used static phantoms equivalent to an iodine contrast agent as the subject (Fig. 1). The six energy thresholds were set to 11, 33, 55, 65, 75, and 90 keV; and the tube voltage and tube current were set to 120 kV and 0.1 mA, respectively. We then obtained the projection data and applied the image reconstruction method based on total variation minimization to the sparsely view-sample sinogram data with the number of projections reduced to 1/5 of the original (Fig. 2). As part of the results, from the sparsely sampled data, we successfully reconstructed the CT images equivalent to ones from the sinogram data of the original. Furthermore, we obtained the correct CT values in the region of 5 mg/mL of iodine within the standard deviation. In addition, the standard deviation with sparse-view CT is 34.0% smaller than the conventional one in the 11–33 keV energy band (Fig. 3). This means that the total imaging time could be reduced to 1/5 while improving image quality by 34.0%, i.e.; the X-ray dose could also be reduced to 1/5. Finally, we also performed sparse-view CT imaging on mice injected intravenously with iodine contrast agents. We briefly report the results of the quantitative evaluation.

Speaker: Daichi Sato (Kanazawa University)

Two-dimensional (2D) X-ray inspection systems have been widely used for homeland and aviation security, but they still have limitations in recognizing 3D shape of the hidden threats. Hence, there has been increasing demand for computed tomography (CT) scanner for carry-on baggage screening. In a previous study [1], we designed a new stationary CT baggage scanner with compressed-sensing (CS) algorithm and -angle spacity, comprising several dozen pairs of X-ray source and linear array-type detector placed within a scan angle of 180 degrees at an equiangular distance. Our previous results showed that the proposed CT configuration significantly reduced the streak artifacts appearing in the standard filtered-backprojection (FBP) reconstruction, thereby considerably improving the image quality. In this study, as a continuation of our X-ray imaging R&D, we replaced the linear array-type detector in a previous design with a dual-layer detector (X-Card 1.5-64DE, Detection Technology Co.) and applied a typical material decomposition algorithm to separate soft and dense materials for enhancing the detection of threats. Dual-energy CT is a theoretically well-established X-ray technique used to differentiate and classify material composition in CT using projection images acquired at two different X-ray energy spectra [2]. In addition to material-specific images, the dual-energy projection data can be used to synthesize virtual monochromatic CT images as the potential to reduce beam-hardening artifacts that are usually observed in traditional polychromatic CT images. Before the practical implementation of the proposed dual-energy CT baggage scanner, we conducted a series of simulations to validate its efficacy. Figure 1 shows (a) the schematic of a stationary dual-energy CT scanner with pi-angle sparsity and a dual-energy detector and (b) X-ray energy spectra used in the simulation for material decomposition. Figure 2 shows the schematic of the proposed dual-energy CT algorithm to separate soft and dense materials. Figure 3 shows the preliminary simulation results of a stationary dual-energy CT scanner with pi-angle sparsity and material decomposition. More systematic and quantitative simulation and experimental results will be presented in the paper.

Speaker: Jiyong Shim (Yonsei university)

Positron probes are widely used to accurately localize malignant tumors by directly detecting positrons emitted by positron-emitting radiopharmaceuticals that accumulate in malignant tumors. However, the conventional method of direct positron detection cannot distinguish some γ-rays, resulting in misidentification of γ-rays as positrons and increasing the error rate of positron detection. In this study, an Autoencoder-based positron detection algorithm is proposed to improve the accuracy of positron detection by analyzing the energy distribution in each scintillator of the multilayer scintillator detector for discriminating between true and false positrons. The Autoencoder was trained to separate the combined signals generated by the multilayer scintillator detector into two signals from each scintillator. An energy window was then applied to the energy distribution obtained using the trained Autoencoder to distinguish true positrons from false positrons. The proposed method was evaluated and compared with the conventional method in terms of performance, sensitivity and error rate for positron detection. The results showed that the proposed method can increase the sensitivity of positron detection while maintaining a low error rate compared to the conventional method. Specifically, the proposed method had a higher sensitivity than the conventional method when both methods had the same error rate. In addition, the proposed method had a lower error rate than the conventional method when both methods had the same sensitivity.

Speaker: Dr Chanho ‍Kim (Korea Atomic Energy Research Institute (KAERI), Daejeon, South Koreauth Korea)

Recently, a metal-oxide thin-film transistor (TFT)-based flat-panel x-ray detector has been paid attention to its fast readout time and low-noise characteristic. We analyze empirically the signal and noise characteristics of an indium gallium zinc oxide (IGZO) TFT-based detector in comparison with those of the conventional hydrogenated amorphous silicon (a-Si:H) TFT-based detectors. We compare the large-area transfer functions of the detectors as a function of air kerma at their entrance surface. We perform the mean-variance analysis to address the systems’ gain and electronic noise. The signal and noise performances are evaluated by measuring the modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). The low-dose imaging capability of detectors is assessed by investigating the large-area or zero-frequency DQE, including a DQE reduction factor which is introduced in this study, as a function of air kerma. Throughout this study, we evaluate the value of the IGZO detector in terms of dose efficiency, in particular, compared to the conventional a-Si:H detectors.

Speaker: Seokwon Oh (School of Mechanical Engineering, Pusan National University)

For the application to megavoltage (MV) or mega-electron volt (MeV) imaging, we investigate theoretically and empirically the signal and noise characteristics of thin gadolinium oxysulfide phosphor detectors. For several phosphor detector designs, we perform the Monte Carlo (MC) simulations for various MV x-ray spectra from linear accelerators and gamma-rays (ranging from hundreds of keV to a few MeV) from radioisotopes. Applying the moment analysis to the MC pulse-height measurements, we estimate the energy-absorption signal, its induced noise, and the detective quantum efficiency (DQE). In the analysis, we also take into account the effect of electron-buildup metal layers for possible signal enhancement, which are placed on the top of phosphor detectors, and investigate the role of secondary radiations on the DQE. We construct phosphor-coupled CMOS detectors and report their detection performance for image quality indicators under MV and MeV irradiation environments. This study will be helpful for the development of bendable detectors.

Speakers: Ho Kyung Kim (School of Mechanical Engineering, Pusan National University), Seungjun Yoo (School of Mechanical Engineering, Pusan National University)

A sandwich-like, double-layered detector can perform dual-energy imaging (DEI) at a single shot of x-ray exposure without object-motion artifacts. The energy separation between the measurements from two (front and rear) detector layers can be further adjusted by inserting an x-ray beam-attenuating material between them. However, the design of the interdetector filter highly impacts the dose efficiency by changing the number of x-ray photons reaching the rear detector layer in the sandwich detector. We develop a cascaded-systems model to assess the signal and noise propagation in the sandwich DE detector and estimate the DE detective quantum efficiency (DQE) in terms of filter designs. We validate the developed DE-DQE model by comparing it to the measurements. The developed model will be helpful for better design and operation of sandwich detectors.

Speaker: Hubeom Shin (School of Mechanical Engineering, Pusan National University)

Speaker: Mr Florian Beißer (Erlangen Centre for Astroparticle Physics)

Speaker: Prof. Peter Dendooven (Helsinki Institute of Physics, University of Helsinki)

Transmission X-ray security scanners are used to detect the smuggling of contraband articles, including weapons, narcotics, and explosives for homeland security. Current X-ray scanners use fixed tube voltages (i.e., 160 kVp); hence, it has a limitation in detecting thinly coated and/or low-density objects. To overcome this limitation, we are designing an X-ray scanner applying a variable tube voltage depending on the physical/chemical properties of the object being inspected. To this end, the Monte Carlo simulations with Geant4 and MCNP6 were performed to optimize the design of the X-ray scanner with variable tube voltages.
In the present study, we experimentally validated the reliability of the Monte Carlo simulation model for the X-ray scanner. The X-ray images obtained by the experiment were compared with the simulated images. The experimental setup is shown in Figure 1. The source-to-object distance (SOD) and the source-to-detector distance (SDD) was 70 cm and 120 cm, respectively, as applied to a typical security scanner. The tube voltage and the current were 80 kVp and 10 mA, respectively. The object was scanned at a speed of 0.2 m/s on a conveyor system to obtain the images. Simulated images were obtained using the X-ray source term produced from a monoenergetic electron beam bombarded onto the target (i.e., 80 kVp). 4-D simulations were performed for a moving object. The profiles of the simulated and experimental images were compared to validate the simulation model. It was found that the difference in pixel count between experiment and simulation was less than 5%. Thus, we concluded that our simulation model for the X-ray scanner can be considered reliable.

Speaker: Junsung Park (Jeonbuk National University)

Speaker: Ondrej Zapadlik

The pile-up phenomenon can cause distortion in the recorded data and make it difficult to accurately measure the properties of individual radiation events. This issue can lead to an underestimation of the quantitative analysis, especially in radioisotope identification through gamma-ray spectroscopy. Recently, deep learning-based studies for pile-up correction have been conducted. Those studies established datasets including bi-exponential shapes through experimental or mathematical modeling and proposed deep neural networks that were robust to noise, which resolved spectrum distortion. In this study, we perform a comparative study using three kinds of deep neural networks to select the best model for restoring piled-up pulses. We will optimize deep neural networks and choose the best pile-up correction model based on the restoration results of the spectrum distortion. We expect that this study serves as useful data to select and utilize the best deep neural network for the correction of pile-up caused in high radiation environments.

Speaker: Mr Wonku Kim (Korea Advanced Institute of Science and Technology)