Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Thallium Bromide (TlBr) semiconductors have been extensively studied for their potential as room-temperature gamma-ray detectors, owing to their advantageous material properties. Recent advancements have demonstrated that timing performance in TlBr detectors can be enhanced by incorporating Cherenkov photon detection during gamma-ray interactions. In this study, TlBr detector (5 × 5 × 5 mm³) was investigated through a combined analysis of electrical charge and Cherenkov light signals. The depth of interaction (DoI) correction applied to the trapezoidal filter output yielded significant improvements in energy resolution, reducing it from 5.6% to as low as 2.51% FWHM at 511 keV and from 4.6% to as low as 1.94% FWHM at 662 keV, within specific C/A ratio ranges. The drift time, ranging from 2 to 30 μs, was found to be proportional to the C/A ratio, covering 4 to 9 photoelectrons. Furthermore, a time resolution of 511 ps was achieved at 6 photoelectrons, based on the FWHM of the time difference distribution in coincidence measurements at 511 keV using a ²²Na source. These results highlight the potential of TlBr detectors for achieving high energy and timing resolution in gamma detection, particularly for Compton-PET systems.

DOI： 10.1088/1748-0221/19/11/c11017

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/19/11/C11017/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3018688

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2024.169426

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Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press Ltd.  

A prototype system based on a combination of 4π sensitive gamma imaging and simultaneous localization and mapping (SLAM) was developed to find unknown radiation source(s) rapidly. The system consisted of a spherical visible camera, a three-dimensional light detection and ranging, a CdTe pixel array detector for 4π gamma imaging, a portable battery, and a control laptop personal computer; these were mounted on an unmanned vehicle. In a search area of 16 × 16 m² with a height of 3 m, the prototype system successfully demonstrated the finding of a ¹³⁷Cs point source with an activity of 0.67 MBq in the surrounding thin walls.

DOI： 10.20965/jrm.2024.p0079

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The conventional nuclear medical imaging, such as PET and SPECT, visualizes the accumulation of radioisotopes in the human body and has been widely used for diagnosis of cancer and other diseases. Perturbed angular correlation is a powerful sensing tool detecting local electro-magnetic environment and has been used for chemical analysis or nuclear physics research. The use of perturbed angular correlation in nuclear medicine is recently proposed and pH sensing capability with liquid $$^{111}$$In has been confirmed. In more practical applications, DOTA based radioisotope labeled drug delivery is common in nuclear medicine. This study aims to characterize the pH dependance of perturbed angular correlation in Psyche-DOTA chelated $$^{111}$$In with the custom ring-shape gamma-ray detectors. The observed transition in anisotropy of cascade gamma-ray emission can contribute to the detection of a specific phenomenon changing pH inside the human body.

DOI： 10.1007/s10751-024-01864-7

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Other Link： https://link.springer.com/article/10.1007/s10751-024-01864-7/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

T2 relaxation time in magnetic resonance imaging (MRI), which is determined by magnetic dipole interactions, has been employed as a parameter for tumor detection. However, owing to the lack of MRI detection sensitivity, nuclear medicine imaging is currently the basic option for tracking low concentrations of chemical probes. Previous studies utilizing cascade radionuclides have focused on the relaxation due to electric quadrupole interactions. However, magnetic dipole interactions, which are crucial in MRI, remains to be elucidated. In this study, we determined the magnetic relaxation rate by using 111In, a cascade radionuclide used in clinical single-photon emission computed tomography (SPECT) scans. As the angle between the gamma rays from the nuclei is affected by the electrical and magnetic interactions acting on the nuclei, we measured the angular correlation ratio by using eight gadolinium gallium garnet (GAGG) multi-pixel photon counter (MPPC) 8 × 8 array detectors and extracted the magnetic relaxation rate. Consequently, we obtained a rate that increased with the Fe concentration, similar to the T2 relaxation rate, although it was influenced by the inhomogeneity of the external magnetic field. This study utilized low concentrations of the liquid-state radionuclide, which is commonly used in clinical nuclear medicine imaging scans and is expected to provide much higher sensitivity and more selective detection of tumors than conventional MRI.

DOI： 10.1063/9.0000665

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Language：English   Publishing type：Research paper (international conference proceedings)  

Web of Science

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

ToT-ASIC2 is a new custom front-end application specific integrated circuit (ASIC) to readout silicon photomultiplier (SiPM) and multi-pixel photon counter (MPPC) for time-of-flight positron emission tomography (ToF-PET). ToT-ASIC2 is a 64-channel ASIC fabricated using a commercial 0.25 μm CMOS process. Each channel has an input-current buffer that sends signals to the SLOW and FAST paths, which are used for incident radiation energy and timing information, respectively. Time-over-Threshold (ToT) signals from these paths are combined into one ToT signal to be output outside the ASIC. The power consumption is approximately 2.9 mW per channel.

This study developed a detection system comprising an MPPC with coupled GAGG pixelated scintillators, a front-end board with ToT-ASIC2 and ToT-DAQ. Consequently, energy and timing measurement experiments were performed using this system to confirm the ToT-ASIC2 energy- and timing-resolving capability. Prototype positron emission tomography experiments with ²²Na indicated an energy resolution of 6.7% for 511 keV with the coincidence timing resolution being 215 ps.

DOI： 10.1088/1748-0221/18/09/p09033

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/18/09/P09033/pdf

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2023.168305

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Publishing type：Research paper (scientific journal)   Publisher：Stichting SciPost  

The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of ^{57}Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.

DOI： 10.21468/scipostphysproc.12.041

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

The reduction of background events, such as random and scatter events, can improve positron emission tomography (PET) images quantitatively. The quantum entanglement property of annihilation photons has been theoretically studied and experimentally validated. Recently, simulation studies on PET image reconstruction using the quantum entanglement property of annihilation photons and studies on the measurement of entanglement and polarization properties with scintillation crystal arrays demonstrated that PET images with less background can be achieved. This study utilized the quantum entanglement property of annihilation photons in a typical PET system with block detectors. A data acquisition method for quantum entanglement PET (QEPET) and system response modelling for QEPET image reconstruction were proposed and implemented. An experimental study was conducted using a small animal PET system composed of Ce:GAGG scintillation crystals whose dimensions are 2.5 × 2.5 × 4mm³. The diameter of the system was 79.3 mm. Signals from all individual crystals were processed parallelly and independently; thus, Compton scatter and absorption crystals within a module were obtained directly. The 28 MBq experiment result revealed the random background ratio of QEPET was approximately 20% lower than that of PET and the count rate of QEPET was approximately 0.1% that of PET. Evaluation on reconstructed images from the 28 MBq experiment revealed that the signal-to-background ratio of QEPET was approximately two times better than that of PET while the signal-to-noise ratio of QEPET was about 77% of that of PET. The method proposed in this study is expected to improve PET images with high background, such as those with a high activity and high background gamma rays and improve range verification in proton therapy.

DOI： 10.1088/1748-0221/18/07/p07007

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/18/07/P07007/pdf

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

A Compton camera is a gamma ray imaging system that produces images by superposing Compton cones calculated from Compton kinematics. However, the reconstructed images exhibit a high background. In this study, the angular correlation and polarization correlation were used to decrease the background. ¹¹¹In, which emits 171 keV and 245 keV cascade gamma rays, was imaged using Compton camera modules in the ring structure. The 3D list-mode ordered subset expectation maximization method was used to reconstruct the images. Probability modeling of events reflecting angular and polarization correlations was applied to the image-reconstruction algorithm. The results were compared with those of a typical Compton camera method using only 245 keV Compton cones. The sensitivity of the proposed method was 1.03% of that of the typical method. However, compared to the typical method, the application of angular and polarization correlations improved the signal-to-background ratio. The proposed method is expected to be useful in capturing low-background images wherein a ring-type Compton camera and cascade photon-emitting nuclides can be used.

DOI： 10.1088/1748-0221/18/05/c05012

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/18/05/C05012/pdf

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2023.168122

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Our group has been developing DPECT (Double Photon Emission CT) to enhance nuclear medicine diagnostics using cascade nuclides that emit multiple gamma rays simultaneously. It is possible to detect the local environment around the nuclide by examining the angular correlation of the emitted cascade gamma-rays. In this study, with the goal of developing a new imaging method combining ultrasound and nuclear medicine, we investigated the effect of ultrasound on cascade gamma-ray emission and found that the angular correlation could be changed by a micro-electric field around ¹¹¹In in an aqueous solution caused by ultrasound irradiation. Using 8 × 8 array of GAGG scintillators as a detector and Hamamatsu Photonics 8 × 8 MPPCs as a photomultiplier, eight detectors were used and arranged in a ring shape to surround the point source ¹¹¹In from 360° direction. For the readout system, using a dynamic ToT board, read out its channel information, energy information as ToT signal, and detection time information simultaneously and independently concerning gamma-ray detection. We measured the angular correlation change with four types of ultrasound intensities of 0.05 V, 0.10 V, 0.15 V, and 0.20 V input voltage, and found that the gamma-ray emission angle distribution decreased by about up to 5% around the 90° direction and increased by about up to 5% around 0° and 180° for an ultrasound with an input voltage of 0.15 V or higher.

DOI： 10.1088/1748-0221/18/04/c04001

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/18/04/C04001/pdf

Publishing type：Research paper (scientific journal)   Publisher：Walter de Gruyter GmbH  

Abstract

Multi-molecule imaging and inter-molecular imaging are not fully implemented yet, however, can become an alternative in nuclear medicine. In this review article, we present arguments demonstrating that the advent of the Compton positron emission tomography (Compton-PET) system and the invention of the quantum chemical sensing method with double photon emission imaging (DPEI) provide realistic perspectives for visualizing inter-molecular and multi-molecule in nuclear medicine with MeV photon. In particular, the pH change of InCl3 solutions can be detected and visualized in a three-dimensional image by combining the hyperfine electric quadrupole interaction sensing and DPEI. Moreover, chemical states, such as chelating, can be detected through angular correlation sensing. We argue that multi-molecule and chemical sensing could be a realistic stream of research in future nuclear medicine.

DOI： 10.2478/bioal-2022-0081

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Walter de Gruyter GmbH  

Abstract

Cascade nuclides emit two or more gamma rays successively through an intermediate state. The coincidence detection of cascade gamma rays provides several advantages in gamma-ray imaging. In this review article, three applications of the double photon coincidence method are reviewed. Double-photon emission imaging with mechanical collimators and Compton double-photon emission imaging can identify radioactive source positions with their angular-resolving detectors, and reduce the crosstalk between nuclides. In addition, a novel method of coincidence Compton imaging is proposed by taking coincidence detection between a Compton event and a photopeak events. Although this type of coincidence Compton imaging cannot specify the location, it can be useful in multi-nuclide Compton imaging.

DOI： 10.2478/bioal-2022-0080

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are both established imaging technologies in nuclear medicine that are clinically available. However, simultaneous PET and SPECT nuclide imaging is difficult to accomplish with current equipment because of their distinct principles. In light of this, we have developed and demonstrated a GAGG scintillator based Compton-PET hybrid imaging system capable of performing PET and Compton imaging simultaneously. Alternatively, the CeBr₃ scintillator possesses more desirable properties, including a high light yield (>60000 photons/MeV), a fast decay time (∼19 ns), and an excellent energy resolution (<4%@662 keV). Herein, we developed an 8 × 8 array of CeBr₃ detector based instrumentation by using 64 channel fast signal processing slew rate limited Time over Threshold (ToT) based application-specific integrated circuits and a field programmable gate array ToT data acquisition system with a 62.5 ps accuracy. Furthermore, we evaluated the system’s basic performances. The mean and greatest energy resolutions were 10.1% and 6.0% (FWHM) for 662 keV. The time resolution was 239 ps (FWHM) after offset calibration. We also achieved a proof-of-concept based on single source.

DOI： 10.1088/1748-0221/17/10/c10002

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/17/10/C10002/pdf

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

In the clinical situation of positron emission tomography (PET) scans, an activity of an approximately few hundred megabecquerels (3.7 MBq/kg) is used for injection. Monitoring and imaging of moving radioisotopes is useful in clinical applications, such as tracer injection and leakage monitoring in PET scan protocols. We have developed a Compton imaging and PET coincidence system to monitor a moving radioisotope using 8 × 8 GAGG crystal arrays coupled to SiPM arrays with dynamic time-over-threshold-based individual readout circuits, and its imaging performance is considered. The measured resolution of PET and Compton imaging is 3.2 mm and approximately 17 degrees for a ²²Na point source. In the experiment, radiotracers with activities from 11.2 MBq to 93.3 MBq moving with speeds from 1 mm/s to 10 mm/s were used for mimicking the blood flow. Both reconstructed images of PET and Compton imaging successfully visualized the movement, except for Compton imaging in the 93.3 MBq case. PET shows better activity-tracking capability and radio-tracer speeds up to 100 MBq. In contrast, Compton imaging has a wider field of view (FOV) to monitor a larger area than the limited FOV in a PET system. We believe that this work can contribute to solutions of various medical problems such as blood flow measurement and extravasation detection.

DOI： 10.1088/1748-0221/17/07/c07018

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/17/07/C07018/pdf

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Compton imaging based on Compton scattering kinematics has the potential to visualize multi-nuclides by discriminating the total energy of Compton scattering and photoelectric absorption events. This feature enables us to perform multi-tracer imaging that reflects different functional information in nuclear medicine, resulting in a definitive diagnosis and being useful for biological and medical research. One of the challenges with multi-nuclide imaging is the crosstalk artifacts caused by scattered photons of higher energy gamma-rays. In this study, we investigated the potential benefits of the double photon coincidence detection as a drastic crosstalk reduction method. Coincidence detection of successive gamma-rays can differentiate nuclides and reduce the background caused by other nuclides' gamma-rays because some nuclides emit two or more gamma-rays in rapid succession. In this study, we focused on the coincidence detection of a Compton event and a photoelectric absorption event, and we showed simultaneous double photon emitter imaging of ¹¹¹In and ¹⁷⁷Lu with a ring-type Compton imaging system. The artifacts caused by other nuclides' gamma-rays were reduced by extracting Compton events coincident with photoelectric absorption events. The coincidence Compton images demonstrated a signal-to-background ratio improvement of 1.1–1.7 times over the one of no-coincidence Compton images, despite a drop in intrinsic detection efficiency of the order of 10^-2. This strategy of directly reducing crosstalk will be useful in other combinations imaging such as of ¹¹¹In (or ¹⁷⁷Lu) and a positron emission tomography nuclide.

DOI： 10.1088/1748-0221/17/04/p04001

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/17/04/P04001/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/sii52469.2022.9708756

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Publishing type：Research paper (international conference proceedings)   Publisher：AIP Publishing  

DOI： 10.1063/5.0095596

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s42005-022-00801-w

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Other Link： https://www.nature.com/articles/s42005-022-00801-w

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Multi-tracer imaging can provide useful information in the definitive diagnosis and research of medical, biological, and pharmaceutical sciences. Single-photon emission computed tomography (SPECT) is one of the nuclear medicine imaging modalities widely used for diagnosis or medical research and has a multi-tracer imaging capability. One of the drawbacks of multi-tracer imaging is crosstalk from other gamma rays, which affects the reconstructed image. Scattering correction methods, such as the dual- and triple-energy window methods, are used for conventional SPECT imaging to reduce the background caused by the crosstalk. This study proposes another crosstalk reduction method. Some nuclides emit two or more gamma rays through intermediate levels. Thus, detecting these gamma rays with the coincidence method allows us to distinguish a true gamma ray signal and a background signal. The nuclide position can be estimated at the intersection of two gamma rays using collimators. We demonstrate herein simultaneous ¹¹¹In and ¹⁷⁷Lu imaging via the double-photon coincidence method using GAGG detectors and parallel hole collimators. The double-photon coincidence method greatly reduces the background caused by other gamma rays and offers higher-quality images than does conventional imaging.

DOI： 10.1038/s41598-021-92583-4

PubMed

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Other Link： http://www.nature.com/articles/s41598-021-92583-4

Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/nss/mic44867.2021.9875816

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Positron-emission tomography (PET) and single-photon-emission computed tomography (SPECT) are well-established nuclear-medicine imaging methods used in modern medical diagnoses. Combining PET with ¹⁸F-fluorodeoxyglucose (FDG) and SPECT with an ¹¹¹In-labelled ligand provides clinicians with information about the aggressiveness and specific types of tumors. However, it is difficult to integrate a SPECT system with a PET system because SPECT requires a collimator. Herein, we describe a novel method that provides simultaneous imaging with PET and SPECT nuclides by combining PET imaging and Compton imaging. The latter is an imaging method that utilizes Compton scattering to visualize gamma rays over a wide range of energies without requiring a collimator. Using Compton imaging with SPECT nuclides, instead of the conventional SPECT imaging method, enables PET imaging and Compton imaging to be performed with one system. In this research, we have demonstrated simultaneous in vivo imaging of a tumor-bearing mouse injected with ¹⁸F-FDG and an ¹¹¹In-antibody by using a prototype Compton-PET hybrid camera. We have succeeded in visualizing accumulations of ¹⁸F-FDG and ¹¹¹In-antibody by performing PET imaging and Compton imaging simultaneously. As simultaneous imaging utilizes the same coordinate axes, it is expected to improve the accuracy of diagnoses.

DOI： 10.1038/s41598-021-97302-7

PubMed

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Other Link： https://www.nature.com/articles/s41598-021-97302-7

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2021.165568

Scopus

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tns.2021.3086799

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tns.2021.3084144

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Radioisotope Association  

DOI： 10.3769/radioisotopes.70.271

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DOI： 10.1016/j.apradiso.2021.109864

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nima.2020.164118

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DOI： 10.1109/tns.2020.2975296

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1748-0221/15/02/c02010

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Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/15/02/C02010

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nima.2018.10.177

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nima.2018.11.141

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/sii46433.2020.9025865

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Authorship：Lead author,　Corresponding author  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.cgd.9b00706

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/sii.2019.8700440

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/1748-0221/13/01/c01040

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Authorship：Lead author,　Corresponding author  

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Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/1748-0221/12/12/c12055

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