Radiation imaging with a rotational modulation collimator (RMC) coupled to a Cs2LiYCl6:Ce (CLYC) detector

Kim, Hyun Suk,Ye, Sung-Joon,Shin, Youngjun,Lee, Gyemin,Kim, Geehyun 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

<P>As an attempt to develop a gamma-ray/neutron dual-particle imager, we employed a rotating modulation collimator (RMC) coupled to a pulse shape discrimination-capable scintillator. We performed fundamental simulations on the proposed RMC system utilizing a CLYC detector to verify the basic properties of the RMC system and to optimize the computing methods for the Monte Carlo simulation. We obtained batches of modulation patterns for various source locations by using Monte Carlo N-Particle simulations, and we studied the characteristics of the modulation patterns, such as the rotational effect, the shift effect, and the symmetric effect. We compared simulated modulation patterns with those obtained from the mathematical model of the RMC system to investigate the feasibility of identifying the source location correctly based on the simulated patterns. When a source was located in the far-field region, the modulation patterns showed good agreement between the Monte Carlo simulation and the mathematical model. The results hold promises for reconstructing gamma and neutron images of radioactivity by using a RMC system on a CLYC detector.</P>

A Monte Carlo simulation study for the gamma-ray/neutron dual-particle imager using rotational modulation collimator (RMC)

Kim, Hyun Suk,Choi, Hong Yeop,Lee, Gyemin,Ye, Sung-Joon,Smith, Martin B,Kim, Geehyun IOP 2018 Journal of radiological protection Vol.38 No.1

<P>The aim of this work is to develop a gamma-ray/neutron dual-particle imager, based on rotational modulation collimators (RMCs) and pulse shape discrimination (PSD)-capable scintillators, for possible applications for radioactivity monitoring as well as nuclear security and safeguards. A Monte Carlo simulation study was performed to design an RMC system for the dual-particle imaging, and modulation patterns were obtained for gamma-ray and neutron sources in various configurations. We applied an image reconstruction algorithm utilizing the maximum-likelihood expectation-maximization method based on the analytical modeling of source-detector configurations, to the Monte Carlo simulation results. Both gamma-ray and neutron source distributions were reconstructed and evaluated in terms of signal-to-noise ratio, showing the viability of developing an RMC-based gamma-ray/neutron dual-particle imager using PSD-capable scintillators.</P>

Characterization of a CLYC Detector and Validation of the Monte Carlo Simulation by Measurement Experiments

Kim, Hyun Suk,Smith, Martin B.,Koslowsky, Martin R.,Kwak, Sung-Woo,Ye, Sung-Joon,Kim, Geehyun The Korean Association for Radiation Protection 2017 방사선방어학회지 Vol.42 No.1

Background: Simultaneous detection of neutrons and gamma rays have become much more practicable, by taking advantage of good gamma-ray discrimination properties using pulse shape discrimination (PSD) technique. Recently, we introduced a commercial CLYC system in Korea, and performed an initial characterization and simulation studies for the CLYC detector system to provide references for the future implementation of the dual-mode scintillator system in various studies and applications. Materials and Methods: We evaluated a CLYC detector with 95% $^6Li$ enrichment using various gamma-ray sources and a $^{252}Cf$ neutron source, with validation of our Monte Carlo simulation results via measurement experiments. Absolute full-energy peak efficiency values were calculated for gamma-ray sources and neutron source using MCNP6 and compared with measurement experiments of the calibration sources. In addition, behavioral characteristics of neutrons were validated by comparing simulations and experiments on neutron moderation with various polyethylene (PE) moderator thicknesses. Results and Discussion: Both results showed good agreements in overall characteristics of the gamma and neutron detection efficiencies, with consistent ~20% discrepancy. Furthermore, moderation of neutrons emitted from $^{252}Cf$ showed similarities between the simulation and the experiment, in terms of their relative ratios depending on the thickness of the PE moderator. Conclusion: A CLYC detector system was characterized for its energy resolution and detection efficiency, and Monte Carlo simulations on the detector system was validated experimentally. Validation of the simulation results in overall trend of the CLYC detector behavior will provide the fundamental basis and validity of follow-up Monte Carlo simulation studies for the development of our dual-particle imager using a rotational modulation collimator.

Digital n-γ Pulse Shape Discrimination in Organic Scintillators with a High-Speed Digitizer

Kim, Chanho,Yeom, Jung-Yeol,Kim, Geehyun The Korean Association for Radiation Protection 2019 방사선방어학회지 Vol.44 No.2

Background: As neutron fields are always accompanied by gamma rays, it is essential to distinguish neutrons from gamma rays in the detection of neutrons. Neutrons and gamma rays can be separated by pulse shape discrimination (PSD) methods. Recently, we performed characterization of a stilbene scintillator detector and an EJ-301 liquid scintillator detector with a high-speed digitizer DT5730 and investigated optimized PSD variables for both detectors. This study is for providing a basis for developing fast neutron/gamma-ray dual-particle imager. Materials and Methods: We conducted PSD experiments using stilbene scintillator and EJ-301 liquid scintillator and evaluated neutron and gamma ray discriminability of each PSD method with a $^{137}Cs$ gamma source and a $^{252}Cf$ neutron source. We implemented digital signal processing techniques to apply two PSD methods - the charge comparison (CC) method and the constant time discrimination (CTD) method - to distinguish neutrons from gamma rays. We tried to find optimized PSD variables giving the best discriminability in a given experimental condition. Results and Discussion: For the stilbene scintillator detector, the charge comparison method and the constant time discrimination method both delivered the PSD FOM values of 1.7. For the EJ-301 liquid scintillator detector, both PSD methods delivered the PSD FOM values of 1.79. With the same PSD variables, PSD performance was excellent in $300{\pm}100keVee$, $500{\pm}100keVee$, and $700{\pm}100keVee$ energy regions. This result shows that we can achieve an effective discrimination of neutrons from gamma rays using these scintillator detector systems. Conclusion: We applied both PSD methods to a stilbene and a liquid scintillator and optimized the PSD performance represented by FOM values. We observed a good separation performance of both scintillators combined with a high-speed digitizer and digital PSD. These results will provide reference values for the dual-particle imager we are developing, which can image both fast neutrons and gamma rays simultaneously.

Design and Fabrication of CLYC-Based Rotational Modulation Collimator (RMC) System for Gamma-Ray/Neutron Dual-Particle Imager

Kim, Hyun Suk,Lee, Jooyub,Choi, Sanghun,Bang, Young-bong,Ye, Sung-Joon,Kim, Geehyun The Korean Association for Radiation Protection 2021 방사선방어학회지 Vol.46 No.3

Background: This work aims to develop a new imaging system based on a pulse shape discrimination-capable Cs₂LiYCl₆:Ce (CLYC) scintillation detector combined with the rotational modulation collimator (RMC) technique for dual-particle imaging. Materials and Methods: In this study, a CLYC-based RMC system was designed based on Monte Carlo simulations, and a prototype was fabricated. Therein, a rotation control system was developed to rotate the RMC unit precisely, and a graphical user interface-based software was also developed to operate the data acquisition with RMC rotation. The RMC system was developed to allow combining various types of collimator masks and detectors interchangeably, making the imaging system more versatile for various applications and conditions. Results and Discussion: Operational performance of the fabricated system was studied by checking the accuracy and precision of the collimator rotation and obtaining modulation patterns from a gamma-ray source repeatedly. Conclusion: The prototype RMC system showed reliability in its mechanical properties and reproducibility in the acquisition of modulation patterns, and it will be further investigated for its dual-particle imaging capability with various complex radioactive source conditions.

한국인에서 전립선암을 예측하는 데 있어 Prostate Health Index Density의 임상적 유용성에 관한 전향적, 다기관 연구

송기현(Geehyun Song),박홍주(Hongzoo Park),이상욱(Sang Wook Lee),강태욱(Tae Wook Kang),정재흥(Jae Hung Jung),정현철(Hyun Chul Chung),김성진(Sung Jin Kim),박종연(Jong Yeon Park),김정현(Jeong Hyun Kim) 대한비뇨기종양학회 2020 대한비뇨기종양학회지 Vol.18 No.2

Purpose: We evaluated the clinical performance of Prostate Health Index (PHI) density with [-2]proPSA (p2PSA) and its derivatives in predicting the presence of prostate cancer (PCa) in Korean men. Materials and Methods: A total of 706 men with total prostate-specific antigen (tPSA)≥2.5 ng/mL who underwent their first prostate biopsy were included in this prospective, multicenter, observational study. Diagnostic accuracy of tPSA, free-to-total PSA ratio (%fPSA), p2PSA, %p2PSA, the Beckman Coulter PHI, and PHI density was assessed by receiver operating characteristic curve analyses and logistic regression analyses. PHI was calculated as [(p2PSA/free PSA)×tPSA½], and density calculations were performed using prostate volume as determined by transrectal ultrasonography. Results: Overall, PCa was detected in 367 of all subjects (52%). In men with tPSA 2.5-10 ng/mL, the detection rate of PCa was 41.1% (188 of 457). In this group, PHI and PHI density were the most accurate predictors of PCa and significantly outperformed tPSA and %fPSA; area under the curve for tPSA, %fPSA, %p2PSA, PHI, and PHI density was 0.58, 0.68, 0.70, 0.75, 0.73 respectively. PHI and PHI density were also the strongest predictor of PCa with Gleason score ≥7. Conclusions: Based on the present prospective multicenter experience, PHI and PHI density demonstrate the superior clinical performance in predicting the presence of PCa in Korean men with tPSA 2.5-10 ng/mL.

Radiation Imaging with a Rotational Modulation Collimator (RMC) Coupled to a Cs2LiYCl6:Ce (CLYC) Detector

Hyun Suk Kim,Sung-Joon Ye,Youngjun Shin,이계민,Geehyun Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.11

As an attempt to develop a gamma-ray/neutron dual-particle imager, we employed a rotating modulation collimator (RMC) coupled to a pulse shape discrimination-capable scintillator. We performed fundamental simulations on the proposed RMC system utilizing a CLYC detector to verify the basic properties of the RMC system and to optimize the computing methods for the Monte Carlo simulation. We obtained batches of modulation patterns for various source locations by using Monte Carlo N-Particle simulations, and we studied the characteristics of the modulation patterns, such as the rotational effect, the shift effect, and the symmetric effect. We compared simulated modulation patterns with those obtained from the mathematical model of the RMC system to investigate the feasibility of identifying the source location correctly based on the simulated patterns. When a source was located in the far-field region, the modulation patterns showed good agreement between the Monte Carlo simulation and the mathematical model. The results hold promises for reconstructing gamma and neutron images of radioactivity by using a RMC system on a CLYC detector.

Hypoxic Preconditioned Mesenchymal Stromal Cell Therapy in a Rat Model of Renal Ischemia-reperfusion Injury: Development of Optimal Protocol to Potentiate Therapeutic Efficacy

Jang, Myoung Jin,You, Dalsan,Park, Jin Young,Kim, Kyung,Aum, Joomin,Lee, Chunwoo,Song, Geehyun,Shin, Ha Chul,Suh, Nayoung,Kim, Yong Man,Kim, Choung-Soo Korean Society for Stem Cell Research 2018 International journal of stem cells Vol.11 No.2

<P>Although previous and ongoing clinical studies have used stromal cells during renal ischemia-reperfusion injury (IRI), there is little consensus regarding the optimal protocol. We aimed to optimize the protocol for hypoxic preconditioned human bone marrow-derived mesenchymal stromal cell (HP-hBMSC) therapy in a rat model of renal IRI. We determined the optimal injection route (renal arterial, renal parenchymal, and tail venous injection), dose (low-dose: 1×10<SUP>6</SUP>, moderate-dose: 2×10<SUP>6</SUP>, and high-dose: 4×10<SUP>6</SUP>), and injection period (pre-, concurrent-, and post-IRI). During optimal injection route study, renal arterial injections significantly reduced the decreasing glomerular filtration rate (GFR), as compared to GFRs for the IRI control group, 2 and 4 days after IRI. Therapeutic effects and histological recoveries were the greatest in the group receiving renal arterial injections. During the dose finding study, high-dose injections significantly reduced the decreasing GFR, as compared to GFRs for the IRI control group, 3 days after IRI. Therapeutic effects and histological recoveries were the greatest in the high-dose injection group. While determining the optimal injection timing study, concurrent-IRI injection reduced elevated serum creatinine levels, as compared to those of the IRI control group, 1 day after IRI. Pre-IRI injection significantly reduced the decreasing GFR, as compared with GFRs for the IRI control group, 1 day after IRI. Therapeutic effects and histological recoveries were the greatest in the concurrent-IRI group. In conclusion, the concurrent-IRI administration of a high dose of HP-hBMSC via the renal artery leads to an optimal recovery of renal function after renal IRI.</P>

MCNP-polimi simulation for the compressed-sensing based reconstruction in a coded-aperture imaging CAI extended to partially-coded field-of-view

Jeong, Manhee,Kim, Geehyun Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.1

This paper deals with accurate image reconstruction of gamma camera using a coded-aperture mask based on pixel-type CsI(Tl) scintillator coupled with silicon photomultipliers (SiPMs) array. Coded-aperture imaging (CAI) system typically has a smaller effective viewing angle than Compton camera. Thus, if the position of the gamma source to be searched is out of the fully-coded field-of-view (FCFOV) region of the CAI system, artifacts can be generated when the image is reconstructed by using the conventional cross-correlation (CC) method. In this work, we propose an effective method for more accurate reconstruction in CAI considering the source distribution of partially-coded field-of-view (PCFOV) in the reconstruction in attempt to overcome this drawback. We employed an iterative algorithm based on compressed-sensing (CS) and compared the reconstruction quality with that of the CC algorithm. Both algorithms were implemented and performed a systematic Monte Carlo simulation to demonstrate the possiblilty of the proposed method. The reconstructed image qualities were quantitatively evaluated in sense of the root mean square error (RMSE) and the peak signal-to-noise ratio (PSNR). Our simulation results indicate that the proposed method provides more accurate location information of the simulated gamma source than the CC-based method.

Monte Carlo Simulation for Designing a CZT-based Fork Detection System

Wooseong Hong,Geehyun Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

The detector response was simulated to design a fork detection system for verifying the characteristics of spent fuel. The fork detection system currently used consists of two fission chamber and an ion chamber, and it is nuclear safeguard equipment that measures the gross neutrons and gross gamma rays emitted from the spent fuel assembly to identify the characteristics of the spent fuel and verify the authenticity of the operation history. In order to improve the current fork detection system, we are developing a system that applies CZT, a room temperature semiconductor detector, and a stilbene detector, which is an organic scintillator. Depletion calculations were performed using the ORIGEN code to determine the radiological characteristics emitted from spent nuclear fuel assembly. The flux of radiation emitted from the spent nuclear fuel assembly was calculated by changing the conditions such as initial enrichment, burnup, and cooling time, which are major variables of spent fuel assembly. The calculated result is used as the source term of the particle transport code. Considering the general operating conditions of the pressurized light water reactor, the conditions were changed in the range of 3-5% for initial enrichment and 30-72 GWD/MTU for burnup, and the cooling time was given within 10 years. MCNP 6.2, a Monte Carlo simulation code, was used to simulate the detector response to radiation emitted from spent nuclear fuel assembly. According to the shape, size, and position of the CZT detector, the gamma counts incident on the detector were calculated and derived the initial design of our fork detection system.