• Nuclear Engineering and Technology
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• 제56권1호
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• pp.56-63
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• 2024

In high radiation fields, gamma cameras suffer from pulse pile-up, resulting in poor energy resolution, count losses, and image distortion. To overcome this problem, various methods have been introduced to reduce the size of the aperture or pixel, reject the pile-up events, and correct the pile-up events, but these technologies have limitations in terms of mechanical design and real-time processing. The purpose of this study is to develop a real-time gamma camera to evaluate the radioactive contamination in high radiation fields. The gamma camera is composed of a pinhole collimator, NaI(Tl) scintillator, position sensitive photomultiplier (PSPMT), signal processing board, and data acquisition (DAQ). The pulse pile-up is corrected in real-time with a field programmable gate array (FPGA) using the start time correction (STC) method. The STC method corrects the amplitude of the pile-up event by correcting the time at the start point of the pile-up event. The performance of the gamma camera was evaluated using a high dose rate ¹³⁷Cs source. For pulse pile-up ratios (PPRs) of 0.45 and 0.30, the energy resolution improved by 61.5 and 20.3%, respectively. In addition, the image artifacts in the ¹³⁷Cs radioisotope image due to pile-up were reduced.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1406-1416
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• 2019

In this research, a multi-slit prompt-gamma camera was developed to locate the distal dose falloff of the proton beam spots in spot scanning proton therapy. To see the performance of the developed camera, therapeutic proton beams were delivered to a solid plate phantom and then the prompt gammas from the phantom were measured using the camera. Our results show that the camera locates the 90% distal dose falloff (= d90%), within about 2-3 mm of error for the spots which are composed $3.8{\times}10^8$ protons or more. The measured location of d90% is not very sensitive to the irradiation depth of the proton beam (i.e., the depth of proton beam from the phantom surface toward which the camera is located). Considering the number of protons per spot for the most distal spots in typical treatment cases (i.e., 2 Gy dose divided in 2 fields), the camera can locate d90% only for a fraction of the spots depending on the treatment cases. However, the information of those spots is still valuable in that, in the multi-slit prompt-gamma camera, the distal dose falloff of the spots is located solely based on prompt gamma measurement, i.e., not referring to Monte Carlo simulation.

• 한국의학물리학회지:의학물리
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• 제6권1호
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• pp.65-77
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• 1995

A new gamma camera using a-Si : H photodetectors has been designed for the imaging of heart and other small organs. In this new design the photomultiplier tubes and the position sensing circuitry are replaced by 2-D array of a-Si : H p-i-n pixel photode tectors and readout circuitry which are built on a substrate. Without the photomultiplier tubes this camera is light weight, hence can be made portable. To predict the characteristics and the performance of this new gamma camera we did Monte Carlo simulations. In the simulations 128${\times}$128 imaging array of various pixel sixes were used. $\^$99m/Tc(140keV)and $\^$201/Tl(70keV) were used as radiation sources. From the simulations we could obtain the resolution of the camera and ther overall system, and the blurring effects due to scattering in the phantom. Using the Wiener filter for image processing, restoration of the blurred image could be achieved. Simulation results of a-Si : H based gamma camera were compared with those of a conwentional gamma camera.

• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2873-2878
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• 2023

The purpose of this study is to perform radiation monitoring by acquiring gamma images and real-time optical images for ^99mTc vial source using charge couple device (CCD) cameras equipped with the proposed compact gamma camera. The compact gamma camera measures 86×65×78.5 mm³ and weighs 934 g. It is equipped with a metal 3D printed diverging collimator manufactured in a 45 field of view (FOV) to detect the location of the source. The circuit's system uses system-on-chip (SoC) and field-programmable-gate-array (FPGA) to establish a good connection between hardware and software. In detection modules, the photodetector (multi-pixel photon counters) is tiled at 8×8 to expand the activation area and improve sensitivity. The gadolinium aluminium gallium garnet (GAGG) measuring 0.5×0.5×3.5 mm³ was arranged in 38×38 arrays. Intrinsic and extrinsic performance tests such as energy spectrum, uniformity, and system sensitivity for other radioisotopes, and sensitivity evaluation at edges within FOV were conducted. The compact gamma camera can be mounted on unmanned equipment such as drones and robots that require miniaturization and light weight, so a wide range of applications in various fields are possible.

• 대한방사선기술학회지:방사선기술과학
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• 제5권1호
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• pp.71-75
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• 1982

• 한국의학물리학회지:의학물리
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• 제13권1호
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• pp.37-43
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• 2002

방사선원과 감마카메라 사이에 위치한 산란매질의 종류, 두께 그리고 조준기 종류가 감마카메라 영상에 미치는 영향을 고찰하기 위하여 실험과 시뮬레이션을 수행하였다. 감마카메라는 조준기, NaI(T1) 섬광결정(60$\times$60$\times$6 ㎣), 위치민감형 광전자증배관(PSPMT), NIMs, 제어용 컴퓨터를 사용하여 개발하였다. 시뮬레이션은 산란매질(아크릴매질/공기)의 두께 변화(0～8 cm)와 조준기의 종류(평행구멍형조준기/확산형조준기) 변화에 따라 계산하였으며 실험 역시 시뮬레이션과 같은 조건으로 수행하였다. 시뮬레이션 결과를 보면, 매질의 두께가 0 cmn에서 8 cm로 증가하면, 계수율은 평행구멍형조준기의 경우 17%(공기), 60%(아크릴) 감소하였으며 확산형 조준기의 경우 감소율이 더 심하여 각각 86%(공기), 98%(아크릴)의 계수율 감소를 보였다. 실제 실험 결과도 시뮬레이션 결과와 비슷하게 매질의 두께가 0 cm에서 8 cm로 증가하면 평행구멍형조준기의 경우 계수율은 10%(공기), 54%(아크릴) 감소하였으며 확산형조준기의 경우 36%(공기), 63%(아크릴)의 계수율 감소를 보였다. 영상의 공간분해능 역시 매질의 두께가 증가할수록 저하되었다. 연구결과 소형 감마카메라를 임상적으로 사용하고자 할 때 감마카메라를 질환 부위에 최대한 밀착시키고 산란매질 두께를 최소화해야 고효율, 고분해능 영상을 얻을 수 있음을 확인하였다.

• Journal of Radiation Protection and Research
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• 제29권4호
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• pp.257-261
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• 2004

핀홀 감마카메라의 민감도를 향상시키기 위하여 픽셀화된 CsI(Tl) 섬광체와 위치민감형 광증배관을 이용하여 부호화 구경 감마카메라를 개발하였다. Rounded-hole로 이루어진 $13{\times}11$ 픽셀구조의 개조된 uniformly reductant array (URA) 가 계측기의 공간해상도를 고려하여 부호화된 마스크로 선택되었다. 부호화된 구경 카메라와 핀홀 카메라의 성능을 비교하기 위하여 Tc-99m 소스의 여러 가지 형태를 이용하여 테스트 하였으며, 신호 대 잡음비 또는 민감도의 향상에 대한 카메라의 성능을 분석하였다. 그 결과 공간해 상도에 있어서 약간의 저하가 있었으나 영상의 질은 매우 향상되었다. 비록 카메라의 개발과 테스트가 저에너지 영역에서 이루어졌지만, 부호화 구경 카메라의 구상은 방사성 물질 감시 그리고 다른 응용들에 있어서도 효과적으로 사용되어질 수 있을 것이다.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3422-3428
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• 2022

The prompt gamma imaging (PGI) technique is considered as one of the most promising approaches to estimate the range of proton beam in the patient and unlock the full potential of proton therapy. In the PGI technique, a dedicated algorithm is required to estimate the range of the proton beam from the prompt gamma (PG) distribution acquired by a PGI system. In the present study, a new range estimation algorithm was developed for a multi-slit prompt-gamma camera, one of PGI systems, to estimate the range of proton beam with high accuracy. The performance of the developed algorithm was evaluated by Monte Carlo simulations for various beam/phantom combinations. Our results generally show that the developed algorithm is very robust, showing very high accuracy and precision for all the cases considered in the present study. The range estimation accuracy of the developed algorithm was 0.5-1.7 mm, which is approximately 1% of beam range, for 1×10⁹ protons. Even for the typical number of protons for a spot (1×10⁸), the range estimation accuracy of the developed algorithm was 2.1-4.6 mm and smaller than the range uncertainties and typical safety margin, while that of the existing algorithm was 2.5-9.6 mm.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1998년도 추계학술대회
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• pp.303-304
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• 1998

We investigated the effects of scintillation crystal surface treatment on gamma camera imaging. The NaI(Tl) and CsI(Tl) (20 mm (dia.) $\times10mm$ (thick) plate) scintillators were chosen for this study. Two different surface treatments, white and black reflectors, were applied to NaI(Tl) and CsI(Tl). The optical properties of generated scintillation light were evaluated using Monte Carlo simulation and postion sensitive photo multiplier tube (PSPMT). We measured sensitivity, energy resolution and spatial resolution of a gamma camera system with the scintillators coupled to a PSPMT. Based on the results, we concluded that the careful consideration of surface treatments of the scintillator was necessary in order to develop the gamma camera having good sensitivity and spatial resolution.

• Nuclear Engineering and Technology
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• 제51권2호
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• pp.533-538
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• 2019

The mechanical-collimation imaging is the most mature technology in prompt gamma (PG) imaging which is considered the most promising technology for beam range verification in proton therapy. The purpose of the present study is to compare the performances of two mechanical-collimation PG cameras, knife-edge (KE) camera and multi-slit (MS) camera. For this, the PG cameras were modeled by Geant4 Monte Carlo code, and the performances of the cameras were compared for imaginary point and line sources and for proton beams incident on a cylindrical PMMA phantom. From the simulation results, the KE camera was found to show higher counting efficiency than the MS camera, being able to estimate the beam range even for $10^7$ protons. Our results, however, confirmed that in order to estimate the beam range correctly, the KE camera should be aligned, at least approximately, to the location of the proton beam range. The MS camera was found to show lower efficiency, being able to estimate the beam range correctly only when the number of the protons is at least $10^8$. For enough number of protons, however, the MS camera estimated the beam range correctly, errors being less than 1.2 mm, regardless of the location of the camera.