• Progress in Medical Physics
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• v.25 no.2
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• pp.65-71
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• 2014

A Varian Portal Dosimetry system was compared to an isocentrically mounted MapCHECK 2 diode array for volumetric modulated arc therapy (VMAT) QA. A Varian TrueBeam STx with an aS-1000 digital imaging panel was used to acquire VMAT QA images for 13 plans using four photon energies (6, 8, 10 and 15 MV). The EPID-based QA images were compared to the Portal Dose Image Prediction calculated in the Varian Eclipse treatment planning system (TPS). An isocentrically mounted Sun Nuclear MapCHECK 2 diode array with 5 cm water-equivalent buildup was also used for the VMAT QAs and the measurements were compared to a composite dose plane from the Eclipse TPS. A ${\gamma}$ test was implemented in the Sun Nuclear Patient software with 10% threshold and absolute comparison at 1%/1 mm (dose difference/distance-to-agreement), 2%/2 mm, and 3%/3 mm criteria for both QA methods. The two-tailed paired Student's t-test was employed to analyze the statistical significance at 95% confidence level. The average ${\gamma}$ passing rates were greater than 95% at 3%/3 mm using both methods for all four energies. The differences in the average passing rates between the two methods were within 1.7% and 1.6% of each other when analyzed at 2%/2 mm and 3%/3 mm, respectively. The EPID passing rates were somewhat better than the MapCHECK 2 when analyzed at 1%/1 mm; the difference was lower for 8 MV and 10 MV. However, the differences were not statistically significant for all criteria and energies (p-values >0.05). The EPID-based QA showed large off-axis over-response and dependence of ${\gamma}$ passing rate on energy, while the MapCHECK 2 was susceptible to the MLC tongue-and-groove effect. The two fluence-based QA techniques can be an alternative tool of VMAT QA to each other, if the limitations of each QA method (mechanical sag, detector response, and detector alignment) are carefully considered.

• Journal of Astronomy and Space Sciences
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• v.31 no.1
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• pp.67-72
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• 2014

The next generation small satellite-1 (NEXTSat-1) program has been kicked off in 2012, and it will be launched in 2016 for the science missions and the verification of space core technologies. The payloads for these science missions are the Instrument for the Study of Space Storms (ISSS) and NIR Imaging Spectrometer for Star formation history (NISS). The ISSS and the NISS have been developed by Korea Advanced Institute of Science and Technology (KAIST) and Korea Astronomy and Space science Institute (KASI) respectively. The ISSS detects plasma densities and particle fluxes of 10 MeV energy range near the Earth and the NISS uses spectrometer. In order to verify the spacecraft core technologies in the space, the total of 7 space core technologies (SCT) will be applied to the NEXTSat-1 for space verification and those are under development. Thus, the operation modes for the ISSS and the NISS for space science missions and 7 SCTs for technology missions are analyzed for the required operation time during the NEXTSat-1's mission life time of 2 years. In this paper, the operational concept of the NEXTSat-1's science missions as well as the verification of space core technologies are presented considering constraints of volume, mass, and power after launch.

• Progress in Medical Physics
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• v.5 no.1
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• pp.3-12
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• 1994

Purporse : It is known that detection of calcification by MRI is difficulty in intracranial calcified lesions, but author tried to evaluate the signal intensity image of calcification by MR with experimental model. Subjects & Methods : Author analyzed and compared with values of calcium carbonate and hydroxyapatite phantoms by each concentration (10, 20, 30, 40, 50%) and size(1-10mm), measured ROI attenuating from CT and MRI(TlWI & T2WI). Results : The high concentration of calcium carbonate is, the lower the signal intensity of calcium carbonate phantom is both T1 & T2WI. For concentration of Hydroxyapatite of up to 30% by weight the signal intensity on standard T1 weighted images increased but subsequently decreased. Hyperintensity does not preclude calcification as a cause of the signal alteration-an observation that all radiologists interpreting MR images need to be aware of. Conclusion: The signal intensity of intracranial calcification is various on MR imaging in concerning with components, concentration, & size of calcification, and especially high signal intensity of intracranial calcification noted differencial diagnosis.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.47-47
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• 2003

Abstract: RF Birdcage Resonator는 높은 자장 균질성과 신호 대 잡음비의 특성이 좋음으로 인해 MRI와 MRS 연구에 보편적으로 사용되고 있다. 본 연구는 인체를 비롯한 동물실험을 위한 다양한 실험대상에 따라 코일의 크기를 예측하여 Birdcage Resonator를 개발하였다. Unloaded와 Loaded 상태에서의 전기적인 성향을 Lumped Element Circuit Theory를 따라 일반적인 분석을 하였을 뿐 아니라 실제적인 실험을 통한 분석도 하였다. Introduction: Birdcage Resonator 는 자장 균일성이 뛰어나고 신호대잡음비가 좋아 Magnetic Resonance Imaging과 Spectroscopy에 유용하게 사용되어지고 있다. 이 연구에서는 실험대상에 따른 여러 가지의 Birdcage Resonator를 개발하기 위해 Lumped Element Circuit Theory를 사용한 일반적인 이론적 방법론을 이용하여 코일을 분석하였을 뿐 아니라 실제 제작한 후 실험을 통한 실질적인 영상분석도 병행하여 진행하였다. Method: 실질적인 개발에 앞서 Lumped Element Circuit Theory를 통해 이론적인 분석으로부터 나온 여러 parameter들을 정리하였다. 제작 후 실험적인 분석은 Network Analyzer (HP 4195A, 미국)를 통한 1차적인 분석을 한 후 최종적으로 3T MRI 장비 (메디너스, 한국)에서 수행하였다. 제작된 Birdcage Resonator의 종류는 기본적으로 Low-Pass Filter를 적용한 12-column 구조이다. 각각의 직경과 element의 길이는 다음과 같다. 1) 직경 13cm, element의 길이 22cm, 2) 직경 15cm, element의 길이 22cm, 3) 직경 17 cm, element의 길이 25cm. Result and Discussion: 여러 parameter들을 이론적으로 계산하여 실제 Birdcage Resonator를 제작하여 실험적인 분석을 한 결과 많은 차이가 있음을 알 수 있었다. 그 이유는 이론적인 계산에서는 생각되지 않았던 요인들이 실제 제작에 있어서는 많은 영향을 미쳤기 때문인 것이다. Network Analyzer를 통한 1차적인 분석 후에도 실제의 Magnet Field내에서 또 다시 차이가 나는 것 또한 같은 이유에서이다. 그러므로 Birdcage Resonator 제작에 있어서 이러한 여러 요인들을 충분히 고려하여야 할 것이다. Acknowledgement: 본 연구는 2002 년도 한국과학재단 목적기초연구사업 (과제번호 : R0l-2002-000-00294-0 (2002) 지원아래 수행되었다.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.48-48
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• 2003

Abstract: 현대 질병의 최종진단은 세포수준의 해부형태학적 연구가 일반적이며 광학현미경이나 전자현미경을 이용한 병리조직학적 소견을 바탕으로 진단되어지고 있다. 이러한 진단에는 In vivo 검사가 거의 불가능하여 주로 생검을 통한 연구만 수행되고 있어 진단함에 있어 단계적인 불편이 초래될 뿐만 아니라 악성 종양의 전이를 유발시킬 수 있고 또한 생리 및 생화학적 분석이 어렵다. 이러한 문제점을 해결하기 위해 고분해능의 RF Surface Coil을 개발하여 In vivo 및 비침습적인 방법인 MR Technology를 이용하고자 한다. Introduction: 피부조직과 같은 미세 인체구조 연구를 위해 고해상도 3T MRI 시스템에 적합한 고분해능의 RF surface coil을 개발하고 있다. In vivo 연구를 위한 여러 parameter를 최적화하여 기능영상에도 부합된다. 비침습적인 In vivo 검사에 의한 세포수준의 극 미세구조의 연구가 가능해짐으로써 과거 시행하던 침습적인 생검없이 각종질환의 진단적 접근이 병리학적 수준으로 향상되어 질병의 정확한 진단이 가능해지게 될 것이다. Method: 고분해능의 RF Surface Coil을 제작하여 3T MR 장비에서 피부 미세구조연구에 보다 적합하도록 In vivo 및 In vitro 실험을 수행하였다. In vitro 실험은 In vivo 연구를 위한 여러 parameter들을 최적화하기 위한 기초 실험을 하였고 다양한 팬톰들을 이용하여 Tl 강조영상, T2 강조영상을 획득하였으며, SNR을 높이기 위한 개선에 대한 연구를 수행하였다. In vivo 실험은 정상피부에서 다양한 부위에 대한 피부영상의 예비 연구를 수행하였다. Result and Discussion: 비침습적인 In vivo 검사에 의한 세포수준의 극 미세구조의 연구가 가능해짐으로써 과거 시행하던 침습적인 생검없이 각종질환의 진단적 접근이 병리학적 수준에서 가능해짐으로써 질병의 정확한 진단이 가능해지게 될 것이다. Acknowledgement: 본 연구는 2002 년도 한국과학재단 목적기초연구사업 (과제번호 : R0l-2002-000-00294-0 (2002)) 지원아래 수행되었다.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.104-107
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• 2004

In this study, using brain phantom for multi-modality imaging, we acquired CT, MR and PET images and performed registration of these anatomical images and nuclear medicine functional images. The algorithms and program applied for registration were Chamfer Matching and Mutual Information Maximization algorithm which have been using frequently in clinic and verified accuracy respectively. In result, both algorithms were useful methods for CT-MR, CT-PET and MR-PET. But Mutual Information Maximization was more effective algorithm for low resolution image as nuclear medicine functional image.

• Progress in Medical Physics
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• v.21 no.1
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• pp.42-51
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• 2010

Imaging studies using MRI, PET, and/or MEG have been primary evaluation methods to quantitatively assess cognitive function. Recent advances in computational technology and information technology may allow a novel evaluation methodology to quantitate cognitive function more cost-effectively. In this study, we developed a software package composed of a series of tests to evaluate cognitive ability combined with a user-friendly touch screen input device. This cognitive assessment tool can quantitate concentration, numeric memory, associative memory, topological memory, visual and muscular reaction, and acoustic reaction over a relatively short testing time. We performed an empirical study on eighty normal subjects aged 20 and 59 years old using the developed evaluation methods. Age-related cognitive deterioration after 40 years old was confirmed. There was no difference in cognitive ability between male and female in the same age group. This study demonstrates the feasibility of a simple but effective evaluation software tool to quantitatively assess cognitive ability. This methodology may provide improved accessibility and reduced costs to perform cognitive function studies to compare between various subject groups.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1277-1281
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• 2020

A novel ceramic Gas Electron Multiplier (GEM) has been developed to meet the demand of high counting rate for the neutron detection which is an alternative to ³He-based detector at China Spallation Neutron Source (CSNS). An experiment was performed to measure the neutron transmittance of ceramic-GEM and FR4-GEM at the small angle neutron scattering (SANS) instrument. The result showed the ceramic-GEM has higher transmittance and less self-scattering especially for cold neutrons. One single ceramic GEM could give a gain of 10²-10⁴ in the mixture gas of Ar and CO₂ (90%:10%) and its energy resolution was about 27.7% by using ⁵⁵Fe X ray of 5.9 keV. A prototype has been developed in order to investigate the performances of the ceramic GEM-based neutron detector. Several neutron beam tests, including detection efficiency, spatial resolution, two-dimensional imaging, and wavelength spectrum, were carried out at CSNS and China Mianyang Research Reactor (CMRR). The results show that the ceramic GEM-based neutron detector is a good candidate to measure the high intensity neutrons.

• Progress in Medical Physics
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• v.19 no.3
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• pp.186-190
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• 2008

In this study, we describe the preliminary application for the delineation of a metal object using cone-beam reconstruction (CBR) based on limited electronic portal imaging device (EPID) projections. A typical Feldkamp, Davis and Kress (FDK) reconstruction algorithm accompanying the edge preserving smoothing filter was used as only a few projections are acquired for reconstruction. In a correlation study of the projection numbers, we found that the size of the seeds and their location depicted by these CBR images were almost identical. Limited views were used for CBR, and our method is inexpensive and competitive for use in clinical applications.

• Progress in Medical Physics
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• v.30 no.4
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• pp.160-166
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• 2019

This study examined the clinical use of two newly installed computed tomography (CT) simulators in the Department of Radiation Oncology. The accreditation procedure was performed by the Korean Institute for Accreditation of Medical Imaging. An Xi R/F dosimeter was used to measure the CT dose index for each plug of the CT dose index phantom. Image qualities such as the Hounsfield unit (HU) value of water, noise level, homogeneity, existence of artifacts, spatial resolution, contrast, and slice thickness were evaluated by scanning a CT performance phantom. All test items were evaluated as to whether they were within the required tolerance level. CT calibration curves-the relationship between CT number and relative electron density-were obtained for dose calculations in the treatment planning system. The positional accuracy of the lasers was also evaluated. The volume CT dose indices for the head phantom were 22.26 mGy and 23.70 mGy, and those for body phantom were 12.30 mGy and 12.99 mGy for the first and second CT simulators, respectively. HU accuracy, noise, and homogeneity for the first CT simulator were -0.2 HU, 4.9 HU, and 0.69 HU, respectively, while those for second CT simulator were 1.9 HU, 4.9 HU, and 0.70 HU, respectively. Five air-filled holes with a diameter of 1.00 mm were used for assessment of spatial resolution and a low contrast object with a diameter of 6.4 mm was clearly discernible by both CT scanners. Both CT simulators exhibited comparable performance and are acceptable for clinical use.