• Title, Summary, Keyword: 감쇠보정인자

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Determination of Attenuation Collection Methods According to the Type of Radioactive Waste Drums (방사성폐기물드럼 종류별 감쇠보정방법의 결정)

  • Kwak, Sang-Soo;Choi, Byung-I1;Yoon, Suk-Jung;Lee, Ik-Whan;Kang, Duck-Won;Sung, Ki-Bang
    • Journal of Radiation Protection and Research
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    • v.22 no.4
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    • pp.309-317
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    • 1997
  • The measured radioactivity of gamma-emitting radionuclides in each radioactive waste drum using the non-destructive waste assay method is underestimated than real radioactivity in radioactive waste drum because the gamma-rays are attenuated within the medium. Therefore, the measured radioactivity should be corrected for the attenuation of gamma-rays. For the correction of the attenuation of gamma-rays, the attenuation correction method should be applied differently by considering the distribution and density of medium in radioactive wastes drum generated from nuclear power plants. In this study, the model drums were fabricated for simulating five types of radioactive waste drums generated from nuclear power plant and the optimum methods of the attenuation correction were experimentally determined to analyze the activity of radionuclides in the waste drum accurately using the segmented gamma scanning system. With the determination of the attenuation correction methods from the experimental results the transmission method and the average density method for the miscellaneous waste drum, the transmission method and the differential peak absorption method for the shielded miscellaneous waste drum were used to measure the density of medium in waste drums. Also, the average density method and the differential peak absorption method for the spent resin drum, the paraffin solidified drum, and the spent filter drum were used.

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Impact of Contrast agent for Attenuation Correction Using CT Scan in PET/CT System (PET/CT 시스템에서 CT 영상을 이용한 감쇠 보정 시 조영제가 PET 영상에 미치는 영향)

  • Son, Hye-Kyung;Turkington, Timothy G;Kwon, Yun-Young;Bong, Jung-Kyun;Jung, Hai-Jo;Kim, Hee-Joung
    • Proceedings of the Korean Society of Medical Physics Conference
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    • pp.100-103
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    • 2004
  • Experiments and simulation were done to study the impact of contrast agent when CT scan was used to attenuation correction for PET images in PET/CT system. Whole body phantom was imaged with various concentration of iodine-based contrast agent using CT. Mathematical emission and transmission density map with liver were made to simulate for whole body FDG imaging. Various transmission density maps was generated with non-uniform enhancement of contrast agent, hypo-attenuating of contrast agent for tumor, different concentration of contrast agent, and so on. Attenuation correction was done with all transmission maps. In the experiments, we confirmed that attenuation coefficient was changed by concentration of contrast agent. From the simulation data, image quality of attenuation corrected images was affected by contrast agent and artifact was produced by contrast agent. These results indicated that the contrast agent should be used with a full understanding of its potential problem in PET/CT system.

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The effects of physical factors in SPECT (물리적 요소가 SPECT 영상에 미치는 영향)

  • 손혜경;김희중;나상균;이희경
    • Progress in Medical Physics
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    • v.7 no.1
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    • pp.65-77
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    • 1996
  • Using the 2-D and 3-D Hoffman brain phantom, 3-D Jaszczak phantom and Single Photon Emission Computed Tomography, the effects of data acquisition parameter, attenuation, noise, scatter and reconstruction algorithm on image quantitation as well as image quality were studied. For the data acquisition parameters, the images were acquired by changing the increment angle of rotation and the radius. The less increment angle of rotation resulted in superior image quality. Smaller radius from the center of rotation gave better image quality, since the resolution degraded as increasing the distance from detector to object increased. Using the flood data in Jaszczak phantom, the optimal attenuation coefficients were derived as 0.12cm$\^$-1/ for all collimators. Consequently, the all images were corrected for attenuation using the derived attenuation coefficients. It showed concave line profile without attenuation correction and flat line profile with attenuation correction in flood data obtained with jaszczak phantom. And the attenuation correction improved both image qulity and image quantitation. To study the effects of noise, the images were acquired for 1min, 2min, 5min, 10min, and 20min. The 20min image showed much better noise characteristics than 1min image indicating that increasing the counting time reduces the noise characteristics which follow the Poisson distribution. The images were also acquired using dual-energy windows, one for main photopeak and another one for scatter peak. The images were then compared with and without scatter correction. Scatter correction improved image quality so that the cold sphere and bar pattern in Jaszczak phantom were clearly visualized. Scatter correction was also applied to 3-D Hoffman brain phantom and resulted in better image quality. In conclusion, the SPECT images were significantly affected by the factors of data acquisition parameter, attenuation, noise, scatter, and reconstruction algorithm and these factors must be optimized or corrected to obtain the useful SPECT data in clinical applications.

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Impact of Contrast Agent for PET Images with CT-based Attenuation Correction (CT 영상을 이용한 감쇠 보정 시 조영제가 PET 영상에 미치는 영향)

  • Son Hye-Kyung;Turkington Timothy G.;Kwon Yun-Young;Jung Haijo;Kim Hee-Joung
    • Progress in Medical Physics
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    • v.16 no.4
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    • pp.192-201
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    • 2005
  • Experiments and simulation were done to study the impact of contrast agent when CT scan was used to attenuation correction for PET Images in PET/CT system. Whole body phantom was imaged with various concentration of iodine-based contrast agent using CT. Mathematical emission and transmission density map with liver were made to simulate for whole body FDG Imaging. A variety of factors were estimated, including non-uniform enhancement of contrast agent, concentration and distribution size of contrast agent, noise level, image resolution, reconstruction algorithm, hypo-attenuation of contrast agent, and different time phases for contrast agent. Experimental studies showed that Hounsfield unit depends on the concentration of contrast agent and tube voltage. From the simulation data, contrast agents Introduced artifacts and degraded image quality on the attenuation-corrected PET images. The severity of these effects depends on a variety of factors, including the concentration and distribution size of contrast agent, the noise levels, and the Image resolution. These results Indicated that the impact of contrast agents should be considered with a full understanding of their potential problems in clinical PET/CT images.

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Measurement of Absorbed Dose at the Tissue Surface from a Plain $^{90}Sr+^{90}Y$ Beta Sources (조직 표면에서의 베타선 흡수선량 측정)

  • Hah, Suck-Ho;Kim, Jeong-Mook;Yook, Chong-Chul
    • Journal of Radiation Protection and Research
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    • v.16 no.2
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    • pp.17-26
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    • 1991
  • Beta ray $(^{90}Sr+^{90}Y)$ absorbed dose at tissue surface was measured from the distance of 30cm by use of extrapolation chamber. In the measurement, following factors were considered: effective area of collecting electrode, polarity effect, ion recombination and window attenuation. The measured absorbed dose rate at tissue surface was $1.493{\mu}Gy/sec$ with ${\pm}2.9%$.

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Calculations of Radiation Measurement-Related Correction Factors (방사선 측정관련 보정인자 계산)

  • Shin, Hee-Sung;Ro, Seung-Gy;Kim, Ho-Dong
    • Journal of Radiation Protection and Research
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    • v.28 no.1
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    • pp.19-24
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    • 2003
  • The self-attenuation factor for an $^{198}Au$ sample and the 0.412 MeV gamma-ray penetration ratio in the circular Al-cover of the radiation detector have been determined using an analytical solution and MCNP code. The results show that the self-attenuation factors obtained from the analytical solution coincide with those of MCNP code for all but the Au sample with the relatively larger radius. Then the maximum difference between the two methods appears to be 9 % in the Au sample of 1.5 mm radius. It also is revealed that the analytical solutions of the 0.412 MeV gamma-ray penetration ratio in the Al-cover of 7.62 cm radius are consistent with those of the MCNP code within the standard deviation.

A Consideration on the Electromagnetic Properties of Road Pavement Using Ground Penetrating Radar (GPR) (지표투과레이더(GPR)에 의한 도로포장의 전자기적 특성값 고찰)

  • Rhee, Jiyoung;Shim, Jaewon;Lee, Sangrae;Lee, Kang-Hyun
    • Journal of The Korean Society of Civil Engineers
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    • v.40 no.3
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    • pp.285-294
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    • 2020
  • This study investigated the use of Ground Penetrating Radar (GPR) over a two-decade period on public roads, focusing on the electromagnetic characteristics of the pavement dielectrics and attenuation. From the results, a typical range of characteristic value, influencing factors, and a correction method were suggested. The typical dielectrics of asphalt pavements were 4-7, as measured by an air-coupled 1 GHz GPR antenna. The dielectrics of concrete pavements were very large in the early age, but were drastically reduced with ageing. Ten years on, collection was in the range of 6-12. The dielectrics were proportional to the relative humidity (R.H.) of the atmosphere. The effects were reduced to one eighth with an overlay. Attenuation generally increased with thickness of the road layer, and also increased where there was damage. The GPR results could also vary depending on the weather conditions as well as on the characteristics of the GPR equipment, even at the same frequency. Therefore, GPR surveys should be performed on road surfaces without debris on a single, fine day. The reliability of the GPR analysis could be improved by cores and equipment calibration with other non-destructive test surveys.

Estimation of Variability for Complex Modulus of Rubber Considering Temperature and Material Uncertainties (온도와 물성의 불확실성을 고려한 고무의 복소계수 변동성 평가)

  • Lee, Doo-Ho;Hwang, In-Sung
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.362-365
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    • 2011
  • 본 논문에서는 통계적인 방법을 이용하여 점탄성 제진재인 합성고무의 물성에 대한 변동성을 평가하는 방법을 제안하고 측정데이터를 이용하여 합성고무에 대한 평가를 수행하였다. 고무 물성의 불확실성 인자로는 외기 온도의 변화와 실험 데이터의 오차 및 점탄성 제진모델의 오차를 고려하였다. 고무는 분수차 미분 모델로 표현되었고 온도의 영향은 비선형 이동계수모델을 도입하여 복소계수로 나타내어 동강성과 감쇠를 표현하였다. 이러한 물성모델을 바탕으로 고무에 대한 물성 실험데이터와 물성계수의 확률밀도함수 사이에 정의된 우도함수를 최대화하는 통계적 보정방법을 이용하여 물성모델의 물질계수들에 대한 변동성을 추정하였다.

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Correlation analysis of suspended sediment concentration and acoustic backscatter intensity (음파 후방산란강도와 부유사 농도의 상관관계 분석)

  • Park, JJi-Youn;Ryu, Hong Ryul;Kim, Dong-Ho;Hwang, Kyu-Nam
    • Proceedings of the Korea Water Resources Association Conference
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    • pp.282-287
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    • 2019
  • 본 연구의 목적은 음파를 이용하는 유속계로부터 관측된 후방산란강도와 실측된 부유사농도의 상관관계를 해석하여, 두 인자 사이의 관련 매개변수를 정량적으로 산정하고 관계식을 도출하는데 있다. 이를 위해 층별 유속계인 Aquadopp Profiler를 사용하여 사질 퇴적물 및 고령토 부유퇴적물 관측센서 검보정 챔버 실험을 수행하였다. 두 인자의 상관관계는 선형회귀분석을 통해 해석하였으며 그 결과로 도출된 접합곡선의 기울기는 각각 안목 A1 이 2.065, 안목 A2가 1.576, 고령토시료일 때 2.588의 값을 갖는데 이러한 차이는 시료 특성으로 설명될 수 있다. 서로 다른 입경을 갖는 시료는 후방산란 민감도에 차이가 있으며 이러한 영향으로 두 시료에서 산정된 계수 값에 차이가 발생한다. 본 연구를 통하여 도출된 측정 결과들은 후방산란강도에 미치는 수층 부유입자들의 영향이 매우 큼을 잘 보여준다. 일반적으로 수층 부유입자는 저면 퇴적물이 부유된 것으로 간주될 수 있으며, 또한 저면 퇴적물은 각 해역별로 site-specific 하다고 할 수 있다.

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