• 방사선산업학회지
• /
• 제10권1호
• /
• pp.37-41
• /
• 2016

The recent prevalence of PET examinations in Korea has led to an increase in the number of cyclotrons. The medical isotope $^{18}F$ produced in most cyclotron facilities currently operating in Korea is emitted into the environment during the production of [$^{18}F$]FDG, a cancerdiagnosis reagent. The amount of [$^{18}F$]FDG synthesized determines the radioactive concentration of $^{18}F$ in the exhaust. At some facilities, this amount temporarily exceeds the emission limit. In this study, we evaluated the $^{18}F$ radioactivity concentration in the exhaust from the cyclotron facility at Chosun University. The $^{18}F$ radioactivity concentration was measured using an air sampler and a HPGe semiconductor detector. The measurements showed that the radioactive concentration of $^{18}F$ in the exhaust at the cyclotron facility at Chosun University was the highest during [$^{18}F$]FDG synthesis but remained under the legal limit of $2,000Bq\;m^{-3}$.

• 대한방사선기술학회지:방사선기술과학
• /
• 제37권4호
• /
• pp.253-259
• /
• 2014

Traveling heater method(THM) 방법을 이용하여 성장시킨 CdZnTe(CZT) 단결정 방사선 소자에 대한 고에너지(high energy) 감마선 에너지 분해능(energy resolution)을 평가하고자 $6{\times}6{\times}12mm^3$ 크기의 CZT 소자를 제작하였다. 두꺼운 방사선 소자의 경우, 전자에 비해 상대적으로 이동속도가 느린 정공(hole)으로 인해 발생하는 hole-tailing 효과가 심화되어 고에너지 영역의 에너지 분해능이 저하되는 현상이 발생한다. 전자(electron)와 정공(hole)의 두 개의 전하 운반자(charge carrier) 중에서 하나의 전하 운반자를 선택적으로 수집하여 에너지 분해능을 높이는 것이 가능하다. 가상 Frisch-그리드(virtual Frisch-grid) 소자는 소자 내부의 가중 퍼텐셜(weighting potential)을 조절하여 전자에 의한 유도전류(induced current)만을 선택적으로 이용하는 방법으로써 제작 과정과 적용이 용이하다. 본 연구에서는 THM 방법으로 성장한 큰 부피의 CZT 방사선 소자의 특성과 가상 Frisch-그리드의 효용성을 평가하였다. 가상 Frisch-그리드의 적절한 위치와 너비는 Maxwell ver.14(ANSYS, 미국)를 이용하여 모의실험으로 정하였다. $^{137}Cs$ 동위원소를 이용한 펄스 높이 스펙트럼(pulse height spectrum) 측정에서 가상 Frisch-그리드를 적용했을 때 662 keV 피크에 대해 2.2%의 에너지 분해능을 확인할 수 있었다.

• Imaging Science in Dentistry
• /
• 제39권1호
• /
• pp.27-33
• /
• 2009

Purpose: The purpose of this study was to evaluate the clinical usefulness of the recently developed multi-detector computed tomography and cone beam computed tomography in pre-operative implant evaluation, by comparing them with the single detector computed tomography, already confirmed for accuracy in this area. Materials and Methods: Five partially edentulous dry human mandibles, with $1{\times}1mm$ gutta percha cones, placed in 5mm intervals posterior to the mental foramen on each side of the buccal part of the mandible, were used in this study. They were scanned as follows: 1) Single detector computed tomography: slice thickness 1mm, 200mA, 120kV 2) Multi-detector computed tomography: slice thickness 0.75mm, 250mA, 120kV 3) Cone beam computed tomography: 15mAs, 120kV Axial images acquired from three computed tomographies were transferred to personal computer, and then reformatted cross-sectional images were generated using V-Implant $2.0^{(R)}$ (CyberMed Inc., Seoul, Korea) software. Among the cross-sectional images of the gutta perch a cone, placed in the buccal body of the mandible, the most precise cross section was selected as the measuring point and the distance from the most superior border of the mandibular canal to the alveolar crest was measured and analyzed 10 times by a dentist. Results: There were no significant intraobserver differences in the distance from the most superior border of the mandibular canal to the alveolar crest (p>0.05). There were no significant differences among single detector computed tomography, multi-detector computed tomography and cone beam computed tomography in the distance from the most superior border of the mandibular canal to the alveolar crest (p>0.05). Conclusion: Multi-detector computed tomography and cone beam computed tomography are clinically useful in the evaluation of pre-operative site for mandibular dental implants, with consideration for radiation exposure dose and scanning time.

• 한국콘텐츠학회논문지
• /
• 제17권9호
• /
• pp.99-106
• /
• 2017

본 연구는 진단용 검출기가 결함이 발생하는 경우 환자의 방사선 피폭과 영상의 화질에 영향을 줄 수 있다는 점에 착안하여 실험을 진행하였고 선량분석을 통해 검출기 성능을 신호 대 잡음비와 대조도 대 잡음비로 평가하였다. 선량계, 조직등가팬텀을 이용해 흡수선량과 신호 대 잡음비, 대조도 대 잡음비를 측정하였다. 실험방법은 팬텀 후면에 부착하여 나온 선량 값과 검출기 뒤에 부착한 선량 값이 일치하는지를 비교하였고 두개부 흉부 복부의 조건을 각각 75 kVp 25 mAs, 110 kVp에 8 mAs, 80 kVp에 20mAs로 설정하고 검사하였다. 그 결과 검출기의 뒤쪽에 부착한 선량값은 0.004 mGy, 0.006 mGy, 0.003 mGy로 나타났고, 팬텀 후면은 0.006 mGy, 0.016 mGy, 0.017 mGy로 차이가 있었다. 두 값을 일치시키기 위해서 조건이 증가하였고 신호 대 잡음비와 대조도 대 잡음비는 88.32, 88.10, 4.09, 1.63, 87.94, 79.97에서 93.87, 93.75, 4.91, 4.03, 92.02, 84.92로 증가하였다. 본 연구를 통해 검출기가 노후화 되는 경우 기기의 수명단축과 환자의 선량증가의 원인이 되었으며 또한 영상화질의 개선효과도 미비하다는 것을 알 수 있었다.

• Journal of Radiation Protection and Research
• /
• 제48권4호
• /
• pp.167-174
• /
• 2023

Background: A nondestructive test is commonly used to inspect the surface defects and internal structure of an object without any physical damage. X-rays generated from an electron accelerator or a tube are one of the methods used for nondestructive testing. The high penetration of X-rays through materials with low atomic numbers makes it difficult to discriminate between these materials using X-ray imaging. The interaction characteristics of neutrons with materials can supplement the limitations of X-ray imaging in material discrimination. Materials and Methods: The radiation image acquisition process for air-cargo security inspection equipment using X-rays and neutrons was simulated using a GEometry ANd Tracking (Geant4) simulation toolkit. Radiation images of phantoms composed of 13 materials were obtained, and the R-value, representing the attenuation ratio of neutrons and gamma rays in a material, was calculated from these images. Results and Discussion: The R-values were calculated from the simulated X-ray and neutron images for each phantom and compared with those obtained in the experiments. The R-values obtained from the experiments were higher than those obtained from the simulations. The difference can be due to the following two causes. The first reason is that there are various facilities or equipment in the experimental environment that scatter neutrons, unlike the simulation. The other is the difference in the neutron signal processing. In the simulation, the neutron signal is the sum of the number of neutrons entering the detector. However, in the experiment, the neutron signal was obtained by superimposing the intensities of the neutron signals. Neutron detectors also detect gamma rays, and the neutron signal cannot be clearly distinguished in the process of separating the two types of radiation. Despite these differences, the two results showed similar trends and the viability of using simulation-based radiation images, particularly in the field of security screening. With further research, the simulation-based radiation images can replace ones from experiments and be used in the related fields. Conclusion: The Korea Atomic Energy Research Institute has developed air-cargo security inspection equipment using neutrons and X-rays. Using this equipment, radiation images and R-values for various materials were obtained. The equipment was reconstructed, and the R-values were obtained for 13 materials using the Geant4 simulation toolkit. The R-values calculated by experiment and simulation show similar trends. Therefore, we confirmed the feasibility of using the simulation-based radiation image.

• 대한방사선기술학회지:방사선기술과학
• /
• 제32권3호
• /
• pp.307-312
• /
• 2009

CT 검사에서 수정체 차폐용 비스무트(bismuth)를 사용하여 수정체 선량의 감소효과를 유리선량계로 측정하여 비스무트 차폐효과 및 영상을 평가하였다. 안구 및 두부 CT 검사에서 차폐용 비스무트를 사용하여 수정체 선량의 감소와 차폐 효과를 평가하기 위해 인체모형 팬텀으로 유리선량계를 이용하여 수정체 선량을 평가하였다. 유리선량계를 이용하여 비스무트를 사용하기 전의 평균 선량은 21.54 mGy이었고, 사용 후의 선량은 10.46 mGy로 51.3%의 선량 감소효과가 있다. 차폐용 비스무트를 사용한 안구 64 MDCT 촬영에서 선량감소 효과가 있어 수정체를 포함한 안구 CT 스캔에서는 비스무트를 사용하여 검사하도록 권고한다.

• Nuclear Engineering and Technology
• /
• 제55권10호
• /
• pp.3907-3912
• /
• 2023

Radiation portal monitors (RPMs) installed at airports and harbors to prevent illicit trafficking of radioactive materials generally use large plastic scintillators. However, their energy resolution is poor and radionuclide identification is nearly unfeasible. In this study, to improve isotope identification, a RPM system based on a multi-array plastic scintillator and convolutional neural network (CNN) was evaluated by measuring the spectra of radioactive sources. A multi-array plastic scintillator comprising an assembly of 14 hexagonal scintillators was fabricated within an area of 50 × 100 cm². The energy spectra of ¹³⁷Cs, ⁶⁰Co, ²²⁶Ra, and ⁴K (KCl) were measured at speeds of 10-30 km/h, respectively, and an energy-weighted algorithm was applied. For the CNN, 700 and 300 spectral images were used as training and testing images, respectively. Compared to the conventional plastic scintillator, the multi-arrayed detector showed a high collection probability of the optical photons generated inside. A Compton maximum peak was observed for four moving radiation sources, and the CNN-based classification results showed that at least 70% was discriminated. Under the speed condition, the spectral fluctuations were higher than those under dwelling condition. However, the machine learning results demonstrated that a considerably high level of nuclide discrimination was possible under source movement conditions.

• 방사선산업학회지
• /
• 제9권2호
• /
• pp.85-90
• /
• 2015

Purpose: Time of operation has been reduced and accuracy of operation has been improved since C-arm, which offer real-time image of patient, was introduced in operation room. However, because of the contamination of patient, C-arm could not be used more appropriately. Therefore, this study is to know factors of controlling exposure dose, image quality and the exposed dose of health professional in operation room. Materials and methods: Height of Wilson frame (bed for operation) was fixed at 130 cm. Then, Model 76-2 Phantom, which was set by assembling manual of Fluke Company, was set on the bed. Head/Spine Fluoroscopy AEC mode was set for exposure condition. According to detector size of C-arm, the absorbed dose per min was measured in the 7 steps OFD (cm) from 10 cm to 40 cm (10, 15, 20, 25, 30, 35, 40 cm). In each step of OFD, the absorbed dose per min of same diameter of collimation was measured. Moreover, using Nero MAX Model 8000, exposure dose per min was measured according to 3 step of distance from detector (20 cm, 60 cm, 100 cm). Finally, resolution was measured by CDRH Disc Phantom and magnification of each OFD was measured by aluminum stick bar. Result: According to detector size of C-arm, difference of absorbed dose shows that the dose of 20 cm OFD is 1.750 times higher than the dose of 40 cm OFD. It means that the C-arm, which has smaller size of detector, shows the bigger difference of absorbed dose per min (p<0.05). In the difference of absorbed dose in the same step of OFD (from 20 cm to 40 cm), the absorbed dose of 9 inch detect or C-arm was 1.370 times higher than 12 inch' s (p<0.05). When OFD was set to 20 cm OFD, the absorbed dose of non-collimation case was approximately 0.816 times lower than the absorbed dose of collimation cases (p<0.05). When the distance was 20 cm from detector, exposed does includes first-ray and scatter-ray. When the distance was 60 cm and 100 cm from detector, exposed does includes just scatter-ray. So, there was the 2.200 times difference of absorbed does. Finally, when OFD was increased, spatial resolution was 4 to 5 step was increased. However, low contrast resolution was not relative. Moreover, there was 1.363 times difference of magnification (p<0.05). Conclusion: When C-Arm is used, avoiding contamination of patient is more important factor than reducing exposed dose of health professional in operation room. Just controlling exposure time is just way to reduce the exposed does of workers. However, in the case, non-probability influence could be occurred. Therefore, this study proved that the exposed dose will be reduced if the factors such as using small detector size of C-arm, setting OFD from 20 cm to 25 cm and non-collimating. Moreover, dose management of C-arm in the non-interesting area will be considered additionally.

• 대한방사선치료학회지
• /
• 제29권2호
• /
• pp.43-51
• /
• 2017

목 적: 유방암 환자의 방사선치료 시 엎드린 자세를 적용하면 폐와 심장에 들어가는 선량을 줄일 수 있다. 하지만 빔 방향에 포함되는 couch의 영향으로 피부선량 증가 및 심부선량이 감소한다. 따라서 본 실험에서는 air gap을 이용해서 couch로 인한 영향을 줄일 수 있는 방법을 알아보고자 하였다. 대상 및 방법: 본원에서 치료 받은 유방암 환자의 전산화단층영상을 바탕으로 3D 프린터(Builder Extreme 1000)를 이용하여 체적을 동일하게 묘사한 인체모형을 제작하였다. 제작한 인체모형을 전산화단층촬영하고 전산화치료계획시스템(Eclipse 13.6, Varian, USA)을 이용하여 6MV, Field-in-Field technique을 이용한 200 cGy/fx의 치료계획을 수립하였다. 피부선량 측정을 위해 내, 외측 4 지점(Med 1, Med 2, Lat 1, Lat 2)에서 광자극발광선량계(Optically Stimulated Luminescence Detector, OSLD)를 이용한 측정을 진행하였고, 심부선량 측정을 위해 유방의 전면과 후면의 2 지점(Anterior, Posterior)에서 FC65-G ion-chamber를 이용한 측정을 하였다. Couch와 인체모형 사이의 air gap(기준 3 cm)을 1 cm 씩 총 6 cm까지 증가시켜가며 측정하였으며 치료계획 선량을 기준으로 평가하였다. 결 과: 피부선량 측정 결과 외측 지점은 치료계획과 비교하여 ${\pm}5%$ 이내의 유사한 값을 보였다. 내측 1 지점은 air gap이 증가할수록 감소하며 3 cm 이상부터 7 % 이상 감소하였고, 내측 2 지점은 4 % 이상 감소하였다. 심부선량 측정 결과 후면 지점은 air gap 차이에 의한 선량변화가 ${\pm}1%$ 이내의 값을 보였다. 전면 지점의 선량은 air gap이 증가할수록 높아지며 3 cm 이상부터 치료계획 보다 4 % 증가한 값을 보였다. 결 론: 본 실험을 통해 couch와 인체모형 사이의 air gap을 특정 거리까지 증가시켰을 때 couch로 인한 피부선량과 심부선량의 영향이 감소함을 확인하였다. 따라서 유방암 환자에 대한 치료 전 선량평가를 진행하여 각 환자에게 최적의 air gap을 적용한다면 피부보효 효과를 높일 수 있고, 정확한 심부선량의 전달이 가능할 것으로 사료된다.

• Journal of Astronomy and Space Sciences
• /
• 제19권2호
• /
• pp.151-162
• /
• 2002

인공위성에서의 우주방사선 차폐계산을 위한 근사계산 방법으로 sectoring method를 적용하는 방법과 chord-length 분포를 이용하는 방법을 상세 계산 결과와 비교하였다. 저 궤도 위성인 우리별 1호를 대상으로 양성자의 차폐계산을 수행하였다. 이때 방사선환경은 AP-8 model을 이용하여 구한 SAA(South Atlantic Anomaly)지역으로 가정하였다. Sectoring method와 chord-length 분포를 이용하는 방법은 양성자가 물질내에서 직진한다는 기본적인 가정을 사용하므로 3차원 상세계산 결과와 비교하여 어느 정도의 오차를 갖는다. 그러나 우리별 1호를 대상으로 수행된 계산 결과에서 두 계측기 위치에서의 피폭량 예측은 2가지 근사모델이 모두 상세계산 결과와 근사하게 일치하였다.