영상유도 방사선 치료를 위한 디지털 단층영상합성법의 촬영조건 최적화에 관한 연구

윤한빈,김진성,조민국,장선영,송영재,김호경,Youn, Han-Bean,Kim, Jin-Sung,Cho, Min-Kook,Jang, Sun-Young,Song, William Y.,Kim, Ho-Kyung 한국의학물리학회 2010 의학물리 Vol.21 No.3

최근 디지털 단층영상합성법을 영상유도 방사선 치료에 활용하기 위한 연구가 활발히 시도되고 있다. 적은 수의 투사영상으로 삼차원 영상재구성이 가능하기 때문에 환자에 대한 피폭선량을 줄일 수 있으며, 환자의 움직임을 최소화할 수 있는 장점이 있기 때문이다. 그러나 단층영상의 화질이 스캔 각도(${\beta}_{scan}$) 및 사용한 투사영상의 수 등 촬영조건에 크게 의존하는 단점이 있다. 본 연구에서는 필터링 후 역투사법을 이용한 디지털 단층영상합성의 구현에 대해 자세히 논하였으며, 이에 대한 최적 촬영조건에 대해 살펴 보았다. 이를 위해 시스템 성능을 신호 대 잡음비, 잔상퍼짐함수, 연산횟수를 조합한 이득함수로 정의하였으며, 다양한 촬영조건에 대해 실험을 통해 각 지표를 구한 후 평가하였다. 평가 결과 및 분석으로부터 큰 단위 스캔 각도(${\Delta}{\beta}$)로 60도 이상의 넓은 범위에 걸쳐 스캔을 할수록 높은 화질의 단층영상을 얻을 수 있다는 결론을 얻었다. 대략적으로 시스템 성능이 $\sqrt{{\Delta}{\beta}}{\times}{\beta}^{2.5}_{scan}$에 비례하였다. 만약 각 평가지표에 명확한 가중치를 부여할 수 있다면 보다 엄밀하고 구체적인 촬영조건을 구할 수 있을 것이다. Cone-beam digital tomosynthesis (CBDT) has greatly been paid attention in the image-guided radiation therapy because of its attractive advantages such as low patient dose and less motion artifact. Image quality of tomograms is, however, dependent on the imaging conditions such as the scan angle (${\beta}_{scan}$) and the number of projection views. In this paper, we describe the principle of CBDT based on filtered-backprojection technique and investigate the optimization of imaging conditions. As a system performance, we have defined the figure-of-merit with a combination of signal difference-to-noise ratio, artifact spread function and floating-point operations which determine the computational load of image reconstruction procedures. From the measurements of disc phantom, which mimics an impulse signal and thus their analyses, it is concluded that the image quality of tomograms obtained from CBDT is improved as the scan angle is wider than 60 degrees with a larger step scan angle (${\Delta}{\beta}$). As a rule of thumb, the system performance is dependent on $\sqrt{{\Delta}{\beta}}{\times}{\beta}^{2.5}_{scan}$. If the exact weighting factors could be assigned to each image-quality metric, we would find the better quantitative imaging conditions.

Structural Similarity Index 인자를 이용한 방사선 분할 조사간 환자 체위 변화의 자동화 검출능 평가: 초기 보고

윤한빈,전호상,이자영,이주혜,남지호,박달,김원택,기용간,김동현,Youn, Hanbean,Jeon, Hosang,Lee, Jayeong,Lee, Juhye,Nam, Jiho,Park, Dahl,Kim, Wontaek,Ki, Yongkan,Kim, Donghyun 한국의학물리학회 2015 의학물리 Vol.26 No.4

현대 방사선치료는 고선명 X선 투사영상을 이용하여 환자 및 종양의 위치를 확인하는 기술이 요구되지만, 3차원 영상 촬영을 위한 피폭량 및 영상정보의 급격한 증가는 환자에게 추가적인 부담이 될 수 있다. 본 연구에서는 영상의 구조 정보를 효과적으로 추출할 수 있는 Structural similarity (SSIM) 인자를 도입하여 매일 촬영하는 환자의 2차원 X선 영상간 차이를 자동 분석하여 환자의 위치 정확성의 검증 가능성을 제시하였다. 먼저 종양을 모사하기 위하여 구형 전산 팬텀의 크기와 위치를 변화시키면서 각각의 투사 영상을 시뮬레이션하고, SSIM 인자를 통해 영상 간 차이를 검출하여 분석하였다. 또한 12일간 매일 촬영한 방사선 치료 환자의 2차원 X선 영상들 간 차이를 동일한 방법으로 검출하였다. 그 결과 산출된 팬텀 변화에 따른 SSIM 값은 0.85~1 범위로, 관심영역(ROI)을 영상 전체가 아닌 팬텀으로 한정하였을 때는 0.006~1 범위로 나타나서 ROI 적용 시 민감도가 크게 상승하는 것을 확인하였다. 또한 임상 영상의 SSIM은 0.799~0.853 범위의 값을 나타냈으며 영상 간 차이가 SSIM 분포 상에 검출되는 것을 확인하였다. 본 연구결과는 소요 시간 및 피폭 등의 우려로 매일 사용하기 어려운 3차원 영상기법 대신 간단한 2차원 영상만을 이용하여 객관적이고 정량적인 환자 위치 정확성의 자동 평가 기법을 제공할 수 있을 것으로 기대된다. The modern radiotherapy technique which delivers a large amount of dose to patients asks to confirm the positions of patients or tumors more accurately by using X-ray projection images of high-definition. However, a rapid increase in patient's exposure and image information for CT image acquisition may be additional burden on the patient. In this study, by introducing structural similarity (SSIM) index that can effectively extract the structural information of the image, we analyze the differences between daily acquired x-ray images of a patient to verify the accuracy of patient positioning. First, for simulating a moving target, the spherical computational phantoms changing the sizes and positions were created to acquire projected images. Differences between the images were automatically detected and analyzed by extracting their SSIM values. In addition, as a clinical test, differences between daily acquired x-ray images of a patient for 12 days were detected in the same way. As a result, we confirmed that the SSIM index was changed in the range of 0.85~1 (0.006~1 when a region of interest (ROI) was applied) as the sizes or positions of the phantom changed. The SSIM was more sensitive to the change of the phantom when the ROI was limited to the phantom itself. In the clinical test, the daily change of patient positions was 0.799~0.853 in SSIM values, those well described differences among images. Therefore, we expect that SSIM index can provide an objective and quantitative technique to verify the patient position using simple x-ray images, instead of time and cost intensive three-dimensional x-ray images.

3D 프린팅 비압박 유방 팬텀 제작을 위한 복셀 기반 수치 모델에 관한 연구

윤한빈,백철하,전호상,김진성,남지호,이자영,이주혜,박달,김원택,기용간,김동현,원종훈,김호경,Youn, Hanbean,Baek, Cheol Ha,Jeon, Hosang,Kim, Jinsung,Nam, Jiho,Lee, Jayoung,Lee, Juhye,Park, Dahl,Kim, Wontaek,Ki, Yongkan,Kim, Donghyun,Won, Jong 대한의용생체공학회 2017 의공학회지 Vol.38 No.3

Physical breast phantoms would be useful for the development of a dedicated breast computed tomography (BCT) system and its optimization. While the conventional breast phantoms are available in compressed forms, which are appropriate for the mammography and digital tomosynthesis, however, the BCT requires phantoms in uncompressed forms. Although simple cylindrical plastic phantoms can be used for the development of the BCT system, they will not replace the roles of uncompressed phantoms describing breast anatomies for a better study of the BCT. In this study, we have designed a numerical voxel breast phantom accounting for the random nature of breast anatomies and applied it to the 3D printer to fabricate the uncompressed anthropomorphic breast phantom. The numerical voxel phantom mainly consists of the external skin and internal anatomies, including the ductal networks, the glandular tissues, the Cooper's ligaments, and the adipose tissues. The voxel phantom is then converted into a surface data in the STL file format by using the marching cube algorithm. Using the STL file, we obtain the skin and the glandular tissue from the 3D printer, and then assemble them. The uncompressed breast phantom is completed by filling the remaining space with oil, which mimics the adipose tissues. Since the breast phantom developed in this study is completely software-generated, we can create readily anthropomorphic phantoms accounting for diverse human breast anatomies.

Characterization of On-site Digital Mammography Systems: Direct Versus Indirect Conversion Detectors

윤한빈,한종철,윤성만,감수화,조승룡,김호경 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.12

We investigated the performances of two digital mammography systems. The systems use a cesium-iodide (CsI) scintillator and an amorphous selenium (a-Se) photoconductor for X-ray detection and are installed in the same hospital. As physical metrics, we measured the modulationtransfer function (MTF), the noise-power spectrum (NPS), and the detective quantum efficiency (DQE). In addition, we analyzed the contrast-detail performances of the two systems by using a commercial contrast-detail phantom. The CsI-based indirect conversion detector provided better MTF and DQE performances than the a-Se-based direct conversion detector whereas the former provided a poorer NPS performance than the latter. These results are explained by the fact that the CsI-based detector used an MTF restoration preprocessing algorithm. The a-Se-based detector showed better contrast-detail performance than the CsI-based detector. We believe that the highfrequency noise characteristic of a detector is more responsible for the visibility of small details than its spatial-resolution performance.

컴퓨터 원용 결함진단을 위한 그래픽 솔루션 개발에 관한 연구

윤한빈(Hanbean Yoon),윤승만(Seungman Yun),한종철(Jong Chul Han),조민국(Min Kook Cho),임창휘(Chang Hwy Lim),허성근(Sung Kyn Heo),손철순(Cheol-Soon Shon),김성식(Seong-Sik Kim),이석희(Seok-Hee Lee),이석(Suk Lee),김호경(Hokoung Kim) 한국비파괴검사학회 2009 한국비파괴검사학회지 Vol.29 No.1

역공학의 한 방법으로 엑스선 전산 단층촬영 장치에서 획득한 삼차원 데이터를 CAD(computeraided design) 데이터로 변환하여 쾌속조형 모델을 제작할 수 있고, 또한 삼차원 가시화를 통해 피검사체의 오차를 확인하고 분석할 수 있는 알고리즘들에 대한 연구를 수행하였다. 연구 결과를 바탕으로 GUI(graphical user interface) 기반의 소프트웨어를 개발하였다. 개발한 소프트웨어의 검증을 위하여 산업 및 의료용 샘플들에 대한 전산 단층촬영 스캐닝을 수행하고 CAD 데이터 변환 및 컴퓨터 원용 결함진단 시뮬레이션을 수행하였다. 이를 통해 컴퓨터 원용 결함진단의 산업 및 의료분야 적용 가능성을 확인하였다. We have developed software for converting the volumetric voxel data obtained from X-ray computed tomography(CT) into computer-aided design(CAD) data. The developed software can used for non-destructive testing and evaluation, reverse engineering, and rapid prototyping, etc. The main algorithms employed in the software are image reconstruction, volume rendering, segmentation, and mesh data generation. The feasibility of the developed software is demonstrated with the CT data of human maxilla and mandible bones.

Finite Element Analysis of the Effects of Pixel Geometry on Electrical Properties in Semiconductor Pixel Detectors

박하령,윤한빈,한종철,감수화,김호경 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.5

The development of photon-counting pixel detectors for spectral x-ray imaging is in its prime. The optimization of pixel geometry is crucial for obtaining a reliable spectral response in each pixel element with the least distortion due to fundamental x-ray interactions and electrical properties. We investigated the fundamental electrical properties in semiconductor pixel detectors with respect to normalized pixel geometries: the aspect ratio (the length ratio between pixel pitch and detector thickness) and the fill factor (the area ratio between the pixel electrode and pixel extent). For various geometries, we performed three-dimensional field simulations using a commercial finite element analysis code, and obtained the potential and field distributions. Based on weighting potential distributions, we calculated the net charge buildup for various interaction positions within the boundary of pixel, where a single electron-hole pair starts to drift, assuming no charge trapping and diffusion. For upper limit performance, a small aspect-ratio and fill-factor design would be preferable for fast and reliable signal measurements. The results and methodology from this study can offer insight into the optimal design of pixel geometries in photon-counting pixel detectors.

컴퓨터 단층영상에서 사이노그램 정규화를 이용한 금속 영상왜곡 저감 방법의 이론적 고찰

전호상,윤한빈,남지호,김호경,Jeon, Hosang,Youn, Hanbean,Nam, Jiho,Kim, Ho Kyung 한국의학물리학회 2013 의학물리 Vol.24 No.4

금속 인공물을 포함한 인체 단층영상의 경우 금속 영상왜곡으로 인한 화질의 저하가 매우 심각하다. 금속 영상왜곡 저감을 위한 많은 방법 중 사이노그램 정규화를 통해 평탄한 사이노그램을 제공하여 금속 궤적을 쉽게 찾고, 단순 선형 보간으로 금속물을 대체하는 두께 및 배경 정규화 방법이 최근 소개되었다. 본 연구에서는 두 방법의 이론적 배경을 개발하였으며, 시뮬레이션을 통해 금속 인공 물질의 크기 및 개수에 따른 두 방법의 보정 결과를 비교하였다. 개발한 이론에 의하면 배경 정규화 방법이 두께 정규화 방법에 비해 피검사체 배경 구성 물질의 개수 및 종류에 상관없이 거의 평탄한 사이노그램을 제공하였으며, 시뮬레이션을 통해 이를 증명하였다. 금속 인공 물질의 다양한 크기 및 개수에 대한 두 방법의 보정 결과 역시 배경 정규화 방법이 두께 정규화 방법에 비해 훨씬 나은 보정 결과를 보여 주었다. 배경 정규화 방법은 영상분할 과정을 요구하는데 본 연구에서는 이 과정을 생략하더라도 비록 영상왜곡 잔상이 미약하게 나타나긴 하지만, 두께 정규화 방법에 비해 훨씬 나은 보정 결과를 제공함을 확인하였다. 영상분할 과정을 생략한 배경 정규화 방법은 매우 간단하며 단순 선형 보간으로도 금속 궤적에 의해 손실된 데이터의 기술이 충분하고, 또한 사용자의 개입이 없는 알고리즘화가 가능하기 때문에 기존 컴퓨터단층영상 시스템에 쉽게 탑재되어 활용될 수 있을 것으로 기대된다. Image quality of computed tomography (CT) is very vulnerable to metal artifacts. Recently, the thickness and background normalization techniques have been introduced. Since they provide flat sinograms, it is easy to determine metal traces and a simple linear interpolation would be enough to describe the missing data in sinograms. In this study, we have developed a theory describing two normalization methods and compared two methods with respect to various sizes and numbers of metal inserts by using simple numerical simulations. The developed theory showed that the background normalization provide flatter sinograms than the thickness normalization, which was validated with the simulation results. Numerical simulation results with respect to various sizes and numbers of metal inserts showed that the background normalization was better than the thickness normalization for metal artifact corrections. Although the residual artifacts still existed, we have showed that the background normalization without the segmentation procedure was better than the thickness normalization for metal artifact corrections. Since the background normalization without the segmentation procedure is simple and it does not require any users' intervention, it can be readily installed in conventional CT systems.

Enhancement in the kV Portal Image Contrast Using Depth Normalization for Accurate Patient Localization

전호상,윤한빈,남지호,이자영,이주혜,박달,김원택,기용간,김동현,김호경 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.4

The X-ray imaging modality has played an important role in the daily verification of a patient's position for accurate radiation treatment (RT), especially in modern RT techniques that require highly precise patient localization. Although cone-beam computer tomography (CBCT) has already been introduced to the RT field, two-dimensional (2D) X-ray portal imagers have been more widely used than CBCT for the daily check of patient localization owing to the lower patient exposure and time consumption. However, the 2D imager practically provide a lower bone-tissue contrast than CBCT. Thus, we propose a method that enhances the image contrast of daily acquired 2D images by using just one CBCT scan during an entire RT course. This method operates on the basis of the depth normalization (DN) technique and requires no artificial data manipulation such as image post-processing filters. We implemented the algorithm for the portal images of a cylindrical phantom and three patients. From DN results, the image contrast for the phantom and the patients increased by factors of 26.3 and 13.4 on average, and their contrast-to-noise ratios were maintained at differences of 8.6% and 7.7% on average, respectively. Moreover, the DN method provided a stronger contrast enhancement at lower doses that could suppress the imaging exposure and thus improve the patient's safety. Therefore, the verification of RT patient localization is expected to be performed more eciently and accurately by using the DN method.

암모니아 급성노출에 따른 대왕범바리(Epinephelus fuscoguttatus ♀×E. lanceolatus ♂)의 혈액성상 및 혈장성분의 변화

김광민,이희진,윤한빈,조재황,김석렬,이경미,김준환,Kim, Kwang-Min,Lee, Hee-Jin,Yun, Han Bin,Cho, Jae-Hwang,Kim, Seok-Ryel,Lee, Kyung Mi,Kim, Jun-Hwan 한국환경생물학회 2020 환경생물 : 환경생물학회지 Vol.38 No.1

Hybrid grouper(Epinephelus fuscoguttatus ♀×E. lanceolatus ♂) (mean weight 25.7±3.5g, mean length 11.2±0.9cm) were exposed to different ammonia concentrations of 0, 5, 10, 20, and 40mg L^-1 for 96 hours. The hematological hematocrit and hemoglobin parameters of the hybrid grouper were significantly decreased by 20 mg L^-1 ammonia exposure. In the organic plasma components, calcium was significantly decreased, whereas there was no change in magnesium. In the organic plasma components, the glucose and cholesterol values of the hybrid grouper were significantly increased by ammonia exposure. In the enzymatic plasma components, the ALP(Alkaline phosphatase) value of the hybrid grouper was also significantly increased by ammonia exposure. The results of this study demonstrate that acute ammonia exposure to hybrid grouper induced changes in hematological parameters and plasma components. Therefore, acute ammonia exposure over 20 mg L^-1 appears to be toxic to hybrid grouper and the results can be used as a major indicator in breeding hybrid grouper. 본 실험에서 암모니아 급성 노출은 대왕범바리의 혈액학적 성상 및 혈장 성분에 유의적 변화를 나타내었다. 본 실험의 결과 20mg L^-1 이상의 급성 암모니아 노출은 대왕범바리의 혈액학적 성상 및 혈장 성분에 영향을 주어 생리적 변화를 일으키며, 40mg L^-1의 급성 암모니아 농도는 대량 폐사를 유발할 수 있음을 나타낸다. 향후 대왕범바리 바이오플락 양식기술 적용을 위한 양식연구에 이러한 결과를 지표로 활용할 수 있을 것이다.

마이크로 단층촬영시스템에서의 기하학적 보정에 관한 연구

장선영,김호경,윤한빈,윤승만,조옥라,송영재,김성식 한국정밀공학회 2011 한국정밀공학회 학술발표대회 논문집 Vol.2011 No.6월