전자상자성공명분광계의 개발 및 치아 누적 방사선량의 체내 측정을 위한 정확도 개선

학위논문 (박사)-- 서울대학교 대학원 : 융합과학기술대학원 융합과학부, 2019. 2. 예성준.A homebuilt EPR spectrometer has been developed as an in-vivo radiation dosimeter in situ. The EPR spectrometer consisted of magnets, field driving circuits, a bridge circuit, a surface-coil-type resonator, and operation software programmed in LabVIEW. Using the developed system, radiation doses to extracted tooth were estimated in terms of the standard error of inverse prediction (SEIP). Then, we also conducted simulations and experiments for the evaluation of feasibility for use as an in-vivo dosimeter. For understanding of inter-tooth difference in EPR intensity, we generated the simulation set. First, the structures of tooth were separately investigated for enamel, dentin and pulp for each tooth. Second, we investigated the variations of EPR signal with the tooth dimensions. Finally, we generated the simulation set with the probable setup such as angle and distance between tooth and resonator. Then, simulated RIS (radiation-induced signal) amplitudes (sRIS) were calculated for each simulation set. For confirmation, we performed the measurements to acquire mRIS (measured RIS). Then, we calculated R2 value to find the relation among RIS and tooth dimensions using linear regression fitting. We applied the geometric correction based on labial enamel area for improvement of dose estimation. The SEIP was calculated based on mRIS. Three head and neck (HN) volumetric-modulated arc therapy (VMAT) plans were selected. The verification plans were generated using the CT images of the head phantom based on the original HN 6 MV VMAT plans using treatment planning system (TPS). Radiation treatment plans were delivered to head phantom. Then, we compared the dose between TPS and in- vivo EPR. The integrated magnet system was customized product manufactured by Resonance Research Inc. (Billerica, MA). The gap between magnets was 17 cm which was proper size for insertion of human head. The maximum range of sweep field was 38 mT to 43 mT. The fabricated resonator showed a resonance peak was observed at 1.15 GHz. The variations in sRIS with angle were less than ±16% and ±6% respect to y-axis and z-axis in range of ±6°. The sRIS for incisors was rapidly decreased to 20% with distance between the coil and tooth at 0.3 mm. The R2 value was higher than 0.8 between sRIS and mRIS with tooth dimensions such as total enamel volume, labial enamel volume and labial enamel area. The EPR intensity of RIS for all measured tooth samples was linearly increased with increasing doses, of which the slopes varied over tooth samples. With labial enamel area adjustment, relative standard error of slope for the calibration curves were reduced to 2.9% from 7.1% of non-adjusted calibration curves. The estimated dose using in-vivo EPR in dose range of TPS predicted except T2 and T3 of plan 1 among used tooth for all plans in a beam delivery. The estimated dose using in-vivo EPR in dose range of TPS predicted after beam delivery five times more. The EPR spectrometer for in-vivo dosimetry was successfully developed for human intact tooth for dose estimation instantly in 5 minutes. We also found an evidence of geometry of tooth including enamel volume and area. The developed system was broadened its applications to a routine in-vivo dosimetry for radiation therapy.현장에서 측정가능한 체내측정용(in-vivo) 방사선 선량추정(dose estimation)을 위한 전자상자성공명(EPR)분광계를 개발했다. EPR분광계는 자석(magnet), 자기장 구동회로(field driving circuit), 브릿지 회로(bridge circuit), 표면형 코일 공진기(surface-coil-type resonator), 그리고 LabVIEW로 구현한 제어 프로그램 등으로 구성됐다. 개발된 장비를 활용하여 추출한 치아의 방사선량을 반대예측표준오차(SEIP)를 추정했다. 그 다음, 체내 선량측정용 장비로서 활용가능성을 전산모사와 실험을 통해 평가했다. EPR신호의 치아간(inter-tooth) 차이를 이해하기 위하여, ANSYS HFSS로 전산모사 세트들을 생성했다. 첫째로, 치아의 구조물인 법랑질(enamel), 상아질(dentin) 그리고 치수(pulp)를 분리하여 분석했다. 둘째로, EPR신호의 치아의 치수(tooth dimension)별 변화를 조사했다. 마지막으로, 공진기와 치아간 간격과 각도 등의 여러 측정상황 별 전산모사 세트들을 생성했다. 그 다음, 전산모사 RIS(Radiation-induced signal) 크기 (sRIS)를 각 전산모사 세트 별로 계산했다. 이 관계를 검증하기 위해 측정 RIS (mRIS)를 수집했다. 그 다음, RIS와 치아의 치수 별 관계를 이해하기 위하여 선형회귀분석으로 R 2값을 계산했다. 선량추정의 정확도를 개선하기 위해서 입술방향 치아면적(labial enamel area)을 활용해 기하학적 교정을 수행했다. SEIP는 mRIS를 바탕으로 계산했다. 3명의 두경부(HN) 체적변조방사선치료(VMAT) 치료계획을 선택하여, 검증을 위한 치료계획(verification plan)들은 두부팬톰(head phantom)의 CT영상을 바탕으로 6MV VMAT 치료계획을 치료계획소프트웨어(TPS)로 생성했다. 이 방사선치료계획을 활용하여 두부팬톰에 방사선을 조사했다. 그 다음 TPS로 계산한 방사선량과 in-vivo EPR로 측정한 선량을 비교했다. 자기장발생부(integrated magnet system)은 Resonance Research사에서 주문 제작했다. 자석 사이의 간격은 17 cm로 인체의 두부가 충분히 들어갈 수 있도록 설계됐다. 자기장 세기는 38 mT부터 43 mT까지 스윕이 가능 하도록 설계했다. 제작된 공진기는 1.15 GHz 근처에서 공진점을 확인했다. sRIS크기변화는 ± 6˚각도 범위에서 y축에 대해서 ± 16% z축에 대해서 ± 6 이내였다. 치아와 코일간 거리가 0.3 mm 일 때, sRIS는 0 mm 대비 약 20% 감소했다. sRIS 및 mRIS과 법랑질의 체적, 법랑질의 입술방향 체적볼륨 그리고 법랑질의 입술방향 면적 등의 R 2값은 0.8 이상으로 높은 선형성을 보였다. 누적방사선량이 증가할수록 RIS도 선형적으로 증가함을 확인했고, 선량커브들의 기울기의 상대표준오차(RSE)는 치아 별 법랑질면적으로 교정 후 7.1%에서 2.9%로 개선됐다. 팬톰조사 결과에서 VMAT치료계획을 한 번 전달한 후의 Plan 1의 T2와 T3을 제외하고 선량추정결과가 모두 TPS로 계산한 방사선량의 범위 내에 들어왔다. 인간 치아를 대상으로 하는 체내 측정용 EPR분광계를 성공적으로 개발했으며, 선량추정결과는 측정 시작 후 5분 뒤에 0.5 Gy 선량추정오차로 확인 가능하다. 법랑질의 체적 및 면적을 포함한 치아의 기하학적인 인자들과 RIS간 관계의 증거를 확인했다. 또, 방사선 치료 시 체내 방사선량 측정장비로서 TPS의 선량결과와 개발한 EPR분광계의 방사선치료 시 체내측정용으로 적용범위를 확장했다.Chapter 1. Introduction . 1 1.1. Basics of Electron Paramagnetic Resonance 1 1.1.1. The Principle of EPR Spectroscopy . 1 1.1.1.1. g-factor . 5 1.2. Basics of Contiuous Wave EPR Spectrometer 9 Chapter II. The Development of in-vivo EPR Spectrometer . 13 2.1. Introduction 13 2.2. Methods and Materials . 15 2.2.1. Optimum Frequency of EPR Spectrometer 15 2.2.2. Configuration of EPR Spectrometer. 18 2.2.2.1. Integrated Maget System 20 2.2.2.1.1 Permanent Magnet 20 2.2.2.1.2 Sweep Magnetic Field Circuit 22 2.2.2.1.3 Modulation Magnetic Field Circuit 24 2.2.2.2. Surface Coil Type Resonator 32 2.2.2.3. Bridge and Additional Devices. 37 2.3. Results 46 2.3.1. Development of EPR spectrometer System 46 2.3.1.1. Integrated Maget System 46 2.3.1.1.1 Permanent Magnet 46 2.3.1.1.2 Sweep Magnetic Field Circuit 49 2.3.1.1.3 Modulation Magnetic Field Circuit 52 2.3.1.2. Surface Coil Type Resonator 56 2.3.1.3. Bridge and Additional Devices. 59 2.4. Discussion 61 2.5. Conclusions 62 Chapter III. The Application for in-vivo Dosimeter 63 3.1. Introduction 63 3.2. Methods and Materials . 65 3.2.1. Affecting Factors of Variation for EPR Intensity of Tooth . 65 3.2.1.1. Calculation of Simulated EPR Signal for Tooth Model 65 3.2.1.1.1 microCT-scanned Tooth Models. 65 3.2.1.1.2 Simulation Settings. 70 3.2.1.2. Goemetry of Tooth 72 3.2.1.2.1 Dimensions of Tooth Enamel 72 3.2.1.3. Setup Variations 73 3.2.1.3.1 Angle of Tooth and Detection Coil. 73 3.2.1.3.2 Distance of Tooth and Detection Coil. 75 3.2.1.4. Impacts of Structures for EPR Intensity . 77 3.2.1.5. Other Consideration of Affecting Parameters for EPR Intensity 81 3.2.1.5.1 Role of Tooth Restorations. 81 3.2.1.5.2 Sunlight and Ultraviolet 86 3.2.1.5.3 Whitening Treatment for Tooth 87 3.2.2. Evaluation of Dose Estimation Performance 89 3.2.2.1. Measurement of EPR Spectra of Tooth. 89 3.2.2.1.1 Reference Sasmple Preparation 89 3.2.2.1.2 Tooth Sasmple Preparation . 90 3.2.2.1.3 Beam Irradiation and Measurement of EPR Spectra 92 3.2.2.2. Inverse Prediction for Dose Estimation 95 3.2.3. Evaluation as in-vivo Dosimeter in Radiation Therapy 97 3.2.3.1. EPR Curve Calibration of 6 MV Photon Beam 97 3.2.3.2. OSLD Calibration. 99 3.2.3.3. Tooth Model for Head Phantom . 101 3.2.3.4. Phantom Fabrication and CT Image Acquistion . 102 3.2.3.5. Radiation Delivery with Head Phantom . 104 3.2.3.6. Measurement of EPR Signal of Tooth Model. 106 3.3. Results 108 3.3.1. Affecting Factors of Variation for EPR Intensity of Tooth . 108 3.3.1.1. Calculation of Simulated EPR Signal for Tooth Model 108 3.3.1.2. Geometry of the Tooth. 110 3.3.1.2.1 Dimensions of Tooth Enamel. 110 3.3.1.3. Setup Variations. 116 3.3.1.3.1 Angle of Tooth and Detection Coil 116 3.3.1.3.2 Distance of Tooth and Detection Coil 119 3.3.1.4. Impacts of Structures for EPR Intensity . 121 3.3.2. Evaluation of Dose Estimation Performance 125 3.3.2.1. Measurement of EPR Spectra of Tooth. 125 3.3.2.1.1 The EPR Response and Linearity . 125 3.3.2.1.2 The Calibration Curve 127 3.3.2.1.3 The Temporal Stability . 129 3.3.2.2. Inverse Prediction for Dose Estimation 131 3.3.3. Evaluation of as in-vivo Dosimeter in Radiation Therapy 133 3.4. Discussion 146 3.5. Conclusions 150 Discussion 151 Conclusions and Future work. 154 References 155 List of abbreviations. 161 Abstract (in Korean). 162Docto

Development of beamforming technique and its application to biomedical imaging

Doctor본 논문에서는 빔포밍 방법을 제안하고, 이를 의료 영상 분야에 적용한다. 더불어 이를 시스템상에 구현하고, 그래픽 프로세서를 활용한 병렬화를 통하여 계산 속도 감소 및 실제 상용화 가능 여부를 판단한다. 현재 다양한 형태의 빔포밍 방법이 존재하는데, 본 논문에서는 적응 빔포밍 방법과 비선형 빔포밍 방법에 대해 각각의 새로운 형태의 빔포밍 방법을 제안하고 이를 각각 초음파 의료 영상 및 광음향 의료 영상에 적용한다. 우선, 적응빔포밍 방법의 경우 성능은 그대로 유지하되, 기존 대비 계산량을 획기적으로 줄이는 방법을 제안하고 이를 초음파 의료 영상에 적용한다. 기존의 적응 빔포밍 방법은 적응 가중치를 계산하기 위해, 공분산 행렬 계산 및 이의 역행렬 계산을 수행해야 되는데, 이는 프로세서의 높은 수준의 연산 능력을 요구하게 되고 실시간 초음파 영상을 제공하는데 있어 걸림돌이 되었다. 본 논문에서는 QR 분해를 기반으로 한 직교화 알고리즘을 적용하여, 공분산 행렬의 계산 및 그것의 역행렬을 계산하지 않고, 기존의 적응 빔포밍 방법과 동일한 결과를 도출하는 알고리즘을 제안하였다. 이를 통해 기존 대비 계산량을 획기적으로 줄이게 되어, 실제 상용화를 위해 한발짝 더 다가가는 결과를 도출했다. 시뮬레이션 및 실제 의료 초음파 데이터를 이용해 본 알고리즘의 효용성을 입증한다. 비선형 빔포밍 방법의 경우, 시간지연곱합 빔포밍을 변경하여 광음향 분야에 적용한다. 광음향 현미경는 광음향효과를 활용한 대표적 광음향 영상 장비로써, 초점화된 초음파 트랜스듀서를 사용하여, 높은 수준의 해상도를 갖는 영상을 획득 가능케 한다. 하지만, 이러한 성능은 초점화된 영역에 국한되고, 비초점화 영역에서는 영상의 질이 급격히 떨어지게 된다. 이러한 문제를 해결하기 위해 기존에 합성 개구 초점 방법을 기반한 알고리즘을 제안하였는데, 이는 비 초점화 영역에서 영상의 질을 회복하는 결과를 도출했었다. 본 논문에서는 시간지연곱합 빔포밍 기반 합성개구초점 알고리즘을 제안하여, 기존보다 보다 향상된 성능을 보여준다. 탄소 나노 튜브를 활용한 실험 및 실제 쥐의 배와 다리 영상을 획득하여 결과를 비교함으로써 본 방법의 유효성을 입증한다. 마지막으로, 앞서 제안한 방법을 시스템상에 구현함으로써 실제 구현이 가능한지 여부를 판단한다. 적응 빔포밍 방법 및 시간지연곱합 기반 비선형 빔포밍 방법의 경우 모두 많은 연산량을 요구하여, 실제 실시간 영상 장치를 구성하는데 있어 제약이 존재하는데, 본 논문에서는 그래픽 프로세서를 활용한 병렬화를 통해 기존 대비 연산 시간을 획기적으로 줄이도록 한다. 병렬화 이전과 병렬화 이후 연산 속도를 비교함으로써 병렬화를 통한 최적화 여부를 입증한다.In this thesis, we present beamforming algorithms and their application to biomedical imaging. First, we propose a computationally efficient adaptive beamformer, i.e., a MV beamformer, based on QR decomposition and show its validity for ultrasound (US) imaging. Typically, the MV beamformer shows significantly improved resolution and interference suppression capability over the DAS beamformer, but its improvements comes at the expense of increased computational cost. Computing the spatial covariance matrix and its inverse requires large computations, which limits the use of the MV beamformer in practice. Our proposed method reduce the computational complexity, thereby taking one step closer to practical use. Second, we propose the improved DMAS beamformer and deal with the critical problem of the acoustic-resolution photoacoustic microscopy (AR-PAM). AR-PAM uses a spherically focused single element US transducer with a high N.A and frequency, which enables us to obtain high-quality photoacoustic (PA) images. However, it is limited to the focal region so the image quality in the off-focus region is significantly degraded. Using DMAS beamforming algorithm with synthetic aperture focusing technique, we obtain improve lateral resolution in off-focus region, thereby achieving the extension of the imaging focal region. Finally, we implement the proposed beamforming algorithms for the parallel computing by using a graphical processing unit (GPU). Recently, in order to handle large amounts of data, the parallel computing based on the GPU have been actively studied in various areas. The GPU consists of many streaming processors (SP) which enable parallel computing, whereas a central processing unit (CPU) has four SP at most. In addition, users can easily implement algorithms by using parallel computing platform and an application programming interfaces (API) such as CUDA (Compute Unified Device Architecture) and OpenCL (Open Computing Language). For showing potential of our algorithms for parallel computing, we compare the processing times with CPU-based serial implementation on the frameworks of MATLAB and C, respectively

신뢰성 평가를 위한 가속 열화 시험의 설계

학위논문(박사) - 한국과학기술원 : 산업공학과, 1998.2, [ 127 p. ]Accelereted degradation tests (ADTs) are widely used in many context for the reliability assessment of products. In this thesis, we develop optimal ADT plans under the assumptions of destructive testing and the simple constant rate relationship between the degradation of product performance and time. Specifically, we determine the stress levels, the proportion of test units allocated to each stress level, and the measurement times such that the asymptotic variance of the maximum likelihood estimator of the qth quantile of the lifetime distribution at the use condition is minimized. The optimization problem is formulated as a constrained nonlinear program, and exact optimal solutions are obtained for various cases. Also, the developed optimal ADT plans are compared to the corresponding optimal accelerated life test (ALT) plans in terms of the asymptotic efficiency in estimating the qth quantile and of the robustness to the mis-specifications of failure probabilities. Computational results show that the ADT provides a more precise estimator than the ALT, especially when the failure probabilities are small. As long as the robustness of a test plan to the departures of the guessed failure probabilities from their true values is concerned, neither plan completely dominates the other. Finally, we develop reliability acceptance sampling plans (RASPs) based on the ADT such that the producer and the consumer risks are satisfied.한국과학기술원 : 산업공학과

디스터번스 옵져버를 이용한 오버헤드 크레인 시스템의 제어

2

The influence of the media report's perception of supernatural phenomena.

학위논문(석사) - 한국과학기술원 : 과학저널리즘대학원프로그램, 2013.2, [ vii, 101 p. ]Pyochug Bi (3.8m), established by King Young-Jo of Joseon Dynasty in 1742, is located in the midst of Hongje Temple in Milyang, Gyeongsangnamdo to commemorate the feats and loyalty of Samyeong Daesa (great master). The monument first started perspiring a week before Gabo Reform on July 22nd 1894 after 152 years of its establishment, and 63 cases of perspiration have been reported ever since. The quantity of perspiration is tremendous. The nearby locals also call it Hanchul Bi (Sweating Stele). It is reported that it has perspired before or after good or bad national events, some of which amounted to 131.5L. The residents interpret - and believe that - as Master Samyeong’s perspiration through his supernatural powers out of his worries about the country and safety of its people. The media have also reported so over several decades. However, there still remains a question. Is the perspiration a natural phenomenon? Or else, as claimed by the residents, is it a supernatural phenomenon through Samyeong’s supernatural power? Also, it is also unanswered why on earth it always perspires around the time of domestically significant events. In Chapter 1, we present a problem and the purpose of the study, as well as its extent and methods.한국과학기술원 : 과학저널리즘대학원프로그램