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Title Page

Abstract

Contents

CHAPTER 1. INTRODUCTION 21

1.1. Mechanical Collimation Imaging(Coded aperture imaging) 22

1.2. Electronic Collimation Imaging(Compton imaging) 23

1.3. The Combination of Mechanical and Electronic Collimation Imaging 25

1.4. Objectives of This study 26

CHAPTER 2. MONTE CARLO SIMULATION AND PERFORMANCE CONSIDERATIONS FOR ACTIVE COLLIMATION DETECTION SYSTEM 28

2.1. Evaluation of dual gamma-ray imager with active collimator using various types of scintillators 28

2.1.1. Mechanical collimation 29

2.1.2. Electronic collimation 32

2.2. Simulation modeling and validation 36

2.3. Receiver operating characteristic(ROC curve) 43

2.4. Intrinsic efficiency and Resolution-variance curve(RV curve) 44

CHAPTER 3. ACTIVE COLLIMATION HARDWARE SYSTEM 45

3.1. Mechanical structure of active collimation detection system 45

3.2. Detector Characterization 47

3.2.1. Timing resolution 47

3.2.2. Energy resolution 48

3.3. Front end circuits 49

CHAPTER 4. EXPERIMENTAL RESULTS AND ANALYSIS 55

4.1. Reconstructed images, RMS ratios, and Resolution-variance curve 55

4.2. Evaluation for Resolution-variance curves(ROC curves) 62

4.3. Evaluation for Two point sources 66

CHAPTER 5. ADVANCED ACTIVE COLLIMATION SYSTEM(A CUBIC GAMMA CAMERA) 69

CHAPTER 6. SUMMARY, CONCLUSIONS AND FUTURE WORK 76

6.1. Summary 76

6.2. Conclusions 77

6.3. Future work 78

Reference 79

APPENDICES 20

APPENDIX A. COMPACT HYBRID GAMMA CAMERA WITH A CODED APERTURE FOR INVESTIGATION OF NUCLEAR MATERIALS 83

APPENDIX B. MULTIPLE-SCATTERING COMPTON CAMERAAS A PHOTON-TRACKING IMAGER FOR 6-MV PHOTON THERAPY 93

B.1. Geometrical, material of detector optimization and uncertainty factors 93

B.2. Monitoring dose distribution of therapeutic photons on voxel human phantom(KTMAN-2 PHANTOM) 99

APPENDIX C. MULTIPLE-SCATTERING COMPTON CAMERA WITH NEUTRON ACTIVATION FOR MATERIAL INSPECTION 104

List of Tables

TABLE 2.1. EFFECTIVE COUNTS OF PHOTOELECTRIC EVENT 42

TABLE 2.2. EFFECTIVE COUNTS OF COMPTON SCATTERING EVENT 42

TABLE 3.1. MEAN ENERGY RESOLUTION OF THE SINGLE DETECTORS. 48

TABLE 3.2. RATIO OF ANODE OUTPUT OF THE FIRST AND SECOND DETECTOR AFTER CORRECTION. 50

TABLE 4.1. PEAK OF SOURCE TO RMS OF BACKGROUND RATIO IN IMAGE(5×3) 56

TABLE 4.2. PEAK OF SOURCE TO RMS OF BACKGROUND RATIO IN IMAGE(7×5) 61

TABLE 4.3. COMPUTATION TIMES FOR IMAGE RECONSTRUCTION WITH 100 ITERATIONS 61

TABLE 5.1. PEAK OF SOURCE TO RMS OF BACKGROUND IN THE IMAGE 74

TABLE 5.2. COMPARISON OF DETECTION EFFICIENCY PERFORMANCE 75

TABLE A.1. PEAK OF THE SOURCE TO THE RMS OF THE BACKGROUND IN IMAGER 88

TABLE A.2. PERFORMANCE OF COMPACT HYBRID GAMMA CAMERA USING POINT SOURCES WITH VARIOUS RADIATION ENERGIES. 89

TABLE A.3. COMPARISON OF THE PERFORMANCE FOR THE TWO DETECTION SYSTEMS 92

TABLE B.1. PROPERTIES OF THE DETECTORS 93

TABLE B.2. COMPUTATlON TIMES FOR COMPTON IMAGES RECONSTRUCTION WITH 20 ITERATIONS AND DETECTION EFFICIENCIES. 103

TABLE C.1. NUCLEAR REACTIONS AND CHARACTERISTIC GAMMA-RAYS FROM THE REACTION. 104

TABLE C.2. DETECTION EFFICIENCIES AND MAXIMUM TO RMS OF BACKGROUND VALUE IN RECONSTRUCTED IMAGE. 105

List of Figures

Fig. 1.1. Basic concept of coded aperture imaging. 22

Fig. 1.2. Schematic diagram of Compton imaging. 24

Fig. 1.3. Schematic diagram of the conventional dual modality gamma-ray imaging system. 25

Fig. 1.4. Operation of the active collimation γ-ray imager for low and high energy radiation. 27

Fig. 2.1. Cross-sectional view of simulation geometries 28

Fig. 2.2. FWHM vs. incident radiation energy for various active collimators in mechanical collimation 29

Fig. 2.3. Peak counts vs. incident radiation energy for various active collimators in mechanical collimation 30

Fig. 2.4. Relative standard deviation vs. incident radiation energy for various active collimators in mechanical... 31

Fig. 2.5. FWHM vs. incident radiation energy for various active collimators in electronic collimation 33

Fig. 2.6. Peak counts vs. incident radiation energy for various active collimators in electronic collimation 34

Fig. 2.7. Relative standard deviation vs. incident radiation energy for various active collimators in electronic... 35

Fig. 2.8. Schematic of the active collimation(URA) system for simulation. 36

Fig. 2.9. Reconstruction images using a 5×3 URA array and MLEM method for a 122-keV point source... 36

Fig. 2.10. Reconstructed images using a 5×3 URA array and MLEM method for a 356-keV point source... 37

Fig. 2.11. Reconstructed images using a 5×3 URA array and MLEM method for a 662-keV point source... 37

Fig. 2.12. Reconstruction images using a 5×3 URA array and MLEM method for a 1275-keV point source... 37

Fig. 2.13. Mechanical reconstructed images using a 5×3 URA array and MLEM method for a 122-keV point source... 38

Fig. 2.14. Mechanical reconstructed images using a 5×3 URA array and MLEM method for a 356-keV point source... 39

Fig. 2.15. Electronic reconstructed images using a 5×3 URA array and MLEM method for a 356-keV point source... 39

Fig. 2.16. Dual reconstructed images using a 5×3 URA array and MLEM method for a 356-keV point source... 40

Fig. 2.17. Mechanical reconstructed images using a 5×3 URA array and MLEM method for a 662-keV point source... 40

Fig. 2.18. Electronic reconstructed images using a 5×3 URA array and MLEM method for a 662-keV point source... 41

Fig. 2.19. Dual reconstructed images using a 5×3 array and MLEM method for a 662-keV point surce. 41

Fig. 2.20. Electronic reconstructed images using a 5×3 URA array and MLEM method for a 1275-keV point source. 42

Fig. 2.21. If the position of the threshold is varied, all other characteristics are changed -TP, FP, TN, and FN and... 43

Fig. 3.1. Active collimator(left) and planar detector(right) of the portable active collimation system. 45

Fig. 3.2. Components of the active collimation camera. 46

Fig. 3.3. Schematic of the active collimation system. 47

Fig. 3.4. Timing histogram of coincident events. 48

Fig. 3.5. Summed energy spectrum of the electronic collimation for a 662-keV point source. 49

Fig. 3.6. Picture of front-end circuit. 50

Fig. 3.7. Drawing chart of the gain and position correction of the first and second detector. 51

Fig. 3.8. Linearity of amplitude circuit. 51

Fig. 3.9. Schematic diagram of front-end circuit. 52

Fig. 3.10. Signals measured by an oscilloscope. 53

Fig. 3.11. Screen shot of Xilinx ISE webpack 9.2. All of the timing information were operated by processing which... 54

Fig. 3.12. Screen shot of Labview programming. 54

Fig. 4.1. Reconstruction images using a 5×3 URA and the MLEM method for a 122-keV point source(mechanical... 55

Fig. 4.2. Reconstructed images using a 5×3 URA and the MLEM method for a 356-keV point source. 55

Fig. 4.3. Reconstructed images using a 5×3 URA and the MLEM method for a 662-keV point source. 56

Fig. 4.4. Reconstruction images using a 5×3 URA and the MLEM method for a 1275-keV point source(electronic... 56

Fig. 4.5. Resolution-variance graph for the point source reconstructed by the MLEM method(5×3 URA). 57

Fig. 4.6. Reconstruction images using a 7×5 URA and the MLEM method for a 122-keV point source(mechanical... 58

Fig. 4.7. Reconstructed images using a 7×5 URA and the MLEM method for a 356-keV point source. 58

Fig. 4.8. Reconstructed images using a 7×5 URA and the MLEM method for a 662-keV point source. 59

Fig. 4.9. Reconstruction images using a 7×5 URA and the MLEM method for a 1275-keV point source(elcctronic... 59

Fig. 4.10. Resolution-variance graph for the point source reconstructed by the MLEM method(7×5 URA). 60

Fig. 4.11. Histograms of maximum pixel values in reconstructed images of a ¹³³Ba point source 63

Fig. 4.12. ROC curve for a 356-keV point source reconstructed by using a 5×3 URA and the MLEM method(50th...(이미지참조) 64

Fig. 4.13. Histograms of maximum pixel values in reconstructed images of a 137Cs point source(이미지참조) 65

Fig. 4.14. ROC curve for a 662-keV point source reconstructed by using a 5×3 URA and the MLEM method(50th...(이미지참조) 66

Fig. 4.15. Reconstructed images by using the MLEM method(50th iteration) for two 356-keV point sources.(이미지참조) 67

Fig. 4.16. Reconstructed images by using the MLEM method(50th iteration) for two 662-keV point sources.(이미지참조) 68

Fig. 5.1. Schematic diagram of a cubic gamma camera system(left). 69

Fig. 5.2. Detectors positioned to cover 2π-scattering angle(right). 69

Fig. 5.3. A schematic showing the active collimation process 70

Fig. 5.4. Images reconstructed with mechanical collimation using a 5×3 URA array and the MLEM method for a... 70

Fig. 5.5. Images reconstructed using a 5×3 URA array and the MLEM method for a 356-keV point source. 71

Fig. 5.6. Histograms of maximum pixel values in reconstructed images of a 356-keV point source 71

Fig. 5.7. Images reconstructed using a 5×3 URA array and the MLEM method for a 662-keV point source. 72

Fig. 5.8. Histograms of maximum pixel values in reconstructed images of a 662-keV point source 72

Fig. 5.9. ROC curve for a point source reconstructed using the MLEM method(50th iteration)(이미지참조) 73

Fig. 5.10. Images reconstructed with electronic collimation using a 5×3 URA array and the MLEM method for a... 73

Fig. 5.11. Reconstructed electronic collimation image of 662-keV point sour.:es at three different positions in a 4π-... 74

Fig. 6.1. Concept drawing of the compact high-resolution active collimation system composed of Cs(T1) coupled... 78

Fig. A1. A compact hybrid gamma camera. 83

Fig. A2. Components of a compact hybrid gamma camera. 84

Fig. A3. Timing histogram of coincidence events. 84

Fig. A4. Reconstructed images using MURA array and MLEM method for a 122-keV point source 85

Fig. A5. Reconstructed images using MURA array and MLEM method for a 356-keV point source. 86

Fig. A6. Reconstructed images using MURA array and MLEM method for a 662-keV point source. 86

Fig. A7. Reconstructed images using MURA array and MLEM method for a 1275-keV point source. 87

Fig. A8. Resolution-variance graphs for a point source reconstructed by the MLEM method. 88

Fig. A9. Histograms of maximum pixel values in reconstructed images for a 356-keV point source. 90

Fig. A10. Histograms of maximum pixel values in reconstructed images for a 662-keV point source. 90

Fig. A11. Histograms of maximum pixel values in reconstructed images for a 1275-keV point source. 90

Fig. A12. ROC curve using MLEM method(50th iteration)(이미지참조) 91

Fig. A13. Reconstructed images using MURA array and MLEM method for a 662-keV multiple point sources(50th...(이미지참조) 91

Fig. B1.(a) Schematic diagram and(b) scattering photon energy spectrum. 94

Fig. B2. Performance evaluation for various inter-detector distances by using the DE, ARM, and FOM for a point... 96

Fig. B3. Performance evaluation for various detector thickness by using the DE, ARM, and FOM for a point source.... 96

Fig. B4. Angular resolution for various distances between the 1st and 2nd detectors by using ARMs in terms of the...(이미지참조) 97

Fig. B5. Evaluation of various uncertainty factors based on ARMs in tenns of the full width at half maximum... 97

Fig. B6. Detection efficiency of the MSCC for various detector materials and inter-detector distances for a point... 98

Fig. B7. ARMs of the MSCC for various detector materials and inter-detector distances for a point source.(right) 98

Fig. B8. Performance evaluation of the MSCC based on FOM for various detector materials and inter-detector... 98

Fig. B9.(a) Visualization of the simulation and(b) reconstructed image using a simple back-projection method with... 98

Fig. B10. Configuration of MSCC detection system for simulation.(left) 100

Fig. B11. Distribution of the 6-MV photon beam of VC2300C/D.(right) 100

Fig. B12. Comparison of the depth dose distributions in water phantom. 101

Fig. B13. Axial combined image for the Head(XZ view). 102

Fig. B14. Coronal combined image for the Head(XY view). 102

Fig. B15. Sagittal combined image for the Head(YZ view). 103

Fig. C1. Configuration of the MSCC detection system.(left) 105

Fig. C2.(a) Reconstructed image, and(b) energy spectrum by using Compton kinematics for the trinitrotoluene. 105

Fig. C3.(a) Reconstructed image, and(b) energy spectrum by using Compton kinematics for the cocaine. 106

Fig. C4.(a) Reconstructed image, and(b) energy spectrum by using Compton kinematics for the nitroglycerine. 106

Fig. C5.(a) Reconstructed image, and(b) energy spectrum by using Compton kinematics for methamphetamine. 106

Fig. C6. Schematic diagram and reconstructed images of hidden substances 107

Fig. C7. Comparison of MSCC and conventional Compton camera. 108

초록보기

A portable active collimator using systematically patterned scintillators was constructed and its performance was evaluated. In the conventional passive radiation collimation method, single or multiple holes are used to limit radiation reaching a detector while radiation scattered in the collimator is not used. However in active collimation where one replaces the passive collimator with a radiation detector, both the radiation that passes through the holes and radiation scattered in the collimator can be used. The active collimator was composed of uniformly redundant array (URA)-pattemed Bi4Ge30i2 (BGO) scintillators with a CsI(Na) detector planar array positioned behind the collimator. Images using radiation passing through the holes of the URA collimator were reconstructed using the correlation method of conventional coded apertures, while the radiation scattered in the active collimator and detected in the planar detector, was imaged using a Compton imaging technique. Since the active collimation method uses both Compton scattered events and photoelectric absorption events, its detection efficiency and energy range are inherently higher than those of conventional collimation methods. The reconstructed images of the portable active collimation methods for various energy sources were obtained and compared with those of conventional methods. Moreover, in order to increase detection efficiency and field-of-view (FOV)? an active collimator and multiple secondary detectors were positioned in a cubic shape. The entire module

forms a cubic structure that generates images on the basis of radiation interactions from every direction. The coverage angle for detecting scattered radiation is 2k with a detection efficiency approximately 17 times higher than previous system that comprised only one pair of detectors.

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