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Improvement Compton Imaging System Based on Semiconductor Detectors

Niknami, Mostafa | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52994 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Hosseini, Abolfazl; Ebrahimi Loushab, Mahdi
  7. Abstract:
  8. Compton imaging is an imaging technique in which Compton scattering is used to produce images from a gamma-ray source. Compton imaging systems are also known as Compton cameras. The basic design of Compton imaging systems consists of two-position detectors that are sensitive to the position and energy scattered from gamma rays. The gamma rays collide with the Compton scatterer detector and the scattered photons are absorbed in the absorber detector. Compton imaging performs well the ground radiation during the scattering processes through the separation of energy. The quality of images produced by Compton imaging depends on a variety of factors including detector energy resolution, efficiency, and spatial resolution of the detector which is a function of the scattering angle. Compton camera efficiency is defined as the fraction of photons entering the scatterer detector that undergoes only one Compton scattering and is then photoelectrically absorbed in the absorber detector.The main purpose of this study, the image improvement in the Compton imaging system is using semiconductor detectors to investigate the effective parameters on efficiency.In this research, The GEANT4 toolkit is used to simulate the Compton imaging system. In the first part of the research,To investigate the efficiency two scatterer and absorber detectors were separated from each other with dimensions and the array of detectors with dimensions as well as scatterer detector Si and absorber detector Ge were selected. Then to optimize the efficiency, Change the parameters of including source distance to the scatterer detector, The distance between the two detectors, dimensions and thickness of the absorber and scatterer detectors, the energy of radioisotope, change of semiconductor type scatterer and absorber detectors and the number of scatterer detector layers by keeping the other parameters constant, a new design with optimal values of efficiency for image enhancement was introduced in the Compton imaging system. Introduced in the design, according to the optimal results obtained from the efficiency values, 8 scatterer detector layers with distance from type Si and absorber detector with array from type Ge and from the last scatterer and arraying scatterer and arraying absorber detectors were selected. Reason for choosing 8 scatterer detector layers, Reduce the events that have caused more than one Compton to scatter in the scatter detectors. The statistical error was less than 3 % in all simulated for efficiency. In the second part of the research, The image reconstruction was performed analytically for the introduced design. According to the results, The value FWHM, is reported with angular uncertainty for energy 0/662 MeV. In the third part of the research, Image noise reduction for an image taken by a human volunteer who was injected with a radioisotope. Reduce image noise to wavelet transform, for an image taken by a Compton camera of a human volunteer injected with Radioisotope and . According to the results, For Level 1 decomposition and Daubechies wavelet family selection of order 1 (db1), The SNR error percentage for the image before and after the noise removal was 7/87 and 8/25, respectively
  9. Keywords:
  10. Wavelet Transform ; Efficiency ; Semiconductor Detectors ; Image Enhancement ; Image Reconstruction ; Comptom Imaging ; GEANT4 Toolkit

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