Study On The Image Restoration Of γ-Ray Pinhole Imaging System

γ-ray pinhole imaging system is a major approach to diagnose the radioactive source. It mainly comprises four parts: thick pinhole, LSO scintillator, Microchannel-plate image intensifier and CCD camera. The acquired image is degraded due to the limited spatial resolution and random noise of the constituent instruments. In order to improve the image quality and give a better understanding of the radioactive source, this dissertation aims at systematical study on the image restoration of thick pinhole imaging system. The image denoising methods and deblurring methods were respectively proposed according to the properties of point spread function(PSF) and noise. The methods were verified by the application to the pinhole imaging experiment results of 60Co source and rod-pinch-diode. The main contributions of the dissertation can be outlined as follows.1. The PSFs of thick pinhole, LSO scintillator, microchannel-plate image intensifier and CCD camera were obtained through simulation or experiment.2. The cascade model of the detective quantum efficiency was established forγ-ray pinhole imaging system. The model shows that the detective efficiency and modulation transfer function of the thick pinhole are two main factors of the image degradation.3. The image noise is described by gamma noise and Gaussian noise. An adaptive algorithm is proposed to substitute gamma noise with the median of the neighborhood, which achieves satisfactory noise removal. The Gaussian noise is greatly reduced with the locally-adaptive wavelet filter.4. Pixon-based Richardson-Lucy method is proposed to restore the image blurred by LSO scintillator, image intensifier and CCD camera. This algorithm outperforms Richardson-Lucy method on the image improvement and convergency.5. Richardson iterative method is adopted to restore the image degraded by thick pinhole. The stopping rule of the iteration is determined by the simulation results.