부호화 구경기반 감마선 영상장비 개발

Abstract

In this study, we analyze radiographic imaging technology and imaging equipment capable of visualizing radioactive materials. First, the pattern of the encoding diameter was determined as the ‘centered mosaic’ MURA pattern, and the corresponding decoding pattern was designed. The optimal thickness of coded aperture was derived by inputting the pattern of the adopted size, material, rank of coded aperture, energy of incident gamma rays (100 keV, 662 keV, 1330 keV), detector size, and scintillation size as parameters. The images of radiation sources obtained as a result of MCNP simulation were reconstructed through the cross-correlation method and the MLEM method. And reconstructed image was evaluated with peak signal to noise ratio (PSNR), normalized mean square error (NMSE), and structure simulation (SSIM). As a result of the evaluation, the image quality of the reconstructed image was 2 ~ 5cm when the MLEM technique was used. In addition, the minimum detection activity at the corresponding thickness was derived, and when the thickness of the encoding diameter was 2cm, the minimum detection activity was 2000counts. Based on the MCNP simulation results, a real system was constructed, and GAGG (Ce) was adopted as the scintillator in consideration of physical characteristics, and SiPM was used as the sensor. The coded aperture adopted a method of inserting tungsten pieces into the results output through a 3D printer, and the radiation signal processing board consisted of an analog board, an ADC+digital board, and a power board. In the real system, the gain of each pixel of the SiPM array was calibrated for a different value, and homography was applied to prevent distortion between the radiation image and the optical image. After constructing the real system, the image quality was evaluated by obtaining an image by increasing the thickness of the coded aperture to 0.5 ~ 4.5cm for verify the MCNP simulation result. Image quality was evaluated at the derived minimum detection activity. Both experimental results confirmed that they had a similar to the MCNP simulation results. In addition, an experiment was conducted to evaluate spectrum characteristics, equipment performance characteristics, and image quality characteristics required by gamma-ray imaging equipment. The spectral characteristics were evaluated with energy resolution, peak-to-valley ratio (PVR), and peak-to-Compton ratio (PCR), and the equipment performance characteristics were evaluated with angular resolution, field of view (FOV), total sensitivity, and image sensitivity. And the image quality characteristics were evaluated by PSNR, NMSE, and SSIM. As a result of evaluating the energy spectrum characteristics in the real system, energy resolution was 8.3%, PVR was 9.494, PCR was 5.06, and angular resolution was determined to be 6 ~ 7° and FOV was 45°. Total sensitivity was calculated as 17.827cpm/nSv/h for , 110.267cpm/nSv/h for , and 7.07cpm/nSv/h for . And image sensitivity within 10 seconds in a 662keV 0.3μSv/h irradiation environment. The image quality of the reconstructed image was 45.886dB, 2.0568 × 10, 0.9917 for each indicator of PSNR, NMSE, and SSIM.