Research On 3D Image Reconstruction Technology Of γ Camera In Homogeneous Media

With the development of our country’s nuclear technology in recent years, large amounts of radioactive wastes have come to our life and radioactive sources related to nuclear facilities are putting into operating or decommissioning. It’s very important to carry out the investigation of sources, accurate assessment of radioactive nuclear wastes and evaluate nuclear facilities.Gamma camera being an imaging device of gamma ray, is one of the most intuitive instruments which can determine the location of sources and the distribution of pollution from long distance quickly. It plays an important role in many fields such as:planned maintenance, outage of nuclear power reactor; checking the production process of radioactive chemical detection; pipeline measurement; radiation source inventory records before removing; remote survey of radioactive environment; determining the size of shielding; cost benefit of nuclear waste and reduction of cost; reducing the exposure and improving the technology etc..Based on the imaging mechanism of gamma camera, this study proposes a 3D reconstruction technology of gamma camera’s images and design a statistical reconstruction methods based on SPECT image reconstruction algorithm. Richardson iterative algorithm is used to eliminate the PSF caused by thick pinholes. ART and MLEM are used as imaging reconstruction algorithm and the corresponding reconstruction program is written. In the imaging reconstruction, we have designed the physical model of parallel beam and pinhole. With the improvement of medical getting projection data in circle, the projection images are obtained in arbitrary angles and positions in order to consistent with the actual situation extremely. The images’output format as well as 3D reconstruction program and the 3D display program are compiled. The simulation models of gamma camera are established in the Monte Carlo procedure to design experiment and debug program with simulated data. Based on the reconstruction results of simulated technology, two kinds of reconstruction algorithms are compared in accuracy, resolution and response time. At the same time, the existing gamma camera is debugged and 3D reconstruction has been realized using experimental data of gamma camera. From the reconstruction results of the simulated and experimental data, statistical reconstruction algorithm can calculate the accurate position of radioactive sources in a few pictures. On the basis of sources’3D reconstructed positions simulation in Monte Carlo N Particle Transport Code (MCNP) are identical with the actual environment in view of point sources with single and multi-energy:selecting probability function at a particular angle; getting projection data through a series of operations --data conversion, image restoration, image rotation; comparing the experimental and simulated value in the same angle; calculating the relative intensity distribution of sources. At the same time, comparing the calculated intensity distribution with the reconstruction results which is attenuation compensated directly, the experiment and simulated results show that this method with the help of MCNP simulation can accurately reconstruct the intensity distribution of sources. Based on the above results, we concluded that the scheme can reconstruct the exact position and intensity distribution of radioactive sources, which is practical and feasible. Finally, based on the existing technology, reconstruction for shape and center of volume sources in the barrels has been implemented. The MCNP simulation data shows that:MLEM algorithm can accurately reconstruct the 3D distribution of the radioactive sources.