Study Of Spatial Resolution Measurement Methods And Simulation Of Detector For Micro-CT System

Micro-CT technology realizes three dimensional imaging of the inner structure of testing objects with micro spatial resolution under nondestructive conditions,so it is widely used in MEMS technology,new materials,electronic science,new materials,biological medicine,and other fields.The specifications of Micro-CT,especially the spatial resolution and density resolution have become issues of concern for researchers,but there are no uniform standards for measurement methods at home and abroad.Besides,how to improve the resolution of Micro-CT is a research focus currently.The detector is a key device of Micro-CT,thus has important influence for the improvement of the system resolution.Scintillator is an important part of the detector.When X ray interacts with the scintillator,scattering,aberration and depth of focus degrade the image quality,and the above factors relate to the thickness of the scintillator,so it is vital to study the relationship between the thickness of scintillator and the image quality.Based on the resolution measurement and detector simulation of Micro-CT,this paper carried out the following work:1.Give a brief review of the origin and development history of CT and give an introduction of the Micro-CT structure.The two important specifications of spatial resolution and density resolution to evaluate Micro-CT are illustrated briefly.2.Put forward some improvements about the straight edge and circle edge ESF methods to calculate MTF.The improved algorithms correct the phantom placement errors and reduce noise,thus increasing the resolution measurement accuracy.The feasibility of the improved algorithms is verified by comparing the resolution calculating by the algorithm and the visual observation result of the bar pattern.Furthermore,the improved algorithms are integrated into a spatial resolution measurement module under the Visual Studio 2010 enviroment.3.A novel three dimensional spatial resolution measurement phantom design is proposed based on the existing spatial resolution measurement methods.The spatial resolution within the x-y plane and along z direction can be measured simultaneously by the phantom.The phantom can also be used to explore the spatial variation of resolution.A simplified phantom is fabricated by excimer laser processing technology.The MTF curve is obtained by the reconstructed CT image.By comparison of the resolution results of the two methods,the feasibility of the pahantom design is verified.4.After weighing the pros and cons of various density resolution meansurement methods for Micro-CT,the density difference method is applied to meassure the density relolution.Two density contrast phantoms are made with Sodium chloride solution and density resolution of the Micro-CT is measured afterwards.5.Conduct exploratory optical simulaiton about high resolution opto couple detector.Build simplified optical path with thin lens instead of the objective lens and the lens in ZEMAX.The depth of focus is obtained according to point spread function and compared to the theoretical result.Build actual optical path in non-sequential mode,and design source to simulate a layer of the scintillator.Put the source at different positions and observe the imaging at the detector.The simulation has important significance for the study of the impact of the scintillator thickness on the imaging results.