Study On Spatial Resolution Of Photoelectricity Radiography System

In this dissertation, the background and significance of the CCD-Based digital X-ray radiography system was stated. The key problem i.e. resolution of the system was theoretically and experimentally studied in detail.Theoretically, the calculating model of scintillator's MTF was established while the principle of the X-ray's action on it was analyzed in the CCD-Based digital X-ray radiography system. On the base of this model, the MTF curve of the scintillator whose materials were CsLTl and BGO(Bi4Ge3Oi2) was calculated, the influence on MTF curve of the parameters including scintillator's thickness, materail and X photon's energy was stimulated. The MTF curve of the coupling lens in the system was calculated with the optical software CAOD while the object distance and the visual field varied. With analyzing the calculating method of the CCD camera in perfect condition, the CCD parameters' influence on MTF was calculated and the sampling frequency's influence on the spatial resolution was analyzed.In experiment part, the result of CCD camera's spatial resolution was got with using identification plate to take photo. In another experiment which used tungsten stage, We captured a great number of images by the system which used the X ray source generated by 12 MeV LIA. To analyzing these images, We exploited an image processing software. In this way, the MTF curve and spatial resolution of the system was got under vary conditions.Finally, the conclusion of this research can be made as followed.1. In the special physical experiment conditions, the system's resolution is mainly restricted by the X ray source, the scattering object and the scintillator. So the total resolution is less than lip/mm. Lens and CCD camera is less effect because of their high resolution which is more than 2 Ip/mm.2. The influence of the X ray source is related with the source' size and the distant from object to scintillator. When the distant is more than 600mm, the system's resolution drop down to less than 0.5 Ip/mm and can not meet the requirement of the radiography system.3. The increasing of scintillator's thickness will reduce the spatial resolution while the increasing of input X photon's energy will raise it. The scintillator made of BGO(Bi4Ge3Oi2) have better spatial resolution than what made of CsI:Tl with same thickness.4. Because of the influence of sampling frequency, the increasing of lens' magnification will reduce the CCD camera's spatial resolution.