Study On The Characteristics Of New Scintillators In Micro-CT High Resolution Radiation Detector

Micro Computed Tomography technology(Micro-CT),based on the principle of X-ray imaging,can achieve micro-nano-resolution imaging of the internal structure of the measured object non-destructively.It has been widely used in medical,aviation,materials,petroleum geology and other fields.As an important part of Micro-CT system,the imaging resolution and quantum detection efficiency of radiation detectors will directly affect the key performance indicators of the Micro-CT system such as spatial resolution,imaging signal-to-noise ratio and detection efficiency.As the core component of radiation detector,scintillator’s material density,physical size and luminescence spectrum and other characteristics are one of the main factors that determine the performance of detector.Therefore,in-depth study and discussion of the characteristics of scintillators is of great significance for the research and understanding of radiation detectors,and thus has important application value and academic value for improving the performance of Micro-CT.This thesis focuses on the research on the characteristics of the new scintillator material cerium-doped gadolinium gallium aluminum garnet(GAGG)with excellent comprehensive performance.The relationship between the thickness of GAGG scintillator and X-ray absorption efficiency,X-ray photoelectric conversion efficiency and the spatial resolution of the detector is emphatically analyzed,and proposed a method to correct the crosstalk noise of high-resolution CCD radiation detectors.The main research contents are as follows:(1)The luminescence and fluorescence transmission characteristics of GAGG scintillator were analyzed,and the GAGG scintillator was modeled and simulated by Monte Carlo simulation software EGSnrc.The relationship between the thickness of GAGG scintillator and the X-ray absorption efficiency under different X-ray energy was calculated theoretically.The fluorescence detection efficiency of GAGG scintillator emitted by the detector unit was modeled and simulated by using Zemax optical simulation software,and the relationship between the thickness of the GAGG scintillator and the X-ray photoelectric conversion efficiency was calculated.The approximate relationship between the thickness of GAGG scintillator and the spatial resolution of detector was obtained by using Zemax simulation,which provides a theoretical basis for the geometric size design of scintillator in high-resolution CCD radiation detectors.(2)The crosstalk noise correction method of high resolution CCD radiation detectors was proposed.Through the joint simulation of Monte Carlo program Dosxyznrc and Zemax program,the crosstalk function(CTF)between the pixels of the GAGG scintillator through the optical silicon-lipid coupled CCD detector was calculated theoretically.Then,with CTF as the convolution kernel,the Lucy-Richardson deconvolution operation was used to correct the crosstalk of the projection data collected by the detector.(3)A high-resolution CCD radiation detectors experimental platform was built to test the relationship between the output image gray value of detector and the thickness of GAGG scintillator under different X-ray energy.Then,the crosstalk correction was performed on the projection data of the duplex-wire image quality indicator and pencil collected by the GAGG scintillator detector.The influence of the crosstalk correction on the imaging quality of the detector was analyzed by the gray contrast curve and the modulation transfer function(MTF)curve.