Research On The Surface Reflectors Characteristics Of Scintillator And Method To Obtain The Depth Of Interaction

Positron emission tomography is the most sensitive medical imaging instrument for data display and quantitative analysis of human normal metabolism and pathological changes.It is used for early diagnosis and staging of major diseases such as cancer,heart disease,and nervous system diseases.The detector based on the scintillators is the key component of PET equipment,and the energy resolution and the time resolution of the detector are important for promoting the performance of PET system.The depths of interaction(DOI)between the scintillators and the gamma rays depends on the attenuation of the scintillators,which is random and therefore influence the spatial resolution of detectors.The photons generated by the ? rays and scintillators will be receive by the detectors,and the light transport efficiency and the light extraction affects the time resolution and energy resolution.In order to improve the energy resolution and the time resolution of PET detectors,this paper proposed three contents as following.1)The influence of the reflectivity characteristics of the scintillation surfaces on the light output and the light transport efficiency.2)The impact of the alternative geometric structure of the cubic scintillators on the time performance.3)The method to decode the depths of interaction for ? rays based on the light-shring windows.Based on the surface reflection characteristics of specular reflection and diffuse reflection,three optimization methods were proposed to improve the average light output and light transport efficiency.Method 1 the surface of the crystal was partially warpped with diffuse reflectors while the other was warpped with specular reflectors.Method 2 the layer of Antireflection(AR)coating was added between the diffuse reflector and scintillators.Method 3 the order of crystal and photo sensors in the detectors was changing.The three methods can improve the average light output and light transport efficiency.The effect of alternative the end and the top geometry of the scintillators on the light output and time resolution was studied.For the end of the scintillators,we explored the change of the light output with the increase of the height of the quadrangular pyramid and the radius of the sphere.For the top of the scintillators,four prism cones were designed to concentrate light.Two groups of samples were processed for experimental test,and the results show that the conical structure can effectively improve the light output and time resolution.The method to decode the depth of interaction of the ? rays was present based on the lightsharing windows.The light-sharing windows were opened between the discrete scintillators arrays to guide the distribution of the photons in the scintillators arrays.The distribution of photons in the photo sensors was used to calculate the reaction depths of ? rays.The simulation and experimental results showed that this method can realize the 3D decoding of ? rays.