Research On The Influence Of Reflectors Structures And The Scintillators Surfaces Topographies On The PET Detector Performances

As a kind of nuclear medical imaging technology,positron emission tomography(PET)has extremely high sensitivity.PET is able to detect the metabolic process of organs at the molecular level and diagnose tumors and brain cancers in the early stage.The core component of the PET system is the front-end detector,which is responsible for detecting high energy particles and converting the optical signals into electrical signals.With the energy and timing performance of PET detector improving,the final imaging quality of PET system would improve.The front-end detector of PET mainly consists of three parts: the scintillation crystals that intercept high-energy particles and release visible photons,the photon sensors that detect visible photons and generate electrical signals,and the electronic circuit that collects electrical signals and transmits the signals to the computer.In the current PET,the most commonly used scintillation crystal and photon sensor are yttrium lutetium silicate(LYSO),and silicon photomultiplier(Si PM).However,due to the large refractive index of scintillation crystal(refractive index of LYSO is 1.82),the output rate of visible photons is limited,which degrades the performance of the detector.In order to improve the light output,detection efficiency and temporal resolution of the detector,this thesis conducts research from the following aspects: 1)designing composite reflectors which combine two reflection characteristics and testing their energy output performance;2)building optical simulation model of detector and researching the energy extraction efficiency and timing resolution of composite reflectors;3)studying the influence of scintillation crystal roughness on the detector.This thesis designed a variety of reflective layer structures used on scintillators.By using specular reflection and diffuse reflection materials in specific areas of crystal surfaces,the advantages of the two reflection characteristics could be fully utilized to maximize the comprehensive performance of the detectors.And the experiment results proved their effects on improving energy output.The optical simulation model of the detector constructed based on the actual structure,was used to tracing and analyzing the wh designed composite reflectors couldachieve better comprehensive performances compared with single-material reflective layer.The influence of crystal processing technology on the surface topography was researched in this thesis,and the simulation study of its effects on detector performances was carried out.With different abrasive materials used in processing,different surfaces roughnesses were obtained,which could change the detector energy output.