A Study Of Inter-Crystal Scattering Events In PET Detector

PET is a functional imaging technology that can provide the biochemical reaction and metabolic information of tissues and organs in vivo and plays an important role in clinical diagnosis and drug development.In PET detector,the energy of gamma photons will be deposited in multiple channels because of the inter-crystal scattering phenomenon caused by the Compton effect,which can make it difficult to identify coincident events and has a negative effect on the sensitivity and spatial resolution in PET system.In order to improve this situation,the dissertation focuses on the position,energy and time distribution of intercrystal scattering events and proposes a method to find the position of first interaction in inter-crystal scattering events based on the information of energy and time difference.In this work,the inter-crystal scattering events will be studied in simulation and experiment.A 6×6 one-to-one coupled PET detector with LYSO and Si PM is constructed to simulate the process of inter-crystal Compton effect based on Geant4 in simulation,from which two-channel response inter-crystal scattering events deposited in the incident channel of gamma photons and eight channels around it are required.PET detector with the same structure as that in simulation is used to require two-channel response inter-crystal scattering events at the same position through high speed oscilloscope in experiment.Position,energy and time information of these two-channel response inter-crystal scattering events are extracted and analyzed.The results of simulation and experiment show that the position,energy and time distribution of these events have explicit characteristics.Based on the results of simulation and experiment,the relationship between energy and time difference in two-channel response inter-crystal scattering events is studied.According to the conclusion,a method based on energy and time difference is proposed to find the position of first interaction and the experiment shows that the accuracy is 84.1% and the number of valid events increases 15.0% with the method for two-channel response intercrystal scattering events,which has a positive effect for PET system.