Research Of Singles Processing Electronics For The Small Animal PET

Positron Emission Tomography(PET)is one of the most advanced nuclear medical imaging techniques.It injects radiolabeled molecular contrast agents into an organism,measures the γ-rays produced by the agents with detectors,and obtaines images of the distribution of radionuclides in organs or tissues and their variation over time.PET imaging technique has become an important research tool in clinical medical diagnosis and biomedical field.As an important application of PET imaging system,small animal PET has become a research hotspot in recent years.Compared with regular PET imaging systems,a higher resolution is needed to observe smaller animal tissues.The performance of small animal PET imaging system is influenced by detector,electronic resolution and image reconstruction algorithm.For high-precision small animal PET detector,it needs high-precision electronics to process the signal.Therefore,it is quite important to devote effeorts to research the readout electronics with a simple structure and high precision.The electronics of small animal PET usually consists of preamplifers,singles processing electronics,and coincidence electronics,in which the singles processing electronics is the key part.In this paper,singles processing electronics is designed for a high performance small animal PET.This electronics is responsible for charge and time measurement of output signals from SiPM(Silicon Photon Multiplier),and calculates the energy,charge and time information of the events produced by the detector.In this paper,efforts were devoted to study the high precision charge and time measurement for small animal PET,and design the data processing and controlling logic in the FPGA(Field Program Gate Array)device.The time measurement is baesd on the analog summation,leading time discrimination and Time to Digital Conversion(TDC),while the charge measurement is baesd on the amplification,shaping,waveform digitization and digital waveform area calculation,in order to improve the energy measurement precision.Based on the above research,the singles processing electronics is designed and tested.The test results indicate that with an input signal amplitude of 2 V,the charge measurement resolution is better than 3 ‰ Full Width at Half Maximum(FWHM),the time resolution is better than 300 ps FWHM,and the position resolution is better than 3 ‰,satisfying the application requirement.Intial comssioning tests combined with the detector was also conducted,and the test results show that the electronics function well and its performance meets the requirement.This dissertation is organized as follows.Chapter 1 introduces the working principle and application of PET imaging system,as well as its research history.Aiming at signal readout of small animal PET,Chapter 2 reviews the main charge and time measurement methods.And several typical electronics designed for small animal PETs are presented and discussed.This provides important reference for my research in this dissertation.Chapter 3 elaborates on the design of the circuits in singles processing electronics,circuit simulation and key parameters,and selection of kernel devices.Chapter 4 presents design of the signal processing and controlling logic in singles processing electronics,including digital summation,FPGA TDC,data processing and correction in various operation modes,interface logic based on UDP protocol,etc.Chapter 5 is the testing work on the electronics,both in the laboratory and also with the detectors.The results indicate that the electronic performance meets the application requirements.Chapter 6 summarizes this dissertation and outlines plans of future work.