Design Of Readout Electronics For In-beam PET Of Heavy-ion Cancer Therapy Device

The heavy ion beam,provided by the Heavy Ion Research Facility at Lanzhou（HIRFL）and the Cooler Storage Ring（CSR）of the Institute of Modern Physics of the Chinese Academy of Sciences,is used for tumor radiotherapy,which features the advantages of physics and biology.Heavy ion radiotherapy has been proved to be one of the most advanced and effective technologies in radiotherapy,and has become the forefront of radiotherapy.The domestic Heavy-Ion Cancer Therapy Device（HICTD）built in Wuwei,Gansu Province has obtained the National Medical Device Registration Certificate.In order to further improve the treatment technology and enhance the competitiveness comparing with the world’s first-class heavy ion therapy equipment,it is necessary to continuously develop new technologies for heavy ion therapy.Positron Emission Tomography（PET）installed on the beam line at the treatment site is called in-beam PET（ibPET）,which is a key detector system in the heavy ion cancer treatment device for implementing real-time,fast and accurate image monitoring of the incident beam position and dose when tumors are treated with heavy ions,so as to ensure the safety of patients and the implementation of treatment plans accurately.The factors affecting the performance of the ibPET imaging system mainly include detector performance,readout electronics resolution,and the performance and function of image reconstruction algorithms.Among them,the performance of readout electronics plays a decisive role.The purpose of this dissertation is to design an electronic circuit with high precision,simple structure,excellent performance and reasonable structure to process the signals from detectors in the ibPET imaging system.It is mainly composed of data acquisition unit（DAQU）,coincidence processing unit（CPU）and clock synchronization unit（CSU）.The core part of the system is DAQU.Based on the application requirements of the ibPET imaging system of the heavy ion cancer treatment device,DAQU,the core electronics of the readout electronics system is mainly designed and implemented in this dissertation.The charge and time signals output from the detectors are fed into the DAQU,and the measurements of energy,position and time information of hit event are completed.In this dissertation the high-precision charge and time measurement techniques are studied to ensure measurement accuracy;based on the Field Program Gate Array（FPGA）,the corresponding logic functions and processing algorithms are designed and implemented,and a time-to-digital conversion（TDC）module is developed in the FPGA also.The DAQU electronics includes a preprocessing unit（PPU）and a data processing unit（DPU）.Inverting amplification,filter shaping,analog-to-digital conversion（ADC）technology combined with integral area algorithm are used for charge measurement;fast amplification,leading-edge discrimination combined with TDC technology are employed for time measurement.Based on the research results mentioned above,the DAQU electronics has been developed successfully and corresponding test and verification work have been carried out.The inherent resolution of charge measurement and time measurement accuracy are better than5.5‰FWHM and 300 ps FWHM respectively.The results show that the intrinsic properties of electronics are better than the application requirements.After that,a detection system was built up combining with detectors,and the system-level test was performed using a²²Na source.The energy resolution of the entire system is 14%FWHM@511 keV,and the resolution of coincidence time measurement is better than1.12 ns.The Flood Map statistics show good position identification capabilities,and484 crystals in the LYSO crystal array detector can clearly distinguished.DAQU’s electronic functions and performance meet the application requirements.