Method Research On High-speed Data Readout Of Digital In-beam PET System

Heavy-Ion Medical Machine(HIMM),designed by the Institute of Modern Physics,Chinese Academy of Sciences,is one of the most effective technical equipment in cancer radiotherapy,which is used for noninvasive precision treatment of cancer,and got national medical device certificate in 2019.A new application field of nuclear technology for civilian use has been opened in my country with the operation of HIMM successfully.Cancer cells can be effectively killed by utilizing the Bragg Peak generated when heavy ion beam passes through the human body and the relative biological effectiveness(RBE),also combining precise detection of the irradiation dose and beam distribution in the target area using the real-time imaging technology,the treatment for patient can be performed safely and accurately.A positron emission tomography(PET)located on the beam line of HIMM,called as in-beam PET,can supply the imaging references for precision radiotherapy using heavy ion,and reduce some influences caused by the uncertainty of the range of heavy ion in non-uniform tissue,the distortion of the dose distribution caused by the movement of the target area,and the treatment risk caused by unreasonable indications.It is only noninvasive check method used at irradiation site.The structure of full digital system of in-beam PET is tree like.Dual-Head Planar-Type detector array looks like a node of leaves,which catches photons produced from annihilation events at target area site,and convert them into electronical pulse signals.These pulse signals are continuously fed to data acquisition units(DAQUs),which play the role of the branches of a tree.The time and energy information of annihilation event is acquired by DAQU.The information from all DAQUs are collected into the central processor module(CPM)which is used as trunk of the tree,and at there the event data are processed and coincidence events are identified.And then,obtained coincidence events are uploaded to host computer to complete image reconstruction.A clock and synchronization unit(CSU)supplies clock signal to all modules in system,to ensure the consistency of time in signal measurement.The high speed data readout method applied in in-beam PET is core technology for realizing the function of system.It can be realized that the acquisition of all events from detector array and discrimination of annihilation events on line through the design of real time signal processing algorithm and high speed communication techniques among nodes in the tree structure,which can effectively support the requirement of the real time image reconstruction in in-beam PET during treatment.In order to realizing the role of imaging for real time monitoring during treatment,and to perform real time reading of signals waveforms from detector array,information extraction and identification of coincidence events in annihilation events on line,the research on the high-speed data read-out method is implemented based on the current all-digital system of in-beam PET in this article,which can reduce time for signal measurement and processing.The high speed data readout method studied by this paper is composed of the real time processing algorithm for digital event and Gigabit high speed communication control technology.For reading and processing the signals from front end detector,a digital timing algorithm and optical fiber transmission links are designed for DAQU,the full digital acquisition capability and data transmission bandwidth of front end circuit are improved.For CPM module,the function of high speed data processing for multichannel is realized,which includes the setting up of optical fiber data communication network connected with multiple DAQUs,the real-time sequencing method of events and identification of coincidence events online,high-speed data interaction via Peripheral component interface express(PCIe),and host computer control,etc.The read-out method introduced in this paper has been used in current PET system with 8 input channels receiving signals from the front-end detector array,each channel can withstand an event rate of 1MHz,for supporting the real-time acquisition,sequencing,all events uploading and corresponding control work.Also,it has successfully passed the test performed in labaratory and on the beam line of HIMM separately.The optimal time resolution of digital timing method designed by us can reach 21 ps,the sorting algorithm can support real-time processing of events upto a count rate of8 MHz at present,and the high-speed communication module achieves a maximum data upload rate of 20 Gbps,which effectively guarantees the engineering requirements for high-speed data readout of in-beam PET system.