【作者】 李英帼；

【导师】 李公平； 尹永智；

【作者基本信息】 兰州大学 ， 核科学与技术， 2023， 博士

【摘要】 正电子发射断层显像(PET)设备是临床疾病诊断和基础医学研究的重要工具。由于飞行时间TOF技术、图像重建算法等研究的不断深入,PET成像性能已取得了长足进步,但是具有射线作用深度校正的DOI-PET技术仍是当前PET研究的重要工作。本论文设计了两种亚毫米分辨率的正交条形碲锌镉探测器,提出了一种基于信号波形的碲锌镉三维位置计算方法,实现了碲锌镉探测器对伽马射线作用三维位置坐标的精确测量,完成了伽马射线DOI探测。本论文完成了碲锌镉半导体探测器与硅酸钇镥闪烁体探测器PET符合成像实验,得到了亚毫米高分辨率的PET成像结果,验证了使用亚毫米分辨率正交条形碲锌镉探测器开展高分辨率DOI-PET成像的可行性。本论文以micro-TCA架构的高速数字化波形采集系统为核心,采用在板FPGA Xilinx V6编程完成PET成像算法设计和验证,基于MATLAB/Simulink和Sys gen编程环境,编写了基线恢复、信号识别与寻峰、符合逻辑等信号处理模块,完成了数字信号处理建模和仿真,发展了碲锌镉半导体与硅酸钇镥闪烁体的快慢符合成像。本论文使用信号波形采集,以碲锌镉探测器的阳极输出信号进行事件分类,重建了单阳极事件、相邻阳极电荷共享事件和非相邻阳极康普顿事件。使用三维坐标公式计算了511 ke V湮灭辐射的三维位置,与神经网络算法得到的三维位置坐标符合较好。1.0 mm正交条形碲锌镉探测器单阳极事件能量分辨率达到2.7%;相邻阳极电荷共享信号相加能谱能量分辨率为5.8%;非相邻阳极康普顿散射信号相加能谱能量分辨率为6.3%。0.4 mm超高分辨率碲锌镉探测器采用0.3 mm阳极条和0.9 mm阴极条设计,电极间隙均为0.1 mm。使用Comsol软件分析了探测器的电场和权重电势,证明了0.4 mm探测器较小阳极条具有良好的小像素效应。0.4mm碲锌镉探测器的单阳极、相邻阳极和非相邻阳极事件的能量分辨率分别为6.5%、4.6%和8.5%。0.4 mm碲锌镉探测器单阳极事件能量分辨率良好,证明该探测器的正交条形设计是成功的。相邻阳极信号加和能谱显示良好的能量分辨率,且相邻阳极电荷共享显示明显的直线分布,为碲锌镉探测器PET成像的信号插值提供了重要依据。为了测试碲锌镉探测器的PET成像性能,本论文选取1.0 mm硅酸钇镥闪烁体探测器与1.0 mm和0.4 mm碲锌镉探测器进行了PET符合成像,通过旋转平台对直径为3 mm的Na-22点源完成了PET断层成像。结果显示,1.0 mm碲锌镉探测器PET成像能够对相距7 mm的两个Na-22点源实现良好区分,单阳极事件重建图像分辨率为3.1 mm半高宽,相邻阳极事件重建图像分辨率为3.2 mm半高宽。相邻阳极事件在PET图像重建中的引入,使碲锌镉PET成像计数率提高了1.7倍。0.4 mm碲锌镉探测器对Na-22点源的PET成像显示单阳极事件重建图像分辨率为3.0 mm,相邻多阳极事件重建图像分辨率为3.1 mm,相邻多阳极事件的引入使PET成像计数率提高了1.8倍。本论文成功使用亚毫米高分辨率三维正交条形碲锌镉探测器开展了PET成像实验研究,证明了使用碲锌镉半导体探测器开展高分辨率DOI-PET成像的可行性,为碲锌镉半导体PET设备的开发奠定了基础。更多还原

【Abstract】 Positron emission tomography(PET)devices are important tools for clinical disease diagnosis and basic medical research.With the continuous advancement of research in time-of-flight(TOF)technology,image reconstruction algorithms,and other areas,PET imaging performance has made significant progress.However,depth-of-interaction(DOI)correction,which accounts for the effect of radiation penetration depth,remains an important aspect of current PET research.In this paper,two submillimeter-resolution cross-strip cadmium zinc telluride(CZT)detectors are designed,and a CZT-based three-dimensional position calculation method using signal waveforms is proposed.This method enables accurate measurement of the 3-D position coordinates of gamma ray interactions within the CZT detector,thereby achieving gamma ray DOI detection.The paper also successfully uses CZT semiconductor detectors with yttrium lutetium oxyorthosilicate scintillation detectors for PET imaging experiments,obtaining submillimeter high-resolution PET imaging results.This validates the feasibility of utilizing submillimeter-resolution cross-strip CZT detectors for high-resolution DOI-PET imaging.This paper focuses on a high-speed digital waveform acquisition system based on the micro-TCA architecture.The PET imaging algorithm design and verification are accomplished by programming the on-board Xilinx V6 FPGA.Signal processing modules such as baseline restoration,signal identification and peak finding,and coincidence logic are implemented using MATLAB/Simulink and Sys gen programming environments.Digital signal processing modeling and simulation are performed,and a fast-slow coincidence imaging technique combining cadmium zinc telluride(CZT)semiconductor detectors and yttrium lutetium oxyorthosilicate scintillation detectors is developed.Signal waveforms are acquired,and the anode output signals from CZT detectors are used for event classification.Single anode events,neighboring anode charge sharing events,and non-neighboring anode Compton events are reconstructed.The three-dimensional positions of 511 ke V annihilation radiation are calculated using a three-dimensional coordinate formula,and the obtained positions show good agreement with those obtained through neural network algorithms.The 1.0 mm cross-strip cadmium zinc telluride(CZT)detector achieves an energy resolution of 2.7% for single anode events.The energy resolution for neighboring anode charge signal summation spectra is 5.8%,and for non-neighboring anode Compton events,it is 6.3%.The 0.4 mm ultra-high-resolution CZT detector is designed with 0.3 mm anode strips and 0.9 mm cathode strips,with an electrode gap of 0.1 mm.The detector’s electric field and weighting potential are analyzed using Comsol software,confirming the small pixel effect of the 0.4 mm detector with smaller anode strips.The energy resolutions for single anode events,neighboring anode events,and non-neighboring anode events in the 0.4 mm CZT detector are6.5%,4.6%,and 8.5% respectively.The good energy resolution for single anode events in the 0.4 mm CZT detector demonstrates the success of the cross-strip design.The neighboring anode signal summation spectra show excellent energy resolution,and the distribution of charge sharing between neighboring anodes displays a clear linear pattern,providing important basis for signal interpolation in CZT detector PET imaging.To evaluate the PET imaging performance of the CZT detectors,this paper conducted PET coincidence imaging using a 1.0 mm yttrium lutetium oxyorthosilicate scintillation detector,a 1.0 mm CZT detector,and a 0.4 mm CZT detector.A rotating platform was used to perform PET tomography imaging of a 3 mm diameter Na-22 point source.The results showed that the 1.0 mm CZT detector PET imaging achieved good differentiation between two Na-22 point sources separated by 7 mm.The reconstructed image resolution for single anode events was 3.1 mm full width at half maximum(FWHM),and for neighboring anode events,it was 3.2 mm FWHM.The introduction of neighboring anode events in PET image reconstruction improved the sensitivity of the CZT PET imaging system by 1.7 times.The 0.4 mm CZT detector exhibited improved PET imaging of the Na-22 point source.The reconstructed image resolution for single anode events was 3.0 mm FWHM,and for neighboring multiple anode events,it was 3.1 mm FWHM.The image resolution significantly increased,and the introduction of neighboring multiple anode events improved the system sensitivity by 1.8 times.This paper successfully conducted PET imaging experiments using submillimeter high-resolution three-dimensional cross-strip CZT detectors.It demonstrated the feasibility of utilizing CZT semiconductor detectors for high-resolution DOI-PET imaging and laid the foundation for the development of CZT semiconductor PET devices.更多还原