【作者】 刘伟；

【导师】 任秋实； 杨昆；

【作者基本信息】 河北大学 ， 仪器仪表工程， 2015， 硕士

【摘要】 本课题来源于医用PET/CT研发项目,该研发项目的是期望通过正电子发射断层成像(PET)与X射线断层成像(CT)两种图像重建方式的集成融合,来实现更高的成像质量,以满足当前不断提升的医疗诊断要求。PET是当今最受关注的医疗设备之一,在技术成熟之后广泛应用于神经疾病、心血管疾病和肿瘤等方面的临床诊断和疗效监测,并不断通过自身技术性能的提升以及与其它成像方式的融合来逐渐成为临床诊断治疗过程中最重要的医疗设备。PET属于核医学领域,它的核心技术之一就是探测器,它是由闪烁晶体和光电倍增管(PMT)耦合而成的一种光电检测设备,它的功能是捕捉来源于示踪剂的正电子湮灭所产生的γ光子,并通过自身的光电转换和信号放大功能将γ光子信号最终转变为可用的电信号,为后期的信号放大和图像重建提供可靠稳定的信号来源。根据PET的原理要求,为了能够捕捉一条直线上运动方向相反的一对γ光子,PET所用探测器通常会成环形布置,这就需要使用大量的PMT。PMT是PET探测器的重要组成部分,起到了PET图像重建信号来源的作用,所以PMT性能的优劣会对PET图像重建产生很大的影响。在PMT众多特性中,阴极均匀性是极为重要的一个,而本文的目的便是通过设计一套检测设备,用于检测PMT的阴极均匀性,对用于PET生产过程中所使用的PMT进行检测。首先本文介绍了PET的基本原理以及PET/CT中两种成像方式的融合,对当前PMT检测所涉及的领域进行了梳理,并对本课题的来源和目的进行了阐述。其次,本文介绍了PET探测器的结构,并对其中所涉及到的示踪剂、闪烁晶体作了介绍,重点分析了探测器中PMT的结构、原理以及较为重要的五个特性,通过特性的分析来说明PMT阴极的重要性。再次,本文重点介绍了整套检测的设备的搭建。通过针对PMT性能特点,确定了检测设备需要暗箱、平移台、光源、数据采集以及相对应的软件等基本组成部分。本文通过单轴平移台等硬件组合搭建了一套二维运动平台作为光源的移动平台,并通过编写上位机实现了检测路径的控制,并进一步实现了扫描精度的可调。光源采用了蓝光LED,通过光阑的限光作用实现了1mm的光束,通过二维平移台的带动,对PMT阴极面进行逐点扫描。为保证数据采集的精度,本文使用了ORTEC核电子学仪器作为实验数据采集分析设备,实现了两级放大、数据累加以及数据分析。最后,通过搭建的测试系统对PET/CT所用的CR260型PMT进行了检测,介绍了测试流程和测试过程中的实现方法,通过MATLAB对所得数据进行拟合,得到了PMT阴极均匀性图像,并对PMT阴极均匀性进行了计算。通过实验,验证了系统的可用性和可靠性。更多还原

【Abstract】 The paper is from the medical PET/CT research and production project, in order to meet the growing medical diagnostic requirements, this R&D project is expected to achieve higher image quality by integration and fusion of two kinds of image reconstruction methods which are Positron Emission Tomography(PET) and X-ray tomography(CT).PET is one of the most popular medical equipment, it’s widely used in neurological diseases, cardiovascular disease and cancer in clinical diagnosis and therapeutic monitoring with its proven technology. It has become the most important medical equipment in clinical diagnosis and treatment through its continuous technical performance improvement and integration with other imaging modalities.PET belongs to the field of nuclear medicine, one of its core technology is detector, which is a kind of photoelectric equipment coupled with scintillation crystal and photomultiplier tube(PMT), its function is to capture gamma photons produced by positron annihilation which produced by radioactive tracer and then turn this signal into practicable electrical signal by electro-optical conversion and signal amplification and provides a reliable and stable signal source for the latter part of signal and image reconstruction. According to the principles of PET, in order to capture a pair of gamma photos with opposite direction, detectors are always arranged in a ring, so lots of PMTs are required.PMT is most important part of a detector used in PET, as the signal source of PET image reconstruction, its performance is extremely important. Among all the features of PMT, cathode uniformity is very important, and the purpose of this paper is to test the cathode uniformity of PMT in the production process of PET by designing a set of inspecting equipment.Firstly, this paper describes the basics of PET and the fusion of PET/CT, lists some former methods of PMT testing, and explains the source and purpose of this paper.Secondly, this paper introduces the structure of PET detector, including radioactive tracer and scintillation crystal, then makes an full introduction about structure and principle of PMT, including five most important features.Thirdly, this paper introduces the testing equipment. Due to the special characteristics of PMT, a project including dark box, translation stage, light source, data acquisition and software has been settled. In this paper, a precision-adjustable two-dimensional translation stage assembled with basic parts is controlled by upper computer written by myself. LED is used in the light source, with help of flare stop, a light beam with diameter of 1mm is satisfactory for the experiment. The light source carried by the translation stage can provides point-by-point scanning. In order to meet the requirements of data acquisition, I used ORTEC nuclear electronic instruments as DAQ part which achieves two-stage amplification, data accumulation and data analysis.Finally, I tested CR260 with this testing equipment and got the data of PMT cathode uniformity. The detailed test procedures are introduced in this paper. A data fitting has been programmed in MATLAB and gave the image of PMT cathode uniformity, and also a calculation of the tested PMT photocathode’s uniformity. Through experiments, system availability and reliability has been verified.更多还原