断层屏蔽SPECT成像法探讨

本文以空间积分原理为基础,以逐渐逼近法为图像重建的核心,探讨了可实现断层屏蔽的SPECT成像的途径.与传统的SPECT成像方法比较,它具有高的灵敏度和数据获取速度快的特点.由于无须用机械装置将γ照相机旋转,消除了运动带来的误差,提高了成像的质量.本文用线性方程组的松弛解法对无散射和无噪音的二维空间的模拟数据进行了验算,证明逐渐逼近法能逐渐逼近到放射性分布区域,并能基本给出分布形式.     

随机中子场探测器效应的影响

用随机中子场下的几率细致平衡主方程讨论了探测器效应对测量结果产生的影响,提出了可用增加探测器对中子的作用几率来减少影响,提高精度。     

天然Cl中子全截面,（n,α）和（n,p）截面的评价

在收集实验数据的基础上，结合理论计算对天然Ｃｌ的中子全截面，（ｎ，α）和（ｎ，ｐ）反应堆面进行了评价，与ＥＭＤＦ／Ｂ－６库推荐结果进行了比较，分析了与Ｂ－６库评价分岐的原因。     

TIME INTERVAL APPROACH TO THE PULSED NEUTRON LOGGING METHOD

The time interval of neibouring neutrons emitted from a steady state neutron source can be treated as that from a time-dependent neutron source,In the rock space.the neutron flux is given by the neutron diffusion equation and is composed of an infinite number of “modes”,EaCh“mode”,is composed of two die-away curves.The delay action has been discussed and used to measure the time interval with only one detector in the experiment,Nuclear reactions with the time distribution due to different types of radiations observed in the neutron well-logging methods are presented with a view to getting the rock nuclear parameters from the time interval technique.     

MC法模拟多路平行束准直器对比度

采用MC法模拟设计了用于SPECT成像的多路平行束(MPB)准直器,将MPB系统重建的模具图像与平行束(PB)系统重建图像进行对比。用OS-EM迭代算法重建图像并计算对比度、信噪比、归一化标准偏差三个指标用于评价图像质量。结果表明:随着迭代次数增加,MPB系统重建图像中热源的对比度高于PB系统,对于小半径热源这个差值更明显,但是冷源的对比度低于PB系统;两个系统有可比较的重建图像收敛速度,随着迭代次数增加,MPB系统的噪声特性略差于PB系统。     

介质中子宏观吸收截面对相邻中子时间间隔的影响

从原理上推导了有介质吸收作用时被探测的相邻热中子时间间隔公式，用改变介质宏观吸收截面的方法，测量了３种不同宏观吸收截面介质时相邻中子时间间隔变化曲线，对原理进行了验证。     

诱发裂变中子场及其功率谱密度比值测量法

用随机过程主方程近似指出诱发裂变发射的中子形成１个随机中子场,随机场内中子的探测器信号具有相关性。提出功率谱密度比值测量法。该比值随裂变核含量与探测器夹角不同有明显变化,与诱发型变发射ｖ个中子的几率分布有关。     

多通道平行束准直器灵敏度补偿性能

点源扩展函数PSF作为SPECT成像的一个重要参考,反映出相应准直器灵敏度和空间分辨率等的特性。本文在多通道平行束准直器MPB的几何框架下进行物理模型构建,解释了由探测器晶体厚度引起的PSF变化以及基于该变化进行的公式修正,指出了不利的因素,其结果与蒙特卡罗模拟基本吻合。在PSF基础上,结合蒙特卡洛模拟,指出了在准直器的拉伸过程中,斜平行束部分OPB的灵敏度变化特性和对准直器的补偿作用;通过两点源逐渐接近的过程,并与高灵敏度平行束准直器HSPB对比,指出MPB准直器在保持高灵敏度下,还能有高空间分辨率的原理,提出了一种设计高灵敏度和高空间分辨率准直器的方法。     

An iterative image reconstruction algorithm for SPECT

Properties of two algorithms for iterative reconstruction of SPECT images, LS-MLEM and LS-OSEM,are studied and compared with the ML-EM algorithm in this paper. By using projection data of heavy-noise, their effectiveness in improving SPECT image quality is evaluated. A phantom with hot and cold lesion is used in the investigation. The reconstructed images using LS-MLEM or LS-OSEM show that there is not a rapid increase in image noise,and the ＂best＂ estimate is assuming that the reconstructed images satisfy the statistical model. The major advantage of using LS-MLEM or LS-OSEM algorithm in SPECT imaging is in their ability to accurately control for heavy-noise. And LS-OSEM algorithm obviously improves the convergence rate.