Polarization Tomography of Quantum Radiation: Theoretical Aspects and Operator Approach

We present theoretical foundations for the quantum tomography of polarization states of light fields as a method for measuring their polarization density operator , which characterizes only the polarization degrees of freedom of the radiation. We mainly attend to the method in which the tomographic observables (the “measurement instruments”) are polarizable in nature. We show that the quantum nature of this method can be adequately expressed using the quasispectral tomographic decompositions of in special operator bases, which are finite sums of partially orthogonal projection operators determining the probability distributions of tomographic observables as the decomposition coefficients. We obtain the matrix versions of such “tomographic” representations of , in particular, by projecting them on semiclassical operator bases determining the polarization quasiprobability functions. We briefly discuss the information aspects of the schemes considered in the paper. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 145, No. 3, pp. 344–357, December, 2005.     

针孔单光子发射计算机断层成像的空间分辨率研究

针孔单光子发射计算机断层(SPECT)成像的空间分辨率通常是根据Anger经验公式来进行估算,与实际测量存在较大偏差.本文通过对针孔成像的物理过程进行分析,提出了一个近似度更高的计算公式.利用精确的蒙特卡罗方法模拟针孔SPECT成像,采用OSEM(ordered subsets expectation maximization)算法对投影数据进行图像重建,并与模具实验进行比较,验证了理论公式的适用性.同时还讨论了体素尺寸、几何映射获取投影矩阵以及探测器尺寸与成像物体尺寸比值对断层图像空间分辨率的影响.实验结果显示,该理论公式所估算的空间分辨率比实验值平均偏小约10%,而Anger经验公式所估算的空间分辨率比实验值平均偏大约60%.因此,该理论公式能更好地估算针孔SPECT成像的空间分辨率,可为针孔SPECT系统的设计和使用提供有价值的参考.     

聚合物泡沫结构及密度分布的相衬CT表征技术

阐述了利用X射线相衬成像技术研究高分子有机泡沫材料微观结构的原理及方法,理论分析及实验结果表明,X射线相衬成像方法可以在相当大的程度上提高低Z聚合物泡沫材料的成像衬度。将相衬成像技术与计算机层析成像技术相结合,获得了泡沫样品的3维骨架结构分布,同时,提出利用统计切片骨架"粒子"质心分布的方法来表征其密度分布均匀性。结果说明,该方法能够在微观层次上实现对泡沫样品3维密度分布的完备表征。     

基于最小区域的锥束ART算法快速图像重建

针对锥束ART算法重建速度慢的问题,考虑到工业CT重建目标尺寸差异较大的特点,提出了一种基于最小重建区域的快速三维图像重建方法。由不同视角下的锥束投影构建最小区域包络,对最小区域包络进行膨胀处理,以消除重建目标边界附近所出现的伪影,在此基础上,给出了射线穿过最小重建区域的体素索引及权因子的计算。该方法能够根据重建目标的尺寸自适应地确定最小重建区域,从而最大限度地减少了计算量。实验结果表明,该方法不仅大幅度提高了锥束ART算法的重建速度,而且有效地提高了重建质量。     

OCT图像法测量折射率

基于光程匹配原理提出了一种用光学相干断层成像(OCT)系统获得的图像测量样品折射率的方法。通过分析光程匹配原理,给出用OCT图像法测量样品折射率的原理及过程。以玻璃载波片和黄瓜组织为样品进行实验。实验结果表明,用OCT图像法获得的载玻片和黄瓜组织的折射率测量值分别为1.499和1.353,与发表或已知的折射率结果相吻合,测试结果的随机误差可小于0.01。另外,使用OCT图像法通过短时间所采集的两幅图像可对横向扫描任意位置的折射率同时进行测量。该方法进一步简化了基于光程匹配原理的折射率测量法的过程,缩短了测量时间,是一种快速测量样品折射率的实用方法。     

一种可在线更新的PET实时查找表电路的设计与实现

介绍了一种正电子发射断层成像术实时查找表电路。该电路接收符合电路输出的位置信号和能量信号,用查表的方法完成重心法中的除法运算,然后再第二次查表得到该γ光子所入射到的晶格的离散化坐标值和能量阈值,并完成能量甄别以剔除部分散射事件。此外,该电路还结合了呼吸门控和心电门控功能。查找表存储在flash器件中,由CPLD控制读写。本设计的特点是利用硬件电路来完成查找表功能,效率更高,每次事件的查表寻址的延迟时间小于100ns,并且可以在线更新查找表的内容,使用方便。另外,还说明了用CPLD来读写NORflash的方法,以及该电路与系统中其它模块间的数据通信方法。     

An algorithm for computed tomography image reconstruction from limited-view projections

<正>With the development of the compressive sensing theory,the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology.This paper develops an iterative algorithm for image reconstruction,which can fit most cases.This method gives an image reconstruction flow with the difference image vector,which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough.Then the l_2-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles.The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data.Moreover,all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed.     

QGP tomography with photon tagged jets in ALICE

γ＋jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies.Tagging events with a well identified high p T direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon in ALICE,allows us to determine,with a good approximation,both the jet fragmentation function and the back-to-back azimuthal alignment of the direct photon and the jet.Comparing these two observables measured in pp collisions with the ones measured in AA collisions will reveal the modifications of the jet structure induced by the medium formed in AA collisions and consequently will infer the medium properties.     

大气Ring效应差分截面的计算

基于差分吸收光谱算法,使用卫星数据反演大气NO2和SO2等痕量气体柱浓度的时候,Ring效应是影响反演结果精度的一个重要因素。Ring效应是指:受太阳表面大气消光效应影响,产生称之为夫琅禾费线的暗线结构,而由于太阳光在地球大气中传输引起非弹性散射,导致观测到的夫琅禾费线变短,这个结果可以近似地认为是对夫琅禾费线的填充。研究表明,大气中的N2和O2分子的转动拉曼散射是导致Ring效应的主要原因。利用星载传感器OMI/AURA测量的太阳光谱和N2和O2分子的转动拉曼散射截面卷积,除以原始太阳光谱,再经过差分计算,可以获得Ring效应的差分截面,以用来反演痕量气体的浓度。计算的结果与利用辐射传输方程得到的结果比较,相关系数R2达到了0.9663,表明二者基本是一致的。