正电子发射型计算机断层成像技术

 正电子发射型计算机断层成像(positronemissioncomputedtomograph简称PET),其原理是将含有发射正电子的放射性核素,如18F、11C、15O、13N等显像剂注入或吸入人体,通过探测正电子放射性核素衰变时产生的正电子与组织内电子湮灭产生两个能量相等、方向相反的γ光子,由计算机重建图像,显示人体代谢和生化等改变,被誉为活体的分了断层图像。因此PET能将人的思维、行为和脑化学联系起来,探讨、解释和定位人脑的功能活动,对于许多精神、情感、功能及运动障碍等功能性疾病,PET具有理论意义和实用价值。     

皮肤微循环无损伤光学成像技术的新进展

微循环信息的获取对于各类疾病的诊断和治疗有着及其重要的作用。皮肤微循环无损伤成像技术取得了很大的进展,出现了各种非光学方法(核磁共振成像、正电子发射断层成像术、超声波成像等)和光学方法(共焦显微镜、光学相干断层摄影术、新型的正交偏振光谱成像技术等)。主要介绍了皮肤微循环无损伤光学成像技术的新进展。     

X射线成像技术在医学中应用

文章介绍了在医学中广泛应用的二维X射线摄影屏一胶片系统及三维计算机断层扫描成像技术。并对二维X射线摄影技术的发展，例如数字减影血管造影（DSA），计算机放射成像（CR）和直接数字化X射线摄影（DR）以及三维成像新技术，如螺旋计算机断层扫描技术（螺旋CT），正电子发射体层／多层螺旋CT图像融合扫描装置（简称PET-CT）和相位衬度成像技术的原理和应用作了简单描述。医学图像后处理是现代医学图像设备不可或缺的组成部分，先验医学知识的融入使现代图像设备具有辅助诊断的能力。     

数据插值对正电子发射断层成像设备的图像重建影响的研究

正电子发射断层扫描(positron emission computed tomography, PET)是核医学领域最先进的临床检查影像技术. PET技术是目前临床上用于诊断和指导治疗肿瘤的最佳手段之一. 正电子发射断层成像设备探测器采集到的数据需要进行数据处理, 把原始数据转换成正弦图形式的数据才能用于图像重建. 平行束断层重建和扇形束图像重建是图像重建的两种方法, 分别对应平行束和扇形束形式的数据处理方法. 对原始数据的操作不可避免地破坏了原始数据的完整性. 现今, 正电子发射断层设备在重建过程中普遍采用平行束重建的方法. 平行束的数据分离会对PET数据进行插值操作, 扇形束的数据分离不会对PET数据进行插值操作. 本文通过对比平行束图像重建和扇形束图像重建结果, 研究了数据插值对PET图像重建结果的影响. 关键词： 正电子发射计算机断层扫描 数据插值 图像重建 原始数据     

正电子显微镜

用正电子代替电子作为人射束流可组成新的显微镜．正电子从固体表面的重发射受表面和表面层下空位型缺陷的影响，因此正电子显微镜可用于无损探测扣研究表面层下的缺陷．     

射线技术在医学领域的应用

正照片说明:图1用于肿瘤放射治疗的医用加速器关键部件-加速管图2用于人体全身扫描用PET样机图3用于乳腺癌早期微小病灶筛查和良恶性诊断的国内首台技术领先的乳腺专用分子影像诊断系统图4可同时进行正电子、单光子成像的双核素多功能乳腺成像系统图5面向小型活体动物,尤其是昆虫、鱼类以及小鼠、大鼠等啮齿动物的全身或局部结构高信噪比三维能谱成     

正电子湮没发射断层照相

Robertson等人于1964年首先提出了关于正电子湮没发射断层照相问题.近十年来,由于这方面的研究工作深入开展,同时有一大批中、小型回旋加速器用于应用物理的研究,能方便地生产应用放射性同位素,所以正电子湮没发射断层照相得到了明显的发展. 一、基本原理 介质中的高能正电子与     

BEPCⅡ正电子源磁通压缩装置的研制

正电子磁通压缩装置(Flux Concentrator，简称磁号)是正电子束流横向发射度的匹配装置，对提高正电子的俘获效率起非常关键的作用，是BEPCII正电子源的重要组成部分. 结合磁号的设计加工，用计算机软件模拟了磁号的磁场分布和共振特性，并同测量结果进行了比较.     

正电子医学成像

 自从1932年发现正电子以来,已经有70个年头了。从上世纪50年代初开始研究正电子医学成像以来,经过半个世纪的历程,目前正电子医学成像技术已发展成为现代医学影像技术的独具特色的重要组成部分,在医学临床诊断和对生命科学的研究方面发挥着重要作用。一、正电子与正电子放射性核素英国理论物理学家狄拉克于1928年从理论上预言了自然界中应当存在着反电子。这种反电子具有与普通电子(负电子)一样的静止质量和相等数量的电荷。所不同的是它所带的是正电荷,因此把这种反电子称为正电子。     

用超声鉴别生物组织的特性——(Ⅰ)

一酬吉 、、声..-」 件:厂”物理学原理和电子学技术相结合,用之于乒学,大大扩展了现代医学的诊断手段和能力.上个世纪末x射线的发现,使透视人体内部器官,特别是骨组织乡第一次成为可能;到了本世纪四十年代,超声诊断开始用于临床,并且在七十到八十年代间得以迅猛的发展;近些年出现的核磁共振成像,又一次为医学诊断打开了一个新局面二’‘ 在现有的医学成像系统中,超声成像是比较独特的、「x射线,‘射线、正电子及核磁共振等成像系统使用的都是电磁波,而超声成像所用的是机械波;放射性成像(包括x射线、1射线等)表现的是组织的某种吸收性质,核…     

Selection of optical radiation in scattering in partially ordered disperse media

Results of theoretical studies of the interaction between optical radiation and partially ordered disperse media are reported. In terms of the amplitude-phase screen model consideration is given to the concentration effects of whitening and darkening in random close-packed systems of optically soft particles. The concentration dependence of transmission of close-packed systems of coarse particles is described with the use of a small-angle solution of the stochastic finite-difference transfer equation. The effects of coherent reirradiation occurring in close-packed monolayers of highly refracting particles are analyzed using a quasicrystalline approximation of the theory of multiple wave scattering and the radial particle distribution function obtained from a solution of the Percus-Yevick equation. This approach extended to multilayer systems is used to describe formation of forbidden photon zones in transmission spectra of one- and three-dimensional disperse systems with a high degree of ordering. Results of quantitative calculations are shown to agree well with experimental data. The possibility of using established regularities for optimization of spectral characteristics of selective elements based on spatially ordered disperse systems with different structural organization is discussed. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 721–733, September–October, 1998.     

ADBD plasma surface treatment of PES fabric sheets

Plasma treatment of textile fabrics is investigated as an alternative to the environmentally hazardous wet chemical fabric treatment and pretreatment processes. Plasma treatment usually results in modification of the uppermost atomic layers of a material surface and leaves the bulk characteristics unaffected. It may result in desirable surface modifications, e.g. surface etching, surface activation, cross-linking, chain scission and oxidation. Presented paper contains results of the applicability study of the atmospheric pressure dielectric discharge (ADBD), i.e. dielectric barrier discharge sustaining in air at atmospheric pressure and ambient temperature for synchronous treatment of several sheets of fabric. For tests sheets of polyester fabric were used. Effectivity of the modification process was determined with hydrophilicity measurements evaluated by means of the drop test. Hydrophilicity of individual sheets of fabric has distinctly increased after plasma treatment. Plasma induced surface changes of textiles were also proven by identification of new functional groups at the modified polyester fabric surface. Existence of new functional groups was detected by ESCA scans. For verification of surface changes we also applied high-resolution microphotography. It has shown distinct variation of the textile surface after plasma treatment. Important aspect for practical application of the plasma treatment is the modification effect time-stability, i.e. time stability of acquired surface changes of the fabric. The recovery of hydrophobicity was fastest in first days after treatment, later gradually diminished until reached almost original untreated state.     

Fluorescence of free complex molecules

A number of phenomena that determine the nature of the fluorescence of free complex molecules and the possibility of its analytical application are considered. Attention is specially paid to the specific features of the energetics of radiationless transitions, the role of statistical factors in the formation of spectral properties and the interrelationship among the luminescence-spectrum characteristics of rarefied vapors of complicated molecules, and the processes of energy transfer in collisions. The properties of polarized fluorescence of hot and jet-cooled vapors, the processes of relaxation of anisotropy in time and during collision reorientation, and transfer of anisotropy in photodisintegration are analyzed. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 620–634, September–October, 1998.     

Effects of linear absorption on the steady-state behavior of a photorefractive phase-conjugate mirror

A photorefractive phase-conjugate mirror with linear absorption is examined. An objective of this study is to identify possible effects of absorption on the self-oscillation conditions of the mirror and the properties of the excited conjugate wave. It has been found that self-oscillation is still possible in the presence of absorption. However, the coupling coefficient required for self-oscillation must increase in magnitude with increasing absorption coefficient to counteract the depressing effects of absorption. A consequence of self-oscillation in the presence of absorption is enhancement of the mirror reflectivity. A parametric study of the absorption-enhanced mirror is presented.The authors wish to acknowledge the contributions of Dai Sieh during the initial phase of this study. The work that he completed as part of his Master of Science thesis was an important element in our study of PCM reflectivity enhancement. The authors also acknowledge the assistance of Sahaid Rauf in carrying out some of the numerical solutions of Eq. 10, the governing equation of the self-oscillatory modes.     

On classification and special features of motion of dynamic systems

A number of debatable problems of modern nonlinear physics are discussed. A classification of deterministic systems with chaotic behavior by the degree of openness and type of motion is suggested. Examples of dynamic systems illustrating the consistency of this classification are presented, and special features of functioning of these systems and problems of quantitative estimation of the degree of randomness are considered. A strict definition of quasi-deterministic chaos is given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 49–58, November, 2006.     

Representations of Lie algebras and the problem of noncommutative integrability of linear differential equations

An algorithm is proposed for integrating linear partial differential equations with the help of a special set of noncommuting linear differential operators — an analogue of the method of noncommutative integration of finite-dimensional Hamiltonian systems. The algorithm allows one to construct a parametric family of solutions of an equation satisfying the requirement of completeness. The case is considered when the noncommutative set of operators form a Lie algebra. An essential element of the algorithm is the representation of this algebra by linear differential operators in the space of parameters. A connection is indicated of the given method with the method of separation of variables, and also with problems of the theory of representations of Lie algebras. Let us emphasize that on the whole the proposed algorithm differs from the method of separation of variables, in which sets of commuting symmetry operators are used.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 95–100, April, 1991.     

Modern aspects of plastic deformation in metals

After a historical survey of crystal plasticity the rôle of dislocations in plastic deformation of metals is outlined. The theory of plastic deformation in metal single crystals before the impact of transmission electron microscopy is described. Recent experimental results on glide and workhardening in single crystals of b.c.c. metals are reviewed and explained by a simple dissociation model of the screw-dislocation cores. A relative success of this explanation together with calculations of atomic structure of dislocation cores support the conclusion that different structures of screw dislocation cores are responsible for both differences and similarities between plastic behaviour of f.c.c. and b.c.c. metals. Further developments in the field of metal crystal plasticity by modern experimental techniques (transmission electron microscopy of deformed crystals in the stress-applied state, magnetic studies of dislocations in ferromagnetic crystals) and by atomic calculations of defect configurations are discussed.Na Slovance 2, Praha 8, Czechoslovakia.Invited paper presented on a plenary session of the First European Conference on the Physics of Condensed Matter organized by the Board of the Condensed Matter Division of E.P.S., in Florence on 14–17 September 1971 (Chairman: Prof. S. F. Edwards; Schuster Laboratory, University of Manchester).     

Interval of equilibrium for the logarithmic potential of an extremal measure with a constraint, and the continuum limit of the Toda lattice

The equilibrium set, in the form of an interval on the real line, of the potential of an extremal measure for some energy minimization problem is studied for the energy functional with the logarithmic kernel provided that the external field exists. The minimum of the functional is sought on a set of measures bounded by a given measure. In particular, we prove that, under a special dependence of the external field on time, the ends of the interval of equilibrium satisfy a system of partial differential equations, the so-called continuum limit of the Toda lattice. Another result of the paper is a system of integral equations for the ends of the interval of equilibrium. Dedicated to the memory of B. M. Levitan Supported by RFBR grants nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy of Sciences, and by INTAS project no. 03-51-6637.     

Mössbauer study of the separation of the rf sideband and collapse effects in invar

This report describes an investigation of the influence of coating of invar foil with various materials on the sideband and collapse effects caused by an applied r.f. magnetic field. It is shown that coating of invar foil with nonmetallic materials causes a decrease of the r.f. sideband effect without affecting the r.f. collapse effect. Coating with metallic materials reduces both r.f. effects because of screening due to the r.f. field. The separation of the r.f. sideband and collapse effects due to coating allows us to distinguish the different origins of these effects, and suggests that the r.f. sidebands are of magneto-acoustic origin, while the r.f. collapse is of purely magnetic origin.     

Broadening and collisional interference of lines in the IR spectra of ammonia. Theory

The general theory of relaxation spectral shape parameters in the impact approximation (M. R. Cherkasov, J. Quant. Spectrosc. Radiat. Transfer 141, 73 (2014)) is adapted to the case of line broadening of infrared spectra of ammonia. Specific features of line broadening of parallel and perpendicular bands are discussed. It is shown that in both cases the spectrum consists of independently broadened singlets and doublets; however, the components of doublets can be affected by collisional interference. The paper is the first part of a cycle of studies devoted to the problems of spectral line broadening of ammonia.