基于ANEP染料荧光光谱迁移的单波长心脏光学标测系统

近几年来,光学标测技术已经成为心脏电生理研究中一种非常重要的手段。它利用对嵌在细胞膜上的电压敏感染料随着膜电位变化而产生的荧光光谱迁移进行成像,来进行心律失常与电击除颤等电生理研究。文章测量了常用的电压敏感染料di-4-ANEPPS的荧光光谱,并根据该染料的光谱迁移,设计了一套包括一个通用CCD相机的单波长光学标测系统,可以达到较高的时空分辨率。记录心肌细胞中的电兴奋传导过程,从而可以为今后国内心律失常作用机制的研究工作提供一个有力的工具。     

Two models of anisotropic propagation of a cardiac excitation wave

Propagation of the action potential in the real heart is direction-dependent (anisotropic). We propose two general physical models explaining this anisotropy on the cellular level. The first, “delay” model takes into account the frequency of the cell-cell transitions in different directions of propagation, assuming each transition requires some small time interval. The second model relies on the assumption that the action potential transmits to the next cell only from the area at the pole of the previous cell. We estimated parameters of both models by doing optical mapping and fluorescent staining of cardiac cell samples grown on polymer fiber substrate. Both models gave reasonable estimations, but predicted different behaviors of the anisotropy ratio (ratio of the highest and lowest wave velocities) after addition of the suppressor of sodium channels such as lidocaine. The results of the experiment on lidocaine effect on anisotropy ratio were in favor of the first, “delay” model. Estimated average cell-cell transition delay was 240 ± 80 μs, which is close to the characteristic values of synaptic delay.     

Arrhythmogenesis in the heart: Multiscale modeling of the effects of defibrillation shocks and the role of electrophysiological heterogeneity

The mechanisms of initiation of ventricular arrhythmias as well as those behind the complex spatiotemporal wave dynamics and its filament organization during ventricular fibrillation (VF) are the topic of intense research and debate. Mechanistic inquiry into the various mechanisms that lead to arrhythmia initiation and VF maintenance is hampered by the inability of current experimental techniques to resolve, with sufficient accuracy, electrical behavior confined to the depth of the ventricles. The objective of this article is to demonstrate that realistic 3D simulations of electrical activity in the heart are capable of bringing a new level of understanding of the mechanisms that underlie arrhythmia initiation and subsequent organization. The article does this by presenting the results of two multiscale simulation studies of ventricular electrical behavior. The first study aims to uncover the mechanisms responsible for rendering the ventricles vulnerable to electric shocks during a specific interval of time, the vulnerable window. The second study focuses on elucidating the role of electrophysiological heterogeneity, and specifically, differences in action potential duration in various ventricular structures, in VF organization. Both studies share common multiscale modeling approaches and analysis, including characterization of scroll-wave filament dynamics.     

An investigation into the role of the optical detection set-up in the recording of cardiac optical mapping signals: A Monte Carlo simulation study

Photon scattering is known to distort the fluorescence signals recorded from optically mapped cardiac tissue. However, the contribution of the parameters which define the optical detection set-up has not been assessed. In this study, Monte Carlo (MC) simulations of photon scattering within ventricular tissue are combined with a detailed model of a tandem-lens optical detection apparatus to characterise (i) the spatial origin upon emission of photons recorded in voltage-sensitive fluorescence measurements of cardiac electrical activity (using the fluorescent dye di-4-ANEPPS) and how this affects signal distortion, and (ii) the role the detector characteristics could play in modulating signal distortion during uniform illumination and photon emission from tissue depth. Results show that, for the particular excitation/emission wavelengths considered (488 nm and 669 nm, respectively), the dimensions of the scattering volume during uniform illumination extend around 3 times further in the surface recording plane than in depth. As a result, fluorescence recordings during electrical propagation are more distorted when transmembrane potential levels differ predominantly in the surface plane than in depth. In addition, MC simulation results show that the spatial accuracy of the fluorescence signal is significantly limited due to photon scattering, with only a small fraction of the recorded signal intensity originating from tissue beneath the pixel (approximately 11% for a 0.25×0.25 mm pixel). Increasing pixel size increases this fraction, however, it also results in an increase in the scattering volume dimensions, thus reducing the spatial resolution of the optical system, and increasing signal distortion. MC simulations also demonstrate that photon scattering in cardiac tissue limits the ability of optical detection system tuning in accurately locating fluorescent emission from depth. Specifically, our results prove that the focal plane depth that yields maximum signal intensity provides an underestimation of the emission depth. In conclusion, our study demonstrates the potential of MC simulations of photon scattering in guiding the design of optical mapping set-ups to optimise performance under diverse experimental conditions.     

岩心显微拉曼光谱成像方法的研究

虽然用激光拉曼光谱显微探针研究岩心中碳质物的工作已有很大进展,但是通常对诸如岩心等样品物性的光谱学(红外、拉曼和荧光等)微探针实验研究多是局限于对经过复杂处理分离出的微小样品或样品中个别点得到的结果,缺乏对复杂样品各组分(或基团)的空间分布及其相互关系的研究。近年来新发展起来的光谱成像分析系统将光谱技术与成像技术有机地结合起来融为一体,可在光谱和空间两个方面对目标样品进行分析和识别,但是用拉曼显微成像光谱研究岩心的工作则少有报道。文章报道了应用“串行-成像”(series-or indirect-imaging,Mapping)和“并行-成像”(parallel-or direct-imaging, Imaging)两种方式对含油岩心进行了显微拉曼光谱成像的研究。从光谱分辨率和空间分辨率以及工作效率等方面对两种方式所得试验结果进行了比较和评估。     

Complete dynamical analysis of myocardial cell exposed to magnetic flux

The heart is the essential, yet complex, component of the human cardiovascular system. In the past few decades, researchers have taken giant steps toward better understanding of the cardiac system and there have been proposed some mathematical models to describe the heart's function. In this paper, a new Fitzhugh-Nagumo neuron (FNN) model is proposed to model the electrical activity of the heart in which the effect of magnetic flux is considered. Magnetic field can greatly affect the heart's function. The dynamical analyses of the model, including quantitative assessment of the system's equilibria and its stability, phase portraits analysis, bifurcation and Lyapunov exponents analysis, and basin of attraction analysis, are carried out. In addition, a model of cardiac tissue is designed to study the electrical spatiotemporal activity of heart tissue under the electromagnetic effects. Our numerical simulations confirm that the electromagnetic excitation can change the normal rhythm of the heart. It can initiate the reentrant excitations leading to emergence of spiral seeds. This study highlights the role of electromagnetic induction in dynamical instability of the action potential duration, and thus the chaotic dynamics in the cardiac tissue.     

Modeling wave propagation in realistic heart geometries using the phase-field method

We present a novel algorithm for modeling electrical wave propagation in anatomical models of the heart. The algorithm uses a phase-field approach that represents the boundaries between the heart muscle and the surrounding medium as a spatially diffuse interface of finite thickness. The chief advantage of this method is to automatically handle the boundary conditions of the voltage in complex geometries without the need to track the location of these boundaries explicitly. The algorithm is shown to converge accurately in nontrivial test geometries with no-flux (zero normal current) boundary conditions as the width of the diffuse interface becomes small compared to the width of the cardiac action potential wavefront. Moreover, the method is illustrated for anatomically realistic models of isolated rabbit and canine ventricles as well as human atria.     

Direct detection of neuronal activity with MRI: Fantasy, possibility, or reality?

Hemodynamic-based functional magnetic resonance imaging (fMRI) techniques have proven to be extremely robust and sensitive methods for noninvasive detection and mapping of human brain activation. Nevertheless, limitations in temporal and spatial resolution as well as interpretation remain because hemodynamic changes accompanying brain activation are relatively sluggish and variable and therefore imprecise measures of neuronal activity. A hope among brain imagers would be to possess a technique that would allow direct mapping of brain activity with spatial resolution on the order of a cortical column and temporal resolution on the order of an action potential or at least a postsynaptic potential. Recent efforts in understanding the direct effects of neuronal activity on MRI signal have provided some degree of hope for those who want a more precise noninvasive brain activation mapping technique than fMRI as we know it now. While the manner in which electrical currents influence MRI signal is well understood, the manner in which neuronal firing spatially and temporally integrates on the spatial scale of an MRI voxel to produce a magnetic field shift and subsequently an NMR phase and/or magnitude change is not well understood. It is also not established that this field shift would be large or long enough in duration to be detected. The objective of this paper is to provide a perspective of the work that has been performed towards the direction of achieving direct neuronal current imaging with MRI. A specific goal is to further clarify what is understood about the theoretical and practical possibilities of neuronal current imaging. Specifically discussed are modeling efforts, phantom studies, in vitro studies, and human studies.     

Imaging the Hydrated Microbe‐Metal Interface Using Nanoscale Spectrum Imaging

PdAu nanocrystals are synthesised by Geobacter sulfurreducens, a dissimilatory metal‐reducing bacterium, and the resulting bimetallic nanocrystal‐decorated microbes are imaged using a range of advanced electron microscopy techniques. Specifically, the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X‐ray (EDX) spectrum imaging within an environmental liquid‐cell is reported. These results are combined with cryo‐TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. It is demonstrated that although Au and Pd are colocalized across the cells, the population of nanoparticles produced is bimodal, containing ultrasmall alloyed nanocrystals with diameters <3 nm and significantly larger core‐shell structures (>200 nm in diameter) which show higher Pd contents and exhibit a Pd enriched shell only a few nanometers thick. The application of high‐resolution imaging techniques described here offers the potential to visualize the microbe‐metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g., metal cycling).     

基于心脏腔式结构的心电图元胞自动机建模

建立了包含心房肌、心室肌、房室腔、室间隔并考虑心室肌分层结构的心电图元胞自动机模型.利用所建立的模型,仿真了电信号在心脏中的传导,计算了正常和缺血情况下的场点电势走势.数值结果表明:正常情况下,模拟所得的场点电势呈现与标准心电图一致的P波、QRS波群、T波和J波;在心内膜下肌细胞缺血情况下,出现T波倒置的现象;在心外膜下肌细胞缺血情况下,T波变得高耸;在透壁缺血情况下,T波提前形成,QT间期缩短.将正常和异常情况下的场点电势走势与临床结果进行了对比,并分析了其形成与持续机制.研究结果可为准确阐明心电图与心肌细胞电活动之间的关系、探讨心电图的产生与持续机制提供参考.     

Study of electrical field distribution of gold-capped nanoparticle for excitation of localized surface plasmon resonance

The specific optical characteristics which can be observed from noble metal nanostructured materials such as nanoparticles and nanoislands have wide variety of applications such as biosensors, solar cells, and optical circuit. Because, these noble metal nanostructures induce the increment of light absorption efficiency by the enhancing effect of electrical field from localized surface plasmon resonance (LSPR) excitation. However, the enhancing effects of electrical field from LSPR using simple structured noble metal nanostructures for several applications are not satisfactory. To realize the more effective light absorption efficiency by the enhancing effect of electrical field, quite different noble metal nanostructures have been desired for applying to several applications using LSPR. In this study, to obtain the more effective enhancing effect of electrical field, conditions for LSPR excitation using a gold-capped nanoparticle layer substrate are computationally analyzed using finite-difference time-domain (FDTD) method. From the previous research, LSPR excitation using such gold-capped nanoparticle layer substrates has a great potential for application to high-sensitive label-free monitoring of biomolecular interactions. For understanding of detailed LSPR excitation mechanism, LSPR excitation conditions were investigated by analyzing the electrical field distribution using simulation software and comparing the results obtained with experimental results. As a result of computational analysis, LSPR excitation was found to depend on the particle alignment, interparticle distance, and excitation wavelength. Furthermore, the LSPR optical characteristics obtained from the simulation analysis were consistent with experimentally approximated LSPR optical characteristics. Using this gold-capped nanoparticle layer substrate, LSPR can be excited easily more than conventional noble metal nanoparticle-based LSPR excitation without noble metal nanoparticle synthesis. Hence, this structure is detectable a small change of refractive index such as biomolecular interactions for biosensing applications.     

Digital photocontrol of the network of live excitable cells

Recent development of tissue engineering techniques allows creating and maintaining almost indefinitely networks of excitable cells with desired architecture. We coupled the network of live excitable cardiac cells with a common computer by sensitizing them to light, projecting a light pattern on the layer of cells, and monitoring excitation with the aid of fluorescent probes (optical mapping). As a sensitizing substance we used azobenzene trimethylammonium bromide (AzoTAB). This substance undergoes cis-trans-photoisomerization and trans-isomer of AzoTAB inhibits excitation in the cardiac cells, while cis-isomer does not. AzoTAB-mediated sensitization allows, thus, reversible and dynamic control of the excitation waves through the entire cardiomyocyte network either uniformly, or in a preferred spatial pattern. Technically, it was achieved by coupling a common digital projector with a macroview microscope and using computer graphic software for creating the projected pattern of conducting pathways. This approach allows real time interactive photocontrol of the heart tissue.     

A “three colour channel” system to synthesize complex point spread functions

In this paper a “hybrid” system is introduced, which consists of an incoherent optical system and an electronic system, In the optical processor the temporal as well as the spatial frequencies of the input image are manipulated. A CTV camera transposes the light distribution at the output of the optical system into three electrical signals. These electrical signals are modulated and combined to one signal, which will be fed into a visual display, showing a fringe pattern, whose brightness is proportional to the magnitude of the desired (complex) image.     

Defibrillation via the elimination of spiral turbulence in a model for ventricular fibrillation

Ventricular fibrillation, the major reason behind sudden cardiac death, is turbulent cardiac electrical activity in which rapid, irregular disturbances in the spatiotemporal electrical activation of the heart make it incapable of any concerted pumping action. Methods of controlling ventricular fibrillation include electrical defibrillation as well as injected medication. Electrical defibrillation, though widely used, involves subjecting the whole heart to massive, and often counterproductive, electrical shocks. We propose a defibrillation method that uses a very low-amplitude shock (of order mV) applied for a brief duration (of order 100 ms) and over a coarse mesh of lines on our model ventricle.     

Optical Properties of Metal-Dielectric Structures Based on Photon-Crystal Opal Matrices

Optical properties of novel metal–dielectric nanocomposite materials based on opal matrices have been investigated. The position of optical resonances of nanocomposites, obtained by embedding of silver into the opal matrix by the electrothermodiffusion method, is explained by the Bragg diffraction, and an asymmetric form of resonance curves is attributed to the Fano resonance. An anomalous transmission and absorption of light by hybrid plasmon-photonic layered heterostructures, which is apparently associated with excitation of surface plasmon-polaritons, propagating along “metal–dielectric” interfaces, was revealed.

     

(2+1)维非对称 Nizhnik-Novikov-Veselov系统的新映射解及其局域结构

映射法是一种非常经典、有效和成熟的求解非线性演化方程的方法，其最大的特点是可以有多种不同形式的设解，使得最终求得的解丰富多彩. 利用改进的 Riccati 方程映射法和变量分离法，得到了(2+1)维非对称 Nizhnik-Novikov-Veselov 系统的新显式精确解.根据得到的孤波解，构造出该系统的峰孤子和分形孤子等局域结构，研究了两个孤立波的“追碰”现象. 关键词： 改进的映射法 (2+1)维非对称 Nizhnik-Novikov-Veselov 系统 局域结构 “追碰”现象     

Introduction: Mapping and control of complex cardiac arrhythmias

This paper serves as an introduction to the Focus Issue on mapping and control of complex cardiac arrhythmias. We first introduce basic concepts of cardiac electrophysiology and describe the main clinical methods being used to treat arrhythmia. We then provide a brief summary of the main themes contained in the articles in this Focus Issue. In recent years there have been important advances in the ability to map the spread of excitation in intact hearts and in laboratory settings. This work has been combined with simulations that use increasingly realistic geometry and physiology. Waves of excitation and contraction in the heart do not always propagate with constant velocity but are often subject to instabilities that may lead to fluctuations in velocity and cycle time. Such instabilities are often treated best in the context of simple one- or two-dimensional geometries. An understanding of the mechanisms of propagation and wave stability is leading to the implementation of different stimulation protocols in an effort to modify or eliminate abnormal rhythms. (c) 2002 American Institute of Physics.     

极紫外光学器件辐照污染检测技术

总结并讨论了极紫外光刻技术中,有关极紫外光学器件受辐照污染的"在线"检测方法。简要介绍了极紫外光刻系统的原理、反射镜膜层结构以及表面污染产生的机理;指出光刻系统中"在线"检测的技术要求;分析了目前几种主要表面检测技术的特点;给出了每种方法在极紫外光学系统中的应用潜力;最后,指出光纤椭偏仪在极紫外光学系统的"在线"表面污染检测中具有良好的应用前景。     

多腔体心脏磁场模型的研究与应用

利用核磁共振图像(MRI)中提取的人体和心脏边界,根据边界元方法(BEM)建立了一个考虑左、右心房和心室的多腔体心脏磁场模型.分析了用该模型得到的36通道心脏磁场数据和特定时刻的磁场图.并在此基础上,研究了完全性右束支传导阻滞(CRBBB)和完全性左束支传导阻滞(CLBBB)病人ST-T段的心脏电活动.结果显示,用移动单电流偶极子模拟的单束支电兴奋传导所产生的磁场图与用超导量子干涉器(SQUID)测量的CRBBB/CLBBB病人数据绘制的心脏复极时的心磁图(MCG)十分相似.结果表明,该多腔体心脏BEM模型可用于CLBBB/CRBBB病人心脏磁场逆问题的研究.此外,文中给出了两个评价指标:测量平面上多腔体与单腔体的心脏磁场强度极大值之比,以及两种模型的36个测量点上磁场强度均方根之比.分析表明,多腔体心脏模型更贴近人体心脏的实际情况.该模型中心脏组织电导率参数的取值,以及等效电流偶极子的位置和个数决定了磁场的强度和分布.