The effect of blood acceleration on the ultrasound power Doppler spectrum

The purpose of the present work was to study the influence of blood acceleration and time window length on the power Doppler spectrum for Gaussian ultrasound beams. The work has been carried out on the basis of continuum model of the ultrasound scattering from inhomogeneities in fluid flow. Correlation function of fluctuations has been considered for uniformly accelerated scatterers, and the resulting power Doppler spectra have been calculated. It is shown that within the initial phase of systole uniformly accelerated slow blood flow in pulmonary artery and aorta tends to make the correlation function about 4.89 and 7.83 times wider, respectively, than the sensitivity function of typical probing system. Given peak flow velocities, the sensitivity function becomes, vice versa, about 4.34 and 3.84 times wider, respectively, then the correlation function. In these limiting cases, the resulting spectra can be considered as Gaussian. The optimal time window duration decreases with increasing acceleration of blood flow and equals to 11.62 and 7.54 ms for pulmonary artery and aorta, respectively. The width of the resulting power Doppler spectrum is shown to be defined mostly by the wave vector of the incident field, the duration of signal and the acceleration of scatterers in the case of low flow velocities. In the opposite case geometrical properties of probing field and the average velocity itself are more essential. In the sense of signal–noise ratio, the optimal duration of time window can be found. Abovementioned results may contribute to the improved techniques of Doppler ultrasound diagnostics of cardiovascular system.     

Speckle interferometry and Doppler diagnostics of microflows of scattering liquids

A relation for the correlation function of intensity fluctuations of the speckle field formed upon scattering of focused light radiation in blood flows in microvessels is obtained. The width of the intensity-fluctuation spectrum is shown to depend not only on the velocity of the flow, but also on its scattering characteristics. Simulation of the processes of scattering of light beams in random flows is performed by the Monte Carlo method. The expression for the first spectral moment of the Doppler signal is derived both on the basis of the theory of radiative-energy transfer and within the framework of the speckle-interference approach; comparison of the obtained results is carried out.     

动态光散射中的多普勒效应

动态光散射中的多普勒效应郭凤岐１）刘秋霞２）（武汉工业大学数理系材料学院武汉４３００７０）ＤｏｐｐｌｅｒＥｆｅｃｔｉｎＤｙｎａｍｉｃＬｉｇｈｔＳｃａｔｅｒｉｎｇＧｕｏＦｅｎｇｑｉ，ＬｉｕＱｉｕｘｉａ（Ｄｅｐｔ．ｏｆＭａｔｈ．ａｎｄＰｈｙｓ．，Ｗｕｈａ...     

On the theory of refractive radio-wave scattering

We consider in detail the frequency correlation of radio-wave fluctuations in one or several thick layers with strong large-scale inhomogeneities of turbulent origin. General expressions are obtained for the space-frequency fluctuation correlation of the radio-waves received. We analyze particular cases of radio wave scattering in turbulent media with inhomogeneities described by power-law spectra with indices p2 and p3. It is shown, in particular, that the coherence band of signals propagated in media with strong large-scale inhomogeneities is critically dependent on the spectral type of thOse inhomogeneities. The occurrence of an additional strongly scattering layer, which has radically different properties compared to the first layer, on the radio-wave path can increase or decrease considerably the frequency correlation of the radio waves received.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 1012–1022, October, 1995.     

Microwave Doppler spectra of sea return at small incidence angles: specular point scattering contribution

It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller (≤20o). Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method (TSM) and the method of moment (MOM) are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.     

Doppler power spectrum from a Gaussian sample volume

A closed-form expression for the Doppler power spectrum due solely to the range of blood velocities passing through a Gaussian sample volume placed anywhere in a vessel under conditions of axisymmetric flow, uniform backscatter and negligible intrinsic spectral broadening has been derived. The formulation presented here allows the independent specification of the sample volume position and width, in the three dimensions, and enables simple estimations of spectral shape for pulsed wave Doppler systems. Simpler expressions were derived for the cases of symmetric sample volume projections onto the vessel cross-section and/or sample volumes centred in the vessel. Closed form expressions were derived for mean frequency and spectral width in the case of a symmetric sample volume projection centred in the vessel. The effects of sample volume size and position on the Doppler spectral width and mean frequency are shown for a range of velocity profiles.     

Tissue self-affinity and polarized light scattering in the born approximation: a new model for precancer detection

Light scattered from biological tissues can exhibit an inverse power law spectral component. We develop a model based on the Born approximation and von Karman (self-affine) spatial correlation of submicron tissue refractive index to account for this. The model is applied to light scattering spectra obtained from excised esophagi of normal and carcinogen-treated rats. Power law exponents used to fit dysplastic tissue site spectra are significantly smaller than those from normal sites, indicating that changes in tissue self-affinity can serve as a potential biomarker for precancer.     

Correlation transfer and diffusion of ultrasound-modulated multiply scattered light

We develop a temporal correlation transfer equation (CTE) and a temporal correlation diffusion equation (CDE) for ultrasound-modulated multiply scattered light. These equations can be applied to an optically scattering medium with embedded optically scattering and absorbing objects to calculate the power spectrum of light modulated by a nonuniform ultrasound field. We present an analytical solution based on the CDE and Monte Carlo simulation results for light modulated by a cylinder of ultrasound in an optically scattering slab. We further validate with experimental measurements the numerical calculations for an actual ultrasound field. The CTE and CDE are valid for moderate ultrasound pressures and on a length scale comparable with the optical transport mean-free path. These equations should be applicable to a wide spectrum of conditions for ultrasound-modulated optical tomography of soft biological tissues.     

Theoretical expressions of temporal power spectra of irradiance fluctuations for optical waves propagating through weak non-Kolmogorov turbulence

The temporal power spectra of irradiance fluctuations reflect the frequency distribution of temporal statistical property of irradiance fluctuation. In this paper, new analytical expressions of the temporal power spectral models of irradiance fluctuations are developed for optical waves propagating through weak non-Kolmogorov turbulence with horizontal path. They are derived with the general modified atmospheric spectral model, and they consider the finite turbulence inner and outer scales, and have a general spectral power law value in the range of 3 to 4 instead of the standard power law value of 11/3. Numerical calculations are conducted to analyze the influence of non-Kolmogorov weak turbulence on the temporal power spectra of irradiance fluctuations.     

Sound scattering by random fractal inhomogeneities in the ocean

Sound scattering by random volume inhomogeneities (fluctuations of the refraction index in a medium) with an arbitrary anisotropy is considered using the small perturbation method (Born’s approximation). Surfaces (boundaries) of the inhomogeneities are deemed to be fractal ones: the energy spectra of the refraction index fluctuations follow the power law with a nonintegral exponent. Formulas are obtained for the volume scattering coefficient. Frequency and angular dependences of the scattering coefficient and their relations to the fractal dimension of inhomogeneities with different kinds of anisotropy and different sizes (on the sound wavelength scale) are presented. The fractal dimension of the inhomogeneities is estimated.     

基于三维空间域移动通信统计信道的多普勒效应

针对散射体均匀分布以及三维空间域(3 dimension,3D)移动通信环境,提出了3D空间统计信道模型.对在指向性天线覆盖下的室内微小区移动通信环境,模型能够估计多径衰落信道的重要空时信道参数,如波达信号在水平面以及垂直面的信号到达角度(angle of arrival,AOA)以及多普勒效应(Doppler spectra,DS)等.移动台(mobile station,MS)的移动特性会使接收信号产生多普勒效应,根据运动的相对性理论,基站(base station,BS)也会有相对运动,因此也会有多普勒效应产生.本文引入控制变量法导出三维空间域在MS以及BS端的多普勒效应,数值仿真结果与室外3D多径衰落信道对比表明,本模型的信道参数估计结果符合理论和经验,扩展了3D空间统计信道模型的研究和应用.     

Detection of inhomogeneities in biological tissues by the methods of confocal microscopy

The model of detection of local inhomogeneities of scattering and absorbing types in biological tissues by the methods of reflection and transmission confocal microscopy has been developed on the basis of the theory of vision in scattering media. General equations for calculation of the image contrast of an inhomogeneity against the background of a scattering medium are derived. The influence of the object characteristics and observation-system parameters on the maximum detection depth of inhomogeneities is analyzed. Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 625–639, May, 1998.     

光束在强湍流区中传播的到达角起伏

 基于修正Rytov理论，导出了适用于强湍流区的无限平面波和球面波的到达角起伏方差表达式及其功率谱表达式，分析了散射盘对到达角起伏的影响。研究结果表明：导出的方差表达式在弱湍流区也适用，随着Rytov方差的增加到达角起伏趋于饱和；高频功率谱的下降速度随着散射盘尺度的增加而增加。     

Ultrasonic properties of random media under uniaxial loading.

Acoustic properties of two types of soft tissue-like media were measured as a function of compressive strain. Samples were subjected to uniaxial strains up to 40% along the axis of the transducer beam. Measurements were analyzed to test a common assumption made when using pulse-echo waveforms to track motion in soft tissues--that local properties of wave propagation and scattering are invariant under deformation. Violations of this assumption have implications for elasticity imaging procedures and could provide new opportunities for identifying the sources of backscatter in biological media such as breast parenchyma. We measured speeds of sound, attenuation coefficients, and echo spectra in compressed phantoms containing randomly positioned scatterers either stiffer or softer than the surrounding gelatin. Only the echo spectra of gel media with soft scatterers varied significantly during compression. Centroids of the echo spectra were found to be shifted to higher frequencies in proportion to the applied strain up to 10%, and increased monotonically up to 40% at a rate depending on the scatterer size. Centroid measurements were accurately modeled by assuming incoherent scattering from oblate spheroids with an eccentricity that increases with strain. While spectral shifts can be accurately modeled, recovery of lost echo coherence does not seem possible. Consequently, spectral variance during compression may ultimately limit the amount of strain that can be applied between two data fields in heterogeneous media such as lipid-filled tissues. It also appears to partially explain why strain images often produce greater echo decorrelation in tissues than in commonly used graphite-gelatin test phantoms.     

MC model of Auger spectra from highly charged ion beam surface interaction

Abstract

A Monte Carlo code is described which simulates angle resolved Auger electron energy spectra from highly charged ion surface interaction. The combined effect of the Doppler spread of laboratory emission energy and electron scattering by the solid, together with the broad inherent line width, is found to have considerable influence on the spectral lines. As a new feature, low or high energy shoulders can appear. By comparison between simulated and measured spectra information on the kinematic and electronic state of the projectile ions in the moment of electron emission can be extracted. The standard method of spectrum analysis, which is based on the assumption of direct escape of the electrons, is evaluated with respect to the simulated spectra.     

Review of fundamental processes for matter-radiation interaction

A concise review is presented of fundamental quantum electrodynamic processes which are relevant to X-ray lasers, grasers, and superpowerful lasers. Transition rates and cross sections are derived for atomic and free-electron Thomson scattering, Kramers-Heisenberg, and Raman scattering in the dipole approximation; Rayleigh scattering and C?erenkov effect. The resport includes a table of reaction rates, cross sections, stopping power, and power spectra for all processes considered.     

Mode coupling and radiation loss of clad-type optical waveguides due to the index inhomogeneities of the core material

Closed form approximate expressions are derived for the mode-coupling, radiation loss and losses of each guided mode in multimode clad-type dielectric slab waveguides due to the index inhomogeneities of the core material. The analysis considers the inhomogeneities of the core-index in the axial and transverse directions and includes correlation lengths of any magnitude. It allows us to conclude that there will be considerable mode-dependency for the mode-coupling and radiation loss if the axial and/or transverse correlation lengths are of the order of or greater than the wavelength. It is also found that the mode-coupling and radiation loss peak at some value of the axial correlation length, and the radiation loss can be reduced by increasing the refractive-index difference of the core and cladding materials. Finally, it is shown that if the correlation lengths are shorter than, or of the order of the wavelength, the losses of each guided mode will mainly be due to the radiation process. But, in the case where the axial correlation length is much greater than the wavelength, the scattering into other guided modes is the dominant mechanism.     

Stokes amplification regimes in quasi-cw pumped hydrogen-filled hollow-core photonic crystal fiber

Pure rotational stimulated Raman scattering spectra containing nine strong spectral components were generated from a approximately 11 m long hollow-core photonic crystal fiber filled with hydrogen and pumped with nanosecond pulses having energies around 100-300 nJ. Observation of both transient and steady-state scattering threshold behavior is reported. Passage from the transient to the steady state is observed with a pulse as long as 14 ns. Convenient analytical expressions for energy and power threshold are deduced for the present configuration.     

Internal tissue displacement measurement based on ultrasonic wave Doppler signal digital detection and its application to fetal movement monitoring

We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown.     

Algorithms for converting 3D surface roughness spectra when calculating frequency-angle reverberation characteristics

On the basis of an earlier developed model of sound scattering by surface disturbances characterized by 3D roughness spectra, we propose and test a sufficiently fast algorithm for calculating the spectral power density of surface reverberation that takes into account the propagation conditions, distance, and beam pattern of the receiver system. For a distance of up to 1000 m, a water area depth of ??20 m, and actually measured 3D roughness spectra in the Doppler frequency range of ±5 Hz, we have calculated the frequency-angle reverberation spectra for an acoustic background-radiation signal of 1.5 kHz. The obtained angle and frequency reverberation characteristics are compared with the results of acoustic measurements conducted using linear horizontal receiver antennas.