Reconstruction of the blood flow pattern by tomography of the acoustic nonlinearity parameter: Computer simulation and physical experiment

A method is proposed for reconstructing the distribution of the total blood flow velocity vector from the data obtained within the nonlinear parameter tomography scheme. The method calculates the Doppler shift of the combination frequency with the use of the spectral analysis of the combination signal and the moving target selection procedure. Results of numerical simulations are presented, and possibilities of practical application of the method are discussed. A physical experiment is carried out. The results of this experiment are found to be in good agreement with the theory and the numerical model.     

A spatial correlation method for reconstructing blood flow velocity vector in the nonlinear tomography

A method for reconstructing the total blood flow velocity vector distribution is proposed. Experimental data are obtained with the help of the second-order nonlinearity parameter tomography scheme that employs wideband coded signals and a small number of transducers. The data are processed using the selective matched filtering technique in combination with spatial correlation of fragments of the speckle structure that appears in the process of reconstruction of the spatial nonlinearity parameter distribution. Results of numerical simulations are presented.     

Reconstruction of the acoustic impedance profile in a plate using an inverse spectral procedure

An inverse spectral procedure was applied to reconstruct the acoustic impedance profile along the thickness direction of a plate using its thickness resonance frequencies, density and thickness. For a successful reconstruction, the material-property profile must be symmetric about the mid-plane of the plate. Several cases of numerical simulations, including plates with a few layers and with a high number of layers are described. The calculated resonance frequencies were used to reconstruct the acoustic impedance profile, a process that was successful for all cases. We assume that a plate with a high number of layers, each with a different but constant acoustic impedance, simulates a plate with a smoothly varying acoustic impedance profile. It can be concluded that such a plate, which generates small, virtually undetectable, internally reflected waves, can also be reconstructed. In the special case of a plate of unknown thickness and unknown but constant density, the method is still useful, because a relative variation of the material property can be reconstructed using only the resonance frequencies. An experiment using a resonance-mode electromagnetic acoustic transducer (resonance-mode EMAT) is also described. EMAT is a non-contact ultrasonic method that can measure thickness resonance frequencies, making it appropriate for this method. Some examples of applications are measurement of the temperature profile inside a rolled metal sheet, measurement of a clad metal plate, and monitoring of a metal casting.     

Measurement of velocity distribution for longitudinal acoustic waves in welds by a laser optoacoustic technique

An optoacoustic technique for diagnostics of residual stress in metals is proposed. The theoretical part of the technique employs acoustoelastic relations establishing a linear relationship between the biaxial residual stress and the relative variation of the velocity of longitudinal ultrasonic waves. The experimental technique is based on laser excitation of nanosecond ultrasonic pulses at the surface of samples under investigation and their detection with a high time resolution. Distributions of the relative variation of longitudinal wave velocities due to the presence of residual stress in the samples are obtained.     

Reconstruction of the blood flow velocity vector as an additional mode of ultrasonic tomograph

The possibility of simultaneous reconstruction of the blood flow velocity vector and spatial distributions of the speed of sound and absorption coefficient in a medical ultrasonic tomograph is discussed. The operating capacity of the proposed spatial-correlation method for determining the blood flow velocity vector is confirmed by experiments on a tomograph prototype.     

Quantification of a three-dimensional velocity vector using spectral-domain Doppler optical coherence tomography

Multiangle, fiber-based, spectral-domain Doppler optical coherence tomography with a phase-resolved algorithm is presented to measure three components of an arbitrary velocity vector. A beam divider that divides a probe beam to have five independent viewpoints and path length delays was designed. The divider was inserted into the sampling arm of a Doppler optical coherence tomography system between the collimator and the first galvo mirror of a two-axis galvo scanner. The divider produced five independent D k's (the average difference between the wave vectors of incoming and outgoing beams) after passing through the focusing lens while keeping two-axis scanning capability. After calibration, an unknown velocity vector field inside a microtube was quantified by solving a three-dimensional minimization problem.     

基于矢量水听器的声压和质点振速的空间相关系数

矢量水听器同步测量声场空间一点处的声压和质点振速的三个正交分量,由此得到的幅度和相位信息有利于改善声呐的检测和估计性能。对三维球形各向同性噪声场中声压和质点振速的时空相关性本文进行了研究,推导了矢量水听器的噪声协方差矩阵的理论表达式;给出了矢量水听器水平线阵和垂直线阵的协方差矩阵;研究单个矢量水听器的噪声协方差矩阵,并给出了浅海近岸水域的试验结果;利用上述理论结果推导了矢量水听器阵列的声能流阵增益。     

Transient acoustic holography for reconstructing the particle velocity of the surface of an acoustic transducer

A transient acoustic holography method based on the Rayleigh integral and the time-reversal mirror principle is described. The method reconstructs the particle velocity of the surface of an acoustic source from the waveform of the signal measured over a surface lying in front of the source. The possibility of applying the transient holography to studying pulsed sources used in ultrasonic diagnostics is investigated. A rectangular source that produces a short acoustic pulse and has a nonradiating defect on its surface is considered. A numerical simulation is used to demonstrate the possibility of a holographic reconstruction of the source vibrations. The effects of the spatial sampling step and the size of the measurement region on the reconstruction quality are demonstrated.     

Measurement of absolute flow velocity vector using dual-angle, delay-encoded Doppler optical coherence tomography

Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.     

声矢量阵指向性

单矢量传感器具有可电子旋转的偶极子指向性,声压、振速信息联合矢量信号处理在噪声背景下有良好的探测能力,矢量(传感器)阵能取得更好的能力。本文对理想条件下单矢量传感器、二元矢量阵的偶极子指向性和单边指向性进行了计算机仿真,并对单矢量传感器的指向性进行了水池实验,实验结果与仿真结果基本一致。结果表明矢量传感器具有较强的抗相干干扰和非相干干扰的能力。     

Image reconstruction in optoacoustic tomography for dispersive acoustic media

Conventional image reconstruction methods for optoacoustic tomography (OAT) assume an idealized, non-dispersive acoustic medium. However, the linear attenuation coefficient and the phase velocity of acoustic waves propagating in soft tissue depend on temporal frequency and satisfy a known dispersion law. These frequency-dependent effects are incorporated into an optoacoustic wave equation, and a corresponding reconstruction method for OAT is developed. The improvement in image fidelity that can be achieved over conventional reconstruction methods is demonstrated by use of computer-simulation studies.     

Fiber-optic tomography of acoustic fields

Institute of Applied Physics, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 11, pp. 1388–1393, November, 1988.     

Direction-of-arrival estimation for extensible acoustic vector sensor array

Aiming at high-resolution estimation of the direction-of-arrival of closely-spaced sources at low signal-to-noise ratio regions, this paper proposes a DOA estimation algorithm that is suitable for an extensible acoustic vector sensor array. Taking the 3D array composed of the minimum number(four) of acoustic vector sensors as the acquisition module, a virtual array having the same structure as the original array structure is extended in the three-dimensional space based on the aperture expansion...     

Determination of flow velocity vector based on Doppler shift and spectrum broadening with optical coherence tomography

We describe a technique that uses Doppler optical coherence tomography to estimate accurately the scattering fluid-flow velocity without a priori knowledge of the Doppler angle. Our technique is based on the combined use of the Doppler shift on the interference signal and the Doppler spectrum broadening caused by the particles moving across the probe beam. It is shown that the estimated values of the Doppler angle and average fluid velocity from the experiments agree well with the preset values.     

声速测量实验装置扩展应用

通过对声速测量装置进行适当的改进,使其既能测量空气中的声速,也能测量水、甘油等液体中的声速,减少重复购置仪器的投资,提高了仪器的利用率.     

The study of underwater acoustic communication technology based-on the acoustic vector sensor

Underwater acoustic (UWA) communication based on an acoustic vector sensor is studied. The method of joint weighted sound pressure and velocity processing is used in phase modulation high-speed UWA communication system combined with coherent demodulation and adaptive equalization algorithm to demodulate and decode. Whereas the sound intensity could be used instead of pressure for frequency decoding in frequency modulation UWA communication system. The results of theory analysis, simulation calculations and lake trials have shown that either in phase modulation or in frequency modulation UWA communication system, the processing gain can be evidently increased, so that the BER (bit error rate) can be effectively reduced and the telemetry distance can be enlarged by using the acoustic vector sensor.     

基于声矢量传感器的水声通信技术研究

基于声矢量传感器声压和振速联合加权处理可以提高空间处理增益的原理,将声矢量传感器应用于相位调制的高速水声通信中,并结合自适应均衡算法,研究了相干解调和解码的方法。基于声矢量传感器声强处理可以抵消各向同性干扰、提高信噪比的原理,研究了在频率调制的水声通信系统中,利用声强解码代替声压解码的方法。理论分析、仿真研究和湖上试验结果表明:利用声矢量传感器相对于声压传感器来说,可以提高解码处理增益,进而提高了水声通信系统的作用距离、降低误码率。     

Causality and the velocity of acoustic signals in bubbly liquids

Several versions of the dispersion formula governing the acoustic propagation in bubbly liquids are shown to exhibit acausal behavior. The cause of this behavior is due to the inappropriate application of a low frequency approximation in the determination of the extinction of the signal from radiative scattering. Using a corrected causal formula, several principles of wave propagation in bubbly media consistent with the general theory of wave propagation in dispersive media are demonstrated: There exist two precursors to any finite signal. Both propagate without regard to the source characteristics at velocities, frequencies, and amplitudes dependent wholly upon the characteristics of the medium supporting the wave motion. The first travels at the infinite frequency phase velocity that is coincident with the infinite frequency limit of the group velocity. That part of a propagating wave oscillating at the source frequency arrives at a time determined by the signal velocity. Analogous to the well known signal velocity of electromagnetic wave propagation in conducting media, the value of the signal velocity depends on the detailed structure of the dispersion formula in the complex frequency plane.     

Chapman-Enskog velocity distribution for tracer diffusion

The Chapman-Enskog method is used to obtain an approximate velocity distribution function for tracer diffusion in dilute hard-sphere mixtures. Different ratios of the mass of the tracer to that of the excess component (including the well-known limiting cases of the Lorentz and the Rayleigh models) are considered and the corresponding diffusion coefficients are also evaluated. A comparison with the recent results of Tompson and Loyalka for both the diffusion coefficients and the distribution functions provides a perspective on the usefulness and nature of the approximate method.