Target velocity estimation with FM and PW echo ranging Doppler systems I. Signal analysis

The theoretical foundation is presented for velocity estimation with a pulsed wave (PW) Doppler system transmitting linear FM signals. The Doppler system possesses echo ranging capabilities and is evaluated in the context of Doppler ultrasound for blood velocity measurement. The FM excitation signal is formulated and the received signal is derived for a single moving particle. This signal is similar to the transmitted signal, but with modified parameters due to Doppler effect and range. The demodulated received signal is subsequently derived and analyzed. It is shown that, due to the Doppler effect, this is a linear sweep signal as well. The velocity and range information obtainable from one and two consecutively received signals are described. The latter case establishes the basis for an FM Doppler system for blood velocity measurements.     

Design and implementation of a smartphone-based portable ultrasound pulsed-wave Doppler device for blood flow measurement

Blood flow measurement using Doppler ultrasound has become a useful tool for diagnosing cardiovascular diseases and as a physiological monitor. Recently, pocket-sized ultrasound scanners have been introduced for portable diagnosis. The present paper reports the implementation of a portable ultrasound pulsed-wave (PW) Doppler flowmeter using a smartphone. A 10-MHz ultrasonic surface transducer was designed for the dynamic monitoring of blood flow velocity. The directional baseband Doppler shift signals were obtained using a portable analog circuit system. After hardware processing, the Doppler signals were fed directly to a smartphone for Doppler spectrogram analysis and display in real time. To the best of our knowledge, this is the first report of the use of this system for medical ultrasound Doppler signal processing. A Couette flow phantom, consisting of two parallel disks with a 2-mm gap, was used to evaluate and calibrate the device. Doppler spectrograms of porcine blood flow were measured using this stand-alone portable device under the pulsatile condition. Subsequently, in vivo portable system verification was performed by measuring the arterial blood flow of a rat and comparing the results with the measurement from a commercial ultrasound duplex scanner. All of the results demonstrated the potential for using a smartphone as a novel embedded system for portable medical ultrasound applications.     

A new pulsed wave Doppler ultrasound system to measure bloodvelocities beyond the Nyquist limit

Conventional pulsed wave (PW) Doppler ultrasound systems measure blood velocities unambiguously as long as the velocities are less than the Nyquist velocity. Here, a new PW Doppler ultrasound system is described, which can measure velocities up to 4.5 times higher than the Nyquist velocity. The new PW system presented here utilizes two ultrasound carrier frequencies, such that an appropriate processing of the Doppler frequencies results in an extended mean-velocity range. With this extended mean-velocity information, the complex Doppler signal is interpolated to reconstruct aliased Doppler spectra. The interpolation algorithm has been tested by computer simulations demonstrating the capabilities and limits. The integration into a commercial Doppler scanner allowed the evaluation of the new PW system in real time. In vitro and in vivo tests demonstrate the effective reconstruction of highly aliased Doppler spectra     

Isomorphism between pulsed-wave Doppler ultrasound anddirection-of-arrival estimation. II. Experimental results

For pt. I see ibid., vol. 43, no. 5, p. 911-22 (1996). Pt. I presented the basic principles for applying high-resolution wide-band direction-of-arrival estimation techniques to pulsed-wave Doppler ultrasound. Such techniques provide high-resolution velocity profiles and enable the identification of multiple velocity components inside a sample volume. Another important application is the identification and rejection of wall clutter signals. A first and essential step in applying these techniques is to convert the wide-band echoes to narrow band. The 2D DFT projection method is used for this conversion. Two different narrow-band high-resolution methods are then applied to estimate the velocity distributions; the minimum variance (MV) and the multiple signal classification (MUSIC). Experimental results are presented to illustrate the potentials and limitations of applying wide-band DOA methods to different applications in pulsed-wave Doppler ultrasound     

High resolution processing techniques for ultrasound doppler velocimetry in the presence of colored noise. Part II: Multiplephase pipe-flow velocity measurement

For pt.I see ibid., vol.50, no.3, p.267-78 (2003). This paper presents an application of continuous wave ultrasound Doppler velocity measurements to two-phase flow in pipes. In many petroleum wells, the multiphase flow is separated into two phases: the first is a liquid phase and the second is a gas phase with small scatterers. The problem of multiphase velocity profile measurements has not been satisfactorily solved by classical approaches due to the multiphase nature of the fluid and the presence of colored noise, which introduces a significant bias in classical frequency estimators. We propose the use of resolution frequency techniques to overcome the classical limitations. Direct estimation of Doppler frequency then obtained using either time frequency maximum frequency or arguments of poles of the parametric model that identifies the Doppler part of the signal is discussed. The tests made with synthetic Doppler signals and two-phase flow have demonstrated the excellent performance of the high resolution techniques based on reassignment and parametric techniques.     

Determination of the axial velocity component by a laser-Doppler velocity profile sensor

We report about the determination of the axial velocity component by a laser Doppler velocity profile sensor that is based on two superposed fanlike interference fringe systems. Evaluation of the ratio of the Doppler frequencies obtained from each fringe system yields the lateral velocity component and the axial position inside the fringe system. Inclined particle trajectories result in chirped burst signals, where the change of the Doppler frequency in one burst signal is directly related to the axial velocity component. For one single tracer particle it is possible to determine (i) the lateral velocity component, (ii) the axial velocity component including the direction, and (iii) the axial position of the tracer trajectory. In this paper we present the measurement principle and report about results from simulation and experiments. An uncertainty of the axial velocity component of about 3% and a spatial resolution in the micrometer range were achieved. Possible applications of the sensor lie in three-component velocity measurements of flow fields where only one optical access is available.     

超声多普勒信号平均频率估计方法的比较研究

本文介绍了一些常用的超声多谱勒信号平均频率估计法,并引入一种新的估计法：基于Teager算法的平均频率估计,然后分别对计算机模拟的多普勒信号和流速校刻系统的多普勒信号进行平均频率的估计和比较,给出了不同估计方法的优缺点和适用范围。     

Directional velocity estimation using focusing along the flow direction. II: Experimental investigation

For pt. I see ibid., vol. 50, no. 7, p. 857 (2003). A new method for directional velocity estimation is investigated through a number of flow rig measurements. The method uses beam-formation along the flow direction to generate data, where the correct velocity magnitude can directly be estimated from the shift in position of the received consecutive signals. The shift is found by cross-correlating the beamformed lines. The approach can find the velocity in any direction, including transverse to the traditionally emitted ultrasound beam. The method is investigated using a flow rig with a peak velocity of 0.15 m/s. A 7-MHz linear array transducer is used together with a dedicated sampling system to acquire signals from 64 transducer elements simultaneously. A technique for obtaining 128-element data using multiplexing is also presented. The data is beamformed off-line on a PC. A relative standard deviation of 1.4% can be obtained for a beam-to-flow angle of 45/spl deg/ and 4.3% at 90/spl deg/. Color flow images are displayed showing that the correct velocity magnitude can be obtained with the method for beam-to-flow angles of 60 and 90/spl deg/ with an accuracy of 3 to 4%.     

Isomorphism between pulsed-wave Doppler ultrasound anddirection-of-arrival estimation. I. Basic principles

Direction-of-arrival (DOA) estimation of signals is an important area of research in sonar and radar signal processing. Over the last few decades, numerous techniques have been developed for high-resolution DOA estimation. In this paper, we show that velocity measurement using pulsed-wave Doppler ultrasound and DOA estimation are isomorphic problems. We discuss a number of DOA methods and their potential application to flow velocity measurement using ultrasound. Wide-band DOA methods are of special interest because the pulses used for Doppler ultrasound are also wide band. These wide-band methods generally involve a preprocessing step to convert wideband signals to narrow band before applying high-resolution techniques. Application of DOA methods to Doppler ultrasound provides tools for high-resolution velocity measurement, identification of multiple velocity components within a sample volume, and clutter rejection     

Novel instrument for high-resolution ultrasound flow imaging

In multigate systems employed in Doppler flow-imaging equipment, the velocities of targets located at different ranges along the ultrasound beam axis are simultaneously detected. Typically, to reduce the computation efforts, this processing is aimed at extracting a single parameter (e.g., the mean velocity) from each signal. In this article, a novel ultrasound multigate instrument is presented capable of providing a detailed analysis of Doppler signals originated from 64 different range cells. By means of a dedicated high-speed fast-Fourier transform processor, these signals are transformed into the frequency domain without loss of information. The implementation of the new multigate system is described here, and the pieces of information which it can provide are discussed. Significant results obtained in vitro and in vivo demonstrate that the new instrument is capable of accurately reproducing the actual velocity profiles of the interrogated flow. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 438–443, 1997     

Doppler spectrum shape analysis based on the summation of flow-linespectra

A method of evaluating the shape of the Doppler spectrum in pulsed wave (PW) Doppler flowmeters in the presence of velocity gradients is presented and is demonstrated for a circular geometry transducer insonating a uniform distribution of isotropic scatterers moving in paraxial conditions. The method computes the spectrum shape by adding the power spectra of individual flow lines present in the sample volume of the moving fluid being analyzed and can be applied to any focused transducer aperture for which the flow-line spectra are known. With a parabolic velocity profile insonated by a focused circular transducer, several computed spectra are compared with experimental ones for different insonation angles; it is also shown how changes in the spectral shape, due to variations of sample volume size, can be evaluated. The results should help to provide a better understanding of PW Doppler spectrum broadening and its use in medical ultrasound diagnostics     

便携式脐血流多普勒信号多参数分析系统

文章在笔记本计算机的硬件基础上建立了脐血流多普勒信号多参数分析的便携式系统。通过计算机声卡采集脐血流音频多普勒信号，然后进行传统的声谱参数分析、零极点模型分析、Teager算子分析和分形特征分析，应用Fisher多元判据法对四类特征参数进行分类决策，从而判断胎儿的生长情况。流速实验和临床试用的结果表明，该系统是有效的，可以应用于产科的临床诊断。     

Measurement uncertainty and temporal resolution of Doppler global velocimetry using laser frequency modulation

A Doppler global velocimetry (DGV) measurement technique with a sinusoidal laser frequency modulation is presented for measuring velocity fields in fluid flows. A cesium absorption cell is used for the conversion of the Doppler shift frequency into a change in light intensity, which can be measured by a fiber coupled avalanche photo diode array. Because of a harmonic analysis of the detector element signals, no errors due to detector offset drifts occur and no reference detector array is necessary for measuring the scattered light power. Hence, large errors such as image misalignment errors and beam split errors are eliminated. Furthermore, the measurement system is also capable of achieving high measurement rates up to the modulation frequency (100 kHz) and thus opens new perspectives to multiple point investigations of instationary flows, e.g., for turbulence analysis. A fundamental measurement uncertainty analysis based on the theory of Cramér and Rao is given and validated by experimental results. The current relation between time resolution and measurement uncertainty, as well as further optimization strategies, are discussed.     

达芬振子激励分叉在多普勒频移检测中的应用

以达芬(Duffing)振子模型在单频外激励下的分叉原理为基础,提出一种可在强噪声背景下检测微弱水声探测信号多普勒频移的新方法。当达芬振子的激励振幅超过某一临界参数时系统由混沌状态突变为周期状态。根据这一原理,首先在无噪声条件下确定达芬振子由混沌状态向周期振荡转变的分叉参数阈值,然后根据噪声强度适当调节分叉参数,使得系统输出稳定在单一周期状态。当噪声中含有微弱的多普勒回波时,通过理论分析可知系统输出为阵发混沌状态,且可根据混沌状态的间隔周期较准确地求出回波信号的多普勒频移。     

Experimental evaluation of velocity and power estimation forultrasound blood flow imaging, by means of a two-dimensionalautocorrelation approach

This paper evaluates experimentally the performance of a novel axial velocity estimator, the 2D autocorrelator, and its Doppler power estimation counterpart, the 2D zero-lag autocorrelator, in the context of ultrasound color flow mapping. The evaluation also encompasses the well-established 1D autocorrelation technique for velocity estimation and its corresponding power estimator (1D zero-lag autocorrelator), to allow performance comparisons under identical conditions. Clutter-suppressed in vitro data sets from a steady-flow system are used to document the effect of the range gate and ensemble length, noise level and angle of insonation on the precision of the velocity estimates. The same data sets are used to examine issues related to the estimation of the Doppler signal's power. The first-order statistics of power estimates from regions corresponding to flow and noise are determined experimentally and the ability of power-based thresholding to separate flow signals from noise is characterized by means of ROC analysis. In summary, the results of the in vitro evaluation show that the proposed 2D-autocorrelation form of processing is consistently better than the corresponding 1D-autocorrelation techniques, in terms of both velocity and power estimation. Therefore, given their relatively modest implementation requirements, the 2D-autocorrelation algorithms for velocity and power estimation appear to represent a superior, yet realistic, alternative to conventional Doppler processing for color flow mapping     

一种提高多普勒测速仪测频精度的方法

多普勒测速仪是水面或水下平台速度测量的主要设备。提出了利用随机样本一致(Random Sample Consensus,RANSAC)算法来估计多普勒频移,从而使速度测量具有更高的稳定性。多普勒测速仪信号处理的核心是测量多普勒频移,该方法利用回波复相关相位是多普勒频移的一次函数来估计多普勒频移,进而计算得到平台速度,在估计频移时采用RANSAC算法以提高测频精度。为了验证方法有效性,对信号形式为连续波(Continuous Wave,CW)脉冲对的情形进行了仿真。结果表明,提出方法的稳定性得到明显提高。     

Accurate Doppler angle estimation for vector flow measurements

Traditional Doppler methods measure only the axial component of the velocity vector. The lack of information on the beam-flow angle creates an ambiguity that can lead to large errors in velocity magnitude estimates. Different triangulation techniques so far have been proposed, which basically perform multiple measurements of the Doppler frequency shift originating from the same region. In this work, an original approach is introduced, in which two ultrasound beams with known relative orientation are directed toward the same vessel, but only one of them is committed to perform a Doppler measurement; the second (reference) beam has the specific task of detecting the beam-flow angle. The latter goal is obtained by accurately identifying the achievement of the target 900 reference-beam-to-flow angle through the inspection of the backscattered Doppler signal spectrum. In transverse flow conditions, in fact, such spectrum is expected to be centered on the zero frequency, and even small deviations from the desired 900 orientation cause noticeable losses of spectral symmetry. Validation of the new method has been performed through experimental tests, which show that the beam-flow angle can be estimated with high accuracy (rms errors lower than 1 degree), and repeatable velocity magnitude measurements are possible. A procedure for automatically tracking the desired orientation by the reference beam is also introduced and shown suitable for implementation in steerable linear array transducers.     

Spectral Doppler estimation utilizing 2-D spatial information and adaptive signal processing

The trade-off between temporal and spectral resolution in conventional pulsed wave (PW) Doppler may limit duplex/triplex quality and the depiction of rapid flow events. It is therefore desirable to reduce the required observation window (OW) of the Doppler signal while preserving the frequency resolution. This work investigates how the required observation time can be reduced by adaptive spectral estimation utilizing 2-D spatial information obtained by parallel receive beamforming. Four adaptive estimation techniques were investigated, the power spectral Capon (PSC) method, the amplitude and phase estimation (APES) technique, multiple signal classification (MUSIC), and a projection-based version of the Capon technique. By averaging radially and laterally, the required covariance matrix could successfully be estimated without temporal averaging. Useful PW spectra of high resolution and contrast could be generated from ensembles corresponding to those used in color flow imaging (CFI; OW = 10). For a given OW, the frequency resolution could be increased compared with the Welch approach, in cases in which the transit time was higher or comparable to the observation time. In such cases, using short or long pulses with unfocused or focused transmit, an increase in temporal resolution of up to 4 to 6 times could be obtained in in vivo examples. It was further shown that by using adaptive signal processing, velocity spectra may be generated without high-pass filtering the Doppler signal. With the proposed approach, spectra retrospectively calculated from CFI may become useful for unfocused as well as focused imaging. This application may provide new clinical information by inspection of velocity spectra simultaneously from several spatial locations.     

频率调制多普勒全场测速实验系统测试

频率调制多普勒全场测速技术是一种基于分子滤波和多普勒频移现象的流场速度测量方法,在高速、超高速及大尺度风洞流场测量方面潜力巨大.我们设计开发了采用CCD相机作为接收探头的FM-DGV实验系统,该系统主要包括激光器、片光光学系统、碘分子滤波器、图像采集相机、频率监测单元等.基于该系统进行了谐波幅值比和转盘线速度测试实验.实验结果表明,该实验系统工作正常,速度测量误差最大值小于2m/s.     

基于线性调频信号二次相位变换的主动声呐目标速度估计

分数阶傅里叶变换常用于主动声呐线性调频信号的分析,通过搜索变换参数可以估计目标的相对速度.但是由于其参数搜索计算量偏大,在自主式水下航行器等计算力有限的小平台难以实时处理.针对该问题提出了一种基于二次相位变换的线性调频信号速度估计方法,根据多普勒频移后线性调频信号的二次相位变换的解析解,分析了二次相位变换后变换域频谱展...