A review of the measurement of blood velocity and related quantities using Doppler ultrasound

Ultrasound systems can be used to investigate blood flow by use of the Doppler effect. The flow information may be displayed as either a real-time sonogram or a two-dimensional colour image. Estimates of maximum velocity using commercial systems are in error by typically 10-100 per cent; this is associated with the inability of the single-beam Doppler method to measure the true direction of flow, and with geometric spectral broadening. Vector Doppler systems acquire Doppler information along two beam directions and are able to measure accurately the velocity and direction of motion within the scan plane. The small beam width of modern Doppler systems means that the condition of uniform insonation, required for estimation of mean velocity from mean frequency shift, is not valid except for the very smallest vessels. Other quantities related to the velocity may also be estimated, such as the volumetric flow and wall shear stress. Flow visualization using colour flow imaging suffers from dependence of the displayed colour on the direction of blood motion. The vector Doppler technique may be extended to colour flow to give improved visualization of flow, in which there is no angle dependence within the scan plane.     

Ultrasonic fingerprint sensor in underglass prototype using impedance mismatching

Fingerprint imaging is a powerful tool in biometric identification systems. There are several methods for measuring fingerprints, such as optics, capacitive, and ultrasonic methods. The previous ultrasonic imaging techniques have been available in immersion systems which require the hands to be put into water. Also, pulse-echo system in dry condition has coupling layer which is similar acoustic impedance to human tissue or high impedance materials based on waveguide. For fingerprint imaging in the dry state, we propose an ultrasonic imaging technique in underglass by using the impedance mismatch between the fingertip and the solid plate. We present the image results according to the plate material such as acrylic, glass and PDMS. In addition, simulation results based on small 2-D array transducers in a near field suggest the feasibility of compact and fast fingerprint scanning system. Therefore, this work presents feasibility of ultrasonic pulse-echo fingerprint sensing method for dry hand.     

Human left main coronary artery blood flow: noninvasive Doppler echocardiography with sample volume tracking

We developed sample volume tracking units that controlled the pulsed ultrasonic Doppler sample volume location in relation with the anterior-posterior movement of the human left main coronary artery (LMCA). Combined with noninvasive Doppler echocardiographic mechanical sector scanners (DS), the trackers controlled the axial location of the sample volume by range gate control. The Doppler angle was minimized with the long axis of the imaged LMCA. Both stored waveform, memory-driven (MD) and real-time (RT) trackers were developed. These devices were used to measure blood velocity spectral waveforms and lumen diameters, which were used to calculate flow. Using the RT tracker, we compared DS measurements with known flows (0-1000 ml/min) in a moving 4 mm tygon tubing phantom (r = 0.92, SEE = 32 ml/min). Using the MD tracker, we compared the DS with simultaneous invasive flow measurements in 11 patients with angiographically normal coronaries and ventricular function during cardiac catheterization. Using the RT tracker, we compared the DS measurements with subsequent nonsimultaneous, invasive flow data in 8 similar patients. Invasively determined flows were calculated from angiographic diameters and blood velocities which were obtained with a Doppler velocimeter catheter. Regression coefficients (r) were: (Table: see text). V = maximum velocity, D = diameter, Q = mean flow, *p less than .05 Interoperator and intraoperator variabilities in vivo of DS measurements with RT tracking were 21% and 15%, respectively. We conclude that Doppler echocardiography with either MD or RT sample volume tracking may be of limited clinical usefulness in the noninvasive measurement of phasic left main coronary artery blood flow in unselected patients.     

选带细化超声流量计试验分析

文中研究一种用于工业密闭管道流体流量测量的新型超声波多普勒流量计。采用中频调制为基础提取流体流速的方向信息，引入选带细化频谱分析技术（Z00M—FFT）对解调后的超声波多普勒信号进行频谱估计，并以此为基础计算管道流量。该方法能判断流速的方向；降低流速测量下限；提高了流速测量的动态响应速度、实时性以及稳定性。实验表明选通细化超声流量计准确度等级为1．5级。     

Ultrasonic speckle correlation imaging of 2D particle velocity profiles in multiphase flows

Two-dimensional ultrasonic speckle correlation velocimetry (USV) is a new technique that allows imaging of moving scattering media, at a high frame-rate. In this paper we apply the technique to determine two-dimensional particle velocity profiles of multiphase flows. Experiments are realized with suspensions of Sonazoid (medical contrast agent) and Magnetite (Fe₃O₄) in water. All measurements are performed in a vertical pipe with the flow moving downwards. The two-dimensional particle velocity profiles are then compared with a reference liquid volume flow velocity. As expected from theory, the heavier Magnetite particles have slightly higher velocity than the liquid, whereas the contrast agent simply follows the liquid motion.The proposed technique can be used in combination with other techniques to measure the mass flow of the solid phase, in solid/liquid multiphase flow. This is generally more interesting than measuring the bulk mass or volume flow.     

Doppler spectrum analysis and flow pattern identification of oil-water two-phase flow using dual-modality sensor

Horizontal oil-water two-phase flow widely exists in petroleum and chemical engineering industry, where the oil and water are usually transported together. As one of most importance process parameters to describe the two-phase flow, the flow pattern can reflect the flow characteristics of inner flow structure and phase distribution. The identification of flow pattern will contribute to develop more accurate measurement model for flow rate or phase fraction and ensure the safety and efficiency of operation in industry. A dual-modality sensor combining with continuous wave ultrasonic Doppler sensor (CWUD) and auxiliary conductance sensor, was proposed to identify flow patterns in horizontal oil-water two-phase flow. In particular, the oil-water flow characteristic was analyzed from Doppler spectrum based on the CWUD sensor. Besides, the dimensionless voltage parameter based on conductance sensor was applied to provide the information of continuous phase in the fluid. Several statistical features were directly extracted without any complicated processing algorithm from Doppler and conductance signals. The extracted features are put into a multi-classification Support Vector Machine (SVM) model to classify five oil-water flow patterns. The results show that the overall identification accuraccy of 94.74% is satisfactory for horizontal oil-water two-phase flow. It also demonstrates that the noninvasive ultrasonic Doppler technique not only can be used for flow velocity measurement but also for flow pattern identification.     

基于DSP的新型超声多普勒流量计设计与实现

文中针对当前工业管道用超声多普勒流量计的性能普遍不高的现状,改进了测量工业管道流量方法,并且采用高速DSP器件TMS320VC5410实现一种新型超声多普勒流量测量系统.实现的新型超声多普勒管道流量测量系统可以动态显示流速和方向、瞬时流量、累积流量、信号强度等测量结果,较高的流速测量动态响应能力以及稳定性,具有较好的推广和应用前景.     

Ultrasonic investigation of blood flow.

Ultrasound and the Doppler effect are used to measure blood velocity non-invasively in order to diagnose blood vessel disease. Intrusive lesions on arterial walls give rise to an alteration of the time-varying blood velocity waveform and local blood flow disturbance which are detected and measured using the envelope and width of the Doppler signal spectrogram respectively. Flow may also be imaged in colour superimposed on a grey-scale anatomical image allowing vessel narrowing and the accompanying flow disturbance to be visualized. Developments in three-dimensional imaging, angle tolerant velocity measurements and increased sensitivity using second harmonic backscatter from encapsulated-bubble contrast media ensure increasing use of this modality.     

基于超声造影剂谐波图像的流场测量技术

本文研究了基于超声造影剂的血流运动场估计与显示技术,通过在血液中注入超声造影剂作为示踪粒子,对造影谐波图像进行时域相关处理,可得到成像部位的二维流场分布图。相对于常规Ｄｏｐｐｌｅｒ方法中用Ｄｏｐｐｌｅｒ回波信号的频偏计算流速值,该技术可直接从超声图像提取与夹角无关的流速矢量信息。本文通过流动模型验证该方法,浸入超声水槽中的乳胶管中流动着血液替代品,沿水流方向进行超声成像,对实验所得的造影后的Ｂ超图像以及谐波图像,用一种节省计算量的多尺度相关算法进行处理,并相互比较。结果显示,谐波图像相对Ｂ超基波图像具有更高的信杂比,从根本上解决了基波图像低信噪比对时域相关测量精度的限制,可以得到与夹角无关的二维血流场分布图,该方法是医学和有关工业领域中超声流场测量的一种有效的方法。     

超声多普勒谱修正的油水两相流流速测量

针对水平管道油水两相流流速的无扰动测量问题,提出一种基于超声/电学双模态传感器的流速测量方法。测量系统由连续波超声多普勒传感器和基于电容与电导的电学传感器构成,分别用于获取两相流流速和分相含率。由于连续波多普勒的测量区域集中于管道中心,受流速剖面、含率分布影响,所测得流速并非流体的总表观流速。在假设含率分布满足高斯分布的前提下,建立相含率加权的多普勒能量谱模型,将含率分布的影响因素引入总表观流速的测量,并建立总表管流速和分相表观流速的计算模型。在试验基础上,分别确定水连续和油连续时总表观流速计算模型的参数。试验表明,通过模型计算出的表观流速与实际测量的流速能够较好吻合,总表观流速的相对误差小于6.32%,分相表观流速的方均根误差小于5.64%。     

光声血流速度测量方法及研究进展

光声成像因其独特的成像原理,兼顾了功能性和分辨率,对诊断和处理心血管疾病具有十分重要的意义。通过对光声血流速度测量进行综述,系统介绍了光声多普勒、光声显微成像和光声相关谱三个原理下的血流速度测量原理及具体应用,以期对此领域的研究人员的研究提供参考。     

Note: Measurement method for sound velocity of melts in large volume press and its application to liquid sodium up to 2.0 GPa

Based on large volume press and conventional pulse-echo ultrasonic technique, we have overcome the difficulty in determining the length of liquid specimen under high pressure, and the sound velocity in liquid Na has been measured up to 2 GPa. The P-V data deduced by our sound velocity results through equation of state is in an excellent agreement with previous data directly determined by piezometer method. This new experimental technique is convenient and ready for use, being expected to advance investigation on thermodynamic properties of liquid metals and other melts under high pressure.     

Matching pursuit for decomposition and approximation of ultrasonic pulse-echo wavelet and its application in ultrasonic nondestructive evaluation

The estimation of the time of arrival (TOA) and/or time of flight of the ultrasonic echoes is essential in ultrasonic nondestructive evaluation. In this paper, matching pursuit method has been used to analyze noisy ultrasonic pulse-echo wavelet and decompose the noisy pulse-echo wavelet into unit-norm vectors. The error ratio of the mean square is used to monitor the acceptability of the unit-norm vector obtained by the matching pursuit performance. A matched filter can be designed by using the time reversal of the approximation pulse-echo wavelet obtained by the reconstruction result with several large coefficient decomposed unit-norm vectors. After performing the matched filter, the part of the signal related to the electrical noise will be removed leaving only the correlated portion of the ultrasonic echoes. Then no initial phase have been contained in the processed ultrasonic echoes. Therefore, the TOA can be estimated directly from the peaks of the representation of the processed signal. Numerical simulations and experimental results make evidence the good performance of the proposed approach which has good effect of noise suppression and results in much improved accuracy in the estimation of echo arrival time.     

Experimental study to establish an evaluating method for the responsiveness of liquid flowmeters to transient flow rates

An aim of this research work is to establish an evaluation method concerning a responsiveness of flowmeters for a transient flow rate. To this end, reference flow metering systems for the transient flow are proposed in this paper. Because a behavior of the responsiveness depends on the type of flowmeter, evaluations using different parameters, such as response time to sudden rise and sudden fall in flow rate, response to the frequency and amplitude of flow pulsation, mean characteristic and so on are needed. To achieve a precise evaluation, two reference flow metering methods for transient flow rates are proposed in this paper. One is a high-response weighing method and the other is a velocity profile measurement method using the ultrasonic pulsed Doppler method (UPDM). Since the behaviors of the transient flow rate measured by both methods show good agreement, we conclude them to be useable as a reference flow metering system.     

Ultrasonic pulse-Doppler flow meter application for hydraulic power plants

At hydraulic power stations, Pitot tubes have commonly been used to measure flow rates in steel penstocks for performance testing of hydraulic turbines. Due to the difficulties of Pitot tube installation, transit-time ultrasonic flow meters are becoming a popular replacement, but their accuracy is sensitive to velocity profiles that depend on Reynolds numbers and pipe surface roughness. Ultrasonic pulse Doppler flow meters have recently gained favor as suitable tools to measure flow rates in steel penstocks because they can measure instantaneous velocity profiles directly. Field tests were conducted at an actual hydraulic power plant using an ultrasonic pulse Doppler flow meter, and it was found capable of measuring velocity profiles in a large steel penstock with a diameter of over one meter and Reynolds number of more than five million. Furthermore, two ultrasonic transducers were placed on the pipe surface to validate the multi-line measurement of asymmetric flow. Each transducer recorded the velocity profile simultaneously from the pipe centerline to its far wall during plant operation. Velocity profiles were obtained from three-minute measurements to improve the accuracy of flow rate measurements.     

Use of gas bubbles for ultrasound Doppler flow velocity profile measurement

Ultrasonic velocimetry based on the Doppler shift effect accurately provides quasi-instantaneous flow fields for fluids with a sufficiently high acoustic scattering level. However, ultrasonic velocity instruments are known to perform poorly in clear water with low acoustic scattering level, which are frequent conditions in laboratory applications. This work confirms a technique to solve the problem by seeding the flow with micro hydrogen bubbles, generated by means of electrolysis.This paper investigates the influence of gas bubbles density on the quality of the ultrasound Doppler based velocity profiles in an open channel flow. The bubbles are generated by electrolysis of water using different magnitudes of electrical current. The estimation of the number of bubbles in the measurement volume confirms that the bubble diameter is similar to that of the wire used for electrolysis. This enables to determine the minimum density of gas bubbles needed to obtain a reasonably good echo and therefore an accurate velocity profile.     

矩阵换能器超声三维成像方法研究*

针对常规超声检测难以直观地显示被检对象缺陷的形状及走向等问题,开展矩阵换能器超声三维成像方法研究。超声三维成像技术具有直观显示被测对象内部缺陷三维特征的优点,基于矩阵换能器的超声三维成像方法具有扫查速度快、分辨率高等优点,是当前超声三维成像技术的研究热点。本文介绍了矩阵换能器体扫查原理及其控制方法;提出了矩阵换能器体扫查时三维体数据采集方法和数据融合算法;基于矩阵换能器和相控阵板卡系统对铝标样等试样进行了体扫查检测实验,采用等值面和体绘制两种算法对缺陷进行三维成像,并对单一缺陷进行了定量分析,定量精度较高。研究结果表明,矩阵换能器超声三维成像方法能够表征缺陷的三维形貌特征,在无需移动换能器的情况下便可实现缺陷三维检测,是超声三维检测的有效方法。     

Measurement of tissue motion.

A number of ultrasonic methods are available for the detection of tissue motion as it occurs physiologically in the body. The detection of echoes from within the body in less than 1 ms after the initial transmission of ultrasound and the Doppler effect have enabled a range of instrumentation to be developed. The subject owes a great deal to advances in transducer design, electronics and computer technology. Over many years fast B-mode imaging and M-mode traces of boundary position versus time have been the main clinical tools. Currently new sophisticated detection and imaging techniques are being produced based on the Doppler effect and on tracking motion in tissue images. The measurement of several velocity components is permitting velocity vectors to be determined more completely, adding to accuracy. Not surprisingly, cardiology is the main field of application but there are other areas of interest, e.g. vascular, musculo-skeletal and foetal function studies.     

Velocity vector profile measurement using multiple ultrasonic transducers

This paper proposes a new technique that enables the measurement of the velocity vector in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on the ultrasonic velocity profiling by using multiple transducers. A two-dimensional system was constructed and successfully applied to an actual flow field for two-dimensional velocity vector measurements. To estimate the influence of the existence of a wall, acoustic field under the developed system was calculated by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure the two-directional velocity components of a periodic velocity fluctuation in the wake of a cylinder as an example of unsteady flow. Temporal variation of velocity vector profiles well represent the velocity fluctuation, and vorticity distribution, which is obtained from the spatial distribution of velocity vector, well represents the vertical motion in the wake.