Power Doppler ultrasound evaluation of the shear rate and shearstress dependences of red blood cell aggregation

The use of power Doppler ultrasound at 10 MHz is evaluated as a method to study the shear rate and the shear stress dependences of red blood cell aggregation. This evaluation was based on 6 in vitro experiments conducted in a 1.27-cm diameter tube under steady flow conditions. Porcine whole blood was circulated in the flow model at flow rates ranging between 125 to 1500 ml/min (mean shear rate across the tube ranging between 6 and 74 s^-1). For each flow condition, the variation of the Doppler power across the tube and the velocity profile were measured by moving the Doppler sample volume across the tube diameter. For each radial position, the shear rate within the Doppler sample volume was also determined by considering the radial power pattern of the ultrasound beam. To estimate the shear stress within the Doppler sample volume, the apparent viscosity of blood samples withdrawn from the flow model was measured for each experiment. The variation of the Doppler power as a function of the shear rate within the sample volume showed a rapid reduction of the power between 1 and 5 s^-1, a transition region between 5 and 10 s^-1, and a very slow reduction beyond 10 s^-1. Little variation of the Doppler power was measured for shear stress higher than 2 dyn/cm. The maximum Doppler power for all flow rates was usually found near the center of the tube. Based on the ultrasonic scattering models, which predict that the Doppler power is related to the volume square of the scatterers, the method described in the present study showed a very high sensitivity to the presence of red blood cell aggregation for shear rates below 10 s^-1     

The effects of hematocrit, shear rate, and turbulence on ultrasonicDoppler spectrum from blood

Previous studies of ultrasonic scattering properties of blood using a pulse-echo experimental arrangement show that ultrasonic backscatter from blood is influenced by a number of factors including hematocrit, shear rate, and the nature of flow (J. Acoust. Soc. Amer., vol. 75, p. 1265, 1984 and J. Acoust. Soc. Amer., vol. 84, p. 1, 1988). Since the Doppler frequency spectrum from a Doppler flowmeter is derived from echoes backscattered by red blood cells in the flowing blood, it is also undoubtedly a function of these parameters. The effects of these parameters on Doppler spectrum from blood have been investigated using a pulsed Doppler flowmeter. The results agree well with those obtained in previous studies. One important conclusion of this study is that the assumption that the Doppler spectral power density at a frequency in Doppler spectrum is linearly proportional to the number of red cells flowing at that velocity used in many theoretical models developed to explain the Doppler phenomenon may be erroneous. An alternative is proposed. It is shown that conclusions derived from these theoretical models would remain valid by making this assumption.     

超声多普勒流量模拟器研究

相对传统的流量计,超声多普勒流量计测量适合于多种工况条件和液体类型的流量测量,在工业流量测量中具有广泛的应用前景。为了适应多普勒流量计性能测试和评估的需要,加快流量计的研制进程,本文通过对油田应用环境的分析,提出了基于DDS（直接数字式频率合成）技术的多普勒流量模拟器的设计。完成了硬件、固件程序及计算机软件的开发。应用...     

基于超声多普勒的井下多相流量测量控制系统

本文主要介绍了一种适于油气田开发的井下超声波多普勒流量测量控制系统,该装置系统采用声学多普勒原理,通过控制超声波传感器的一对高精度换能器分别发射和接收超声波信号,并由流量计的硬件系统、TMS320F28335的数据信号处理器获取油管中的多普勒频移,计算出瞬时流量与累计流量,实现对油管中的油、气、水三相流进行实时在线流速测量和总体积流量测量,为生产系统提供一个比较准确的实时流速及总体积流量,以便对系统进行准确的管理及控制。实验证明,测量精度可达2%～3%。     

Analysis of pulsed wave Doppler ultrasound spectra obtained from amodel intracoronary catheter

Abnormal arterial blood flow patterns have been implicated in the evolution of various vascular disease processes. Intravascular ultrasound techniques using the pulsed wave Doppler catheter offer the opportunity to characterize these abnormal flow patterns. The authors have developed a mathematical model that predicts the first two moments of the Doppler spectrum obtained using a Doppler catheter based on the distribution of ultrasonic beam power and velocity profile of fluid flow with an arbitrary distribution of flow disturbances. A scaled-up, in vitro experimental arterial system was used to confirm the validity of the model. Comparison of the predicted first two moments of the Doppler spectrum to the experimental values in this system demonstrated that the distribution of beam power significantly affects the magnitude of the first two moments. Additionally, both velocity gradient and velocity fluctuation broadening effects play prominent roles in determining the magnitude of the second moment. These phenomena must therefore be considered when evaluating in vivo Doppler spectra used for the characterization of abnormal flow patterns     

Integrated circuits for a bidirectional implantable pulsed Doppler ultrasonic blood flowmeter

The application of integrated circuits in medical implants and the complexity of these implants have increased at a rapid pace in the past few years. The need, however, still exists for a highly accurate and stable telemetry system for the measurement of blood flow. Two custom-designed ICs have been realized to resolve this problem. These ICs form the heart of a totally implantable pulsed Doppler ultrasonic bidirectional blood flowmeter; one circuit performs the basic timing functions, and the second implements low-level linear signal processing. For a small implanted package (3.8/spl times/2.8/spl times/0.8 cm/SUP 3/), these ICs must meet the stringent requirements of low-voltage operation (2.2-2.8 V), low power (<40 mW), high stability (short-term timing jitter <50 ppm), and the minimum of external components. Using a quadrature direction detecting technique, the circuits sense both positive and negative flow and produce a multiplexed telemetry signal. The approach used minimizes parts count and power drain and maximizes channel-to-channel matching in the multiplexed signal.     

Frequency-Dependent Attenuation Effects in Pulsed Doppler Ultrasound: Experimental Results

The quantitative capability of pulsed Doppler ultrasound in clinical practice is limited by the effects of frequency-dependent attenuation of ultrasound in tissue, as well as several other spectral-broadening mechanisms which distort the Doppler spectrum of an ultrasonic echo. In this communication, we present results of in vitro experiments which demonstrate the magnitude of the errors expected in clinical measurements of blood flow parameters when frequency-dependent attenuation Of ultrasound in biological tissue is ignored. It is shown that errors as large as 15 percent may occur in Doppler measurements of blood flow velocity through 7 cm of intervening tissue. A comparison is also made between experimental results and a theoretical model which includes the effects of scattering and attenuation.     

Optimal System Design for an Implantable CW Doppler Ultrasonic Flowmeter

A totally implantable telemetry system utilizing custom micropower monolithic integrated circuits has been developed to measure instantaneous pulsatile blood flow in the major arteries of animals. The device utilizes the Doppler effect at ultrasonic frequencies to achieve a flowmeter possessing small size and weight, low power consumption, inherent accuracy, and long-term stability. The integrated circuit electronics package occupies a volume of 3.8 cc and requires a power consumption of 10 mW from a single 135 volt mercury cell. The volume of the entire implantable flowmeter package is less than 36 cc. As a micro-miniature radio-telemetry system, the flow-meter can be totally implanted within the body, thereby eliminating the need for wires penetrating the skin, a serious problem with "back-pack" flowmeters due to danger of infection. The implantable flow-meter system provides a new and necessary tool for accurate quantitative measurements in the study of cardiovascular disease. It has been used in the study of transplanted heart rejection to monitor blood velocity in the major arteries of doB     

Pitfalls Using Doppler Ultrasound to Transduce Blood Flow

General testing procedures which will ascertain whether a Doppler ultrasonic blood flowmeter is correctly designed and operating properly are presented. A commercial Doppler ultrasonic blood flowmeter using the procedure is evaluated. Two pitfalls were encountered which prevented its proper operation. High-frequency response was inadequate, which introduced a nonlinearity into the input-output calibration curve. Low-frequency gain was too high, resulting in wall-motion artifacts. These problem areas are described in detail, and a remedy for each is suggested.     

Evaluation of a Laser Doppler Flowmeter for Measurement of Tissue Blood Flow

An instrument for measurement of tissue blood flow based on the laser Doppler principle was evaluated using a fluid model. A unique and linear relationship between flowmeter response and flux of red cells was demonstrated with red cell velocities and volume fractions within the normal physiological range of the microcirculatory network of the skin. Different degrees of oxygenation proved to influence the Doppler signal only to a minor extent. The study also shows that the Doppler signal is formed essentially by heterodyne mixing of light beams backscattered in static structures and moving red cells.     

The Performance of the Ultrasonic Flowmeter in Complex Velocity Profiles

The principle of operation of the ultrasonic flowmeter, detecting phase shifts or pulse transit times, is examined. It is shown both theoretically and experimentally that the sensitivity of the flowmeter depends on the fluid velocities averaged along the path of the ultrasound between the transducers. The instrument therefore overestimates the net fluid velocity by 33 percent in case of steady laminar flow and by approximately 7 percent in case of steady turbulent flow, provided the ultrasound traverses the entire lumen of the (cylindrical) vessel. The signal obtained in case of oscillatory flow generally is larger in amplitude than and lagging in phase behind the true flow. The errors are between 0 and 33 percent and between 0 and 7°, respectively. The effect of this on natural blood flow signals is discussed in detail. It is concluded that the flowmeter detects the waveform of aortic flows with a fidelity which should be satisfactory in most cases.     

An intelligent multiplexer/driver integrated circuit for animplantable multichannel blood flowmeter

A custom CMOS integrated circuit that extends the current implantable single-channel ultrasonic pulse Doppler blood flowmeter to three channels is discussed. By operating on a single 2.7-V battery with three existing custom bipolar ICs, the integrated circuit serves as an RF command receiver, controls the channel-multiplexing sequence, and multiplexes the piezoelectric transducers. A round-trip channel isolation of 38 dB is achieved with a novel transducer-multiplexing circuit that employs three on-chip power transistors for 6-MHz transducer excitation. Each power transistor is capable of switching a current of 200 mA with an on-resistance of 3 Ω and transition times of 10 ns. The power consumption in the implanted portion of the three-channel flowmeter is only 0.8 mW higher than the 30 mW in the single-channel flowmeter     

基于TDC-GP2的时差式超声流量计的设计

为实现流体流量测量高精度和低功耗的设计目的,采用TDC-GP2高精度低功耗测时模块,设计了一种基于ATmega32的时差式超声流量计。通过实验测量管径为20mm的管道中的家用自来水流量,得到系统测量精度为±1%,LCD上动态显示瞬时和累计流量以及电池电量等参数,同时可以通过RS 232与外部通信,便于大规模应用时由上位机对信息统一管理。     

基于Modbus协议的超声波水流量计的设计

为了更好地将超声波水流量计检测的数据进行远程传输,本设计根据超声波水流量计的测量原理和Modbus通信协议,实现了基于Modbus协议的超声波水流量计的设计.介绍了基于MSP430微处理器并搭载高精度计时芯片TDC-GP22构成的基本功能电路.同时介绍了信号处理电路设计与仿真以及RS485通讯模块接口电路.在软件设计上...     

A Stochastic Model of the Backscattered Doppler Ultrasound from Blood

A stochastic model of the continuous wave (CW) Doppler ultrasound signal backscattered from blood is developed. The model incorporates the effects due to the flow-dependent packing and aggregation of red blood cells (RBC's) at a given hematocrit. The Doppler signal is shown to be a zero-mean, stationary, Gaussian random process which can be completely specified by its autocorrelation function. From the autocorrelation function, explicit closed-form expressions are derived for the power spectral density and the backscattering coefficient. Both expressions are found to be more general than those derived from previous blood models. Further, the values of the statistical parameters in the model are discussed in relation to recently published data on the backscattering coefficient of bovine RBC's suspended in saline and of bovine whole blood. It is shown that the change in backscatter with flow conditions can be explained by RBC orientation in saline and by RBC aggregation in whole blood.     

Design and Construction of a Pulsed Ultrasonic Air Flowmeter

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory air flow is calculated by measuring the transit times of short ultrasonic pulse-trains simultaneously transmitted upstream and downstream at a 650 Hz rate. The flowmeter system consists of a control unit and a separate flowhead. The former includes the power supplies, a controlling microprocessor, most of the signal processing circuitry, and three analog outputs for flow, volume, and temperature, respectively. The flowhead contains the respiratory tube with a constant circular cross section (length 90 mm, diameter 20 mm, dead space 35 cm3), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory air flowmeter is extremely fast (response time 1-2 ms) and accurate, with low noise (below 9ml/s), with a wide flow range (bidirectional from 0 to 9 l/s) and with a linear frequency response up to 70 Hz.     

眼部超声Doppler血流计的研制

眼部正常的血液供应是维持眼部组织正常生理功能的基础。该文介绍了一种无创检测眼部血流速度瞬时相对变化和眼部血流状况的超声Doppler血流计,该血流计由超声波信号发生器、超声波换能器、放大器、混频器、A/D转换器和微型计算机等组成,可实时、在体、无创检测眼部血流速度和血容量的相对变化,具有结构简单、使用方便等特点。     

Flow quantification in valvular heart disease based on the integralof backscattered acoustic power using Doppler ultrasound

The noninvasive quantification of pathologic backflow, referred to as regurgitant flow, associated with valvular heart disease has been an elusive medical goal. To date, techniques based on ultrasound have been unsatisfactory due to weak assumptions and indirect estimations. Here, instead, we propose to estimate regurgitant flow directly from the Doppler spectrum of the backscattered ultrasound. Since backscattered spectral power is proportional to the sonified blood volume and spectral frequency is directly related to velocity, power times velocity should be proportional to flow. To date, however investigators have assumed this held only for laminar flow, not for regurgitant jets in which turbulence augments backscatter. We demonstrate that this challenge can be overcome by analyzing the Doppler spectrum at the origin of the regurgitant jet, where flow is laminar since turbulence has not yet developed. We present in vitro and in vivo data that demonstrate that there is a linear proportionality between regurgitant flow and the integral of Doppler power times velocity (PVI). Power measurements were also calibrated by applying a dual-beam technique, providing absolute values of flow rate and volume in vivo. In our work we demonstrate that in patients with valvular heart disease, this new PVI technique allows for the measurement of regurgitant flow directly and noninvasively for the first time, overcoming the limitations of current techniques     

Sizing emboli in blood using pulse Doppler ultrasound. I.Verification of the EBR model

An experiment to verify a theory describing ultrasound backscattering from emboli in flowing blood is presented. The theoretical predictions for the backscattered power versus embolus size are based on the measurement of the embolus to blood ratio (EBR) of backscattered acoustic power. This tool is necessary for in vivo clinical application because it removes the need to characterize attenuation and reflection loss in heterogeneous tissue. The experiment presented utilizes a customized ultrasound pulse Doppler that is capable of interrogating a sample volume with two different frequencies concurrently. A flow circuit including a 3.6-mm-diameter conduit in polyacrylamide gel in which emboli are observed with the dual frequency Doppler is described. The flow within the circuit has acoustic backscatter coefficient similar to blood due to a calibrated concentration of 31.1-μ diameter polystyrene microspheres. Polystyrene microsphere “emboli” having nominal diameters of 161 and 239 μ are placed in this flow loop and time series Doppler shift signatures are recorded. These signatures are investigated and a refraction artifact hypothesis is proposed to explain systematic deviation of the signatures away from theoretically expected results. Results show that gross discrimination of embolus size is feasible     

Unambiguous measurement of volume flow using ultrasound

A new modality for transcutaneous measurement of blood flow is described. Two ultrasonic pulsed Doppler techniques (Doppler imaging and average Doppler shift detection) are combined to measure net flow across an arbitrary sample plane. This estimate of volume flow is independent of lumen shape, orientation, and velocity profile.