利用超声回波跟踪技术测量血流速度的实验研究

文章主要介绍了利用超声回波跟踪技术进行血流速度测量的原理和方法,通过对运动弦线速度的测量实验,比较了这种方法和传统的超声多谱勒技术在血流速度测量上的性能差异。     

Application of ultrasonic velocity measurement for flow stress determination of TWIP steel

Abstract

In the present work, the ultrasonic velocity measurement was used as a non-destructive technique for flow stress determination of a twinning induced plasticity steel. For this purpose, first, a relationship between mechanical twinning and ultrasonic velocity was found out and then, it was used in the flow stress model previously suggested by the authors. Comparison of the obtained results with the experimental values revealed a good agreement.     

Decorrelation-based blood flow velocity estimation: effect of spread of flow velocity,linear flow velocity gradients,and parabolic flow

In recent years, a new method to measure transverse blood flow, based on the decorrelation of the radio frequency (RF) signals has been developed. In this paper, we investigated the influence of nonuniform flow on the velocity estimation. The decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter are studied by means of computer modeling. Blood was simulated as a collection of randomly located point scatterers; moving this scattering medium transversally across the acoustical beam represented flow. First-order statistics were evaluated, and the signal-to-noise ratio from the signals were measured. The correlation coefficient method was used to present the results. Three velocity profiles were simulated: random spread of blood-flow velocity, linear blood-flow velocity gradient, and parabolic blood-flow. Radio frequency and envelope signals were used to calculate the decorrelation pattern. The results were compared to the mean decorrelation pattern for plug blood-flow. The RF signals decorrelation patterns were in good agreement with those obtained for plug blood flow. Envelope decorrelation patterns show a close agreement with the one for plug blood flow. For axial blood flow, there is a discrepancy between decorrelation patterns. The results presented here suggest that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow probably will not be affected by different transverse blood-flow conditions     

半导体激光器恒温控制系统的高精度温度测量研究

半导体激光器性能受温度影响较大,为了提高其工作稳定性,设计了一个应用于半导体激光器的恒温控制系统.该系统由0.5 mA恒流源对Pt100温度传感器供电,采用四线制测量方法获得精确的温度信号.应用TLC2652斩波放大器设计前置放大器,并采用差分放大电路对信号进行后续比较放大.使用半导体制冷器(TEC)制冷,实现系统的恒温控制.经实验数据分析可以看出,该恒温系统可有效地工作,温度控制偏差最大为±0.02℃.通过调节相应参数,可自由设定恒温系统的温度值,应用于不同温度控制环境.     

Flux flow velocity in superconducting films by measurement of passage time

The velocity of flux tubes in thin superconducting films has been determined by measuring the time for their passing across the film. A legion of flux tubes has been pulsed in on the left side of a film carrying a current large enough to break the pinning. The arrival of the flux tubes on the right side is observed with a pick-up coil. Flow velocities of 3 to 50×10⁴ cm/sec have been observed with current densities up to 10⁵ A/cm².Supported in part by the National Science Foundation, in part by the Cryogenics Center through a grant from the DOD Themis program.     

编码超声血流多深度检测

血流信息检测及其成像因其独特的优势,在临床上得到广泛应用。但常规经颅多普勒超声系统仍采用模拟和数字电路结合的传统技术,这类系统容易受到外界干扰且不能进行多深度检测。文章设计出一种全数字多普勒超声血流检测系统方案,弥补了传统模拟系统存在的问题。多普勒仿体和人体实验结果表明,该系统能够进行多深度检测,确定血管的深度;同时,还提高了检测灵敏度、超声穿透力和系统成像分辨率。     

利用超声多普勒技术测量低速血流

利用常规的多普勒系统较难进行低速血流的测量,本文在讨论了常规的多普勒系统的局限后,就一种可测量低速血流的超声多普勒技术的原理,方法进行讨论,并通过计算机模拟实验实现了这种方法。     

Maximum likelihood blood velocity estimator incorporating properties of flow physics

The aspect of correlation among the blood velocities in time and space has not received much attention in previous blood velocity estimators. The theory of fluid mechanics predicts this property of the blood flow. Additionally, most estimators based on a cross-correlation analysis are limited on the maximum velocity detectable. This is due to the occurrence of multiple peaks in the cross-correlation function. In this study a new estimator (CMLE), which is based on correlation (C) properties inherited from fluid flow and maximum likelihood estimation (MLE), is derived and evaluated on a set of simulated and in vivo data from the carotid artery. The estimator is meant for two-dimensional (2-D) color flow imaging. The resulting mathematical relation for the estimator consists of two terms. The first term performs a cross-correlation analysis on the signal segment in the radio frequency (RF)-data under investigation. The flow physic properties are exploited in the second term, as the range of velocity values investigated in the cross-correlation analysis are compared to the velocity estimates in the temporal and spatial neighborhood of the signal segment under investigation. The new estimator has been compared to the cross-correlation (CC) estimator and the previously developed maximum likelihood estimator (MLE). The results show that the CMLE can handle a larger velocity search range and is capable of estimating even low velocity levels from tissue motion. The CC and the MLE produce incorrect velocity estimates due to the multiple peaks, when the velocity search range is increased above the maximum detectable velocity. The root-mean square error (RMS) on the velocity estimates for the simulated data is on the order of 7 cm/s (14%) for the CMLE, and it is comparable to the RMS for the CC and the MLE. When the velocity search range is set to twice the limit of the CC and the MLE, the number of incorrect velocity estimates are 0, 19.1, and 7.2% for the CMLE, CC, and MLE, respectively. The ability to handle a larger search range and estimating low velocity levels was confirmed on in vivo data.     

Lateral blood flow velocity estimation based on ultrasound speckle size change with scan velocity

Conventional (Doppler-based) blood flow velocity measurement methods using ultrasound are capable of resolving the axial component (i.e., that aligned with the ultrasound propagation direction) of the blood flow velocity vector. However, these methods are incapable of detecting blood flow in the direction normal to the ultrasound beam. In addition, these methods require repeated pulse-echo interrogation at the same spatial location. A new method has been introduced which estimates the lateral component of blood flow within a single image frame using the observation that the speckle pattern corresponding to blood reflectors (typically red blood cells) stretches (i.e., is smeared) if the blood is moving in the same direction as the electronically-controlled transducer line selection in a 2-D image. The situation is analogous to the observed distortion of a subject photographed with a moving camera. The results of previous research showed a linear relationship between the stretch factor (increase in lateral speckle size) and blood flow velocity. However, errors exist in the estimation when used to measure blood flow velocity. In this paper, the relationship between speckle size and blood flow velocity is investigated further with both simulated flow data and measurements from a blood flow phantom. It can be seen that: 1) when the blood flow velocity is much greater than the scan velocity (spatial rate of A-line acquisition), the velocity will be significantly underestimated because of speckle decorrelation caused by quick blood movement out of the ultrasound beam; 2) modeled flow gradients increase the average estimation error from a range between 1.4% and 4.4%, to a range between 4.4% and 6.8%; and 3) estimation performance in a blood flow phantom with both flow gradients and random motion of scatterers increases the average estimation error to between 6.1% and 7.8%. Initial attempts at a multiple-scan strategy for estimating flow by a least-squares model suggest the possibility of increased accuracy using multiple scan velocities.     

Self-mixing laser speckle velocimeter for blood flow measurement

A velocimeter using speckle phenomena in self-mixing laser diodes (SM-LDs) is used to evaluate the blood flow noninvasively. The mean frequency of the speckle signal obtained from the self-mixing laser diode reflects the activity of the blood flow in a certain probing area. The experimental results show that this new type of speckle velocimeter can be useful for the relative evaluation of blood flow in human tissues     

电磁流量计在水厂流量测量中的应用

首先介绍电磁流量计在水厂流量测量中的应用,然后简述电磁流量计的测量原理、优点;根据性能价格比选择流量计;从安装、环境条件和流体特性等方面,论述它在安装调试、运行期的故障。最后介绍清洗探头、防雷电,抗干扰等措施的解决方法。     

半导体激光器在实时测温系统中的应用

该论文介绍了一种利用半导体激光器InGaAs I作光源 ,使用钽酸锂热释电探测器作光接收器件 ,以单片机为核心实现的中、高温度实时测量系统。该系统主要由光发射与接收系统、信号放大与处理系统及显示系统三部分组成。     

Phase reconstruction of modulated ultrasonic signals and new measurement technique of flow velocity

Streaming fluid modulates the ultrasound as well in phase as in amplitude. The complex bandpass sampling separates the phase and the amplitude information. Because of unknown zero phase adjustment point of the receiving sensor, the demodulated phase signal has to be reconstructed. The reconstruction is based on the analysis of the density distribution function of the phase angle. To determine the transit time of the structures between two ultrasonic barriers two methods can be used. The maximum of the cross-correlation function corresponds to the transit time. The other way is to add the demodulated signal of both barriers. In the spectrum of the added signals after a filtering a cosine function can be determined. The frequency of this function is directly proportional to the transit time.     

Combined velocity,size, and concentration measurement for particles in a two-phase flow

Translated from Izmeritel'naya Tekhnika, No. 9, pp. 40–42, September, 1991.     

Simultaneous measurement of the stagnation temperature and specific mass flow rate in a hypersonic gas flow

The procedure and results of simultaneous measurement of the stagnation temperature and specific mass flow of gas in a hypersonic flow by means of heated-chamber impact tubes is discussed. The construction of the tubes is described.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 5, pp. 759–766, November, 1982.     

Interpolation methods for time-delay estimation using cross-correlation method for blood velocity measurement

The cross-correlation method (CCM) for blood flow velocity measurement using Doppler ultrasound is based on time delay estimation of echoes from pulse-to-pulse. The sampling frequency of the received signal is usually kept as low as possible in order to reduce computational complexity, and the peak in the correlation function is found by interpolating the correlation function. The parabolic-fit interpolation method introduces a bias at low sampling rate to the ultrasound center frequency ratio. In this study, four different methods are suggested to improve the estimation accuracy: (1) Parabolic interpolation with bias-compensation, derived from a theoretical signal model. (2) Parabolic interpolation combined with linear filter interpolation of the correlation function. (3) Parabolic interpolation to the complex correlation function envelope. (4) Matched filter interpolation applied to the correlation function. The new interpolation methods are analyzed both by computer simulated signals and RF-signals recorded from a patient with time delay larger than 1/f(0), where f(0) is the center frequency. The simulation results show that these methods are more accurate than the parabolic-fit method. From the simulation, the worst estimation accuracy is about 1.25% of 1/f(0) for the parabolic-fit interpolation, and it is improved by the above methods to less than 0.5% of 1/f(0) when the sampling rate is 10 MHz, the center frequency is 2.5 MHz and the bandwidth is 1 MHz. This improvement also can be observed in the experimental data. Furthermore, the matched filter interpolation gives the best performance when signal-to-noise ratio (SNR) is low. This is verified both by simulation and experimentation.     

Shape recovery of an optically trapped vesicle: effect of flow velocity and temperature

A new biophysical approach based on optical tweezers is developed to measure the time-dependent shape transformation and recovery of a single liposome, which is induced by the sudden stop of a moving liposome from various flow velocities at constant temperature. A simple viscoelastic model has been applied to correlate the temporal geometric parameter of the deformed liposome with a characteristic time constant, i.e., the ratio of membrane viscosity to elasticity. Our results show that membrane viscosity becomes dominant in governing the shape recovery rate when sample temperature goes beyond the main phase transition temperature of the phospholipid bilayer. More importantly, flow speed and vesicle size are demonstrated as key physical determinants for the shape recovery of liposome.     

On the problem of construction of the underground contour of water-development works with portions of constant flow velocity

The underground contour of a sunk rectangular apron whose angles are rounded off by the curves of constant filtration rate is constructed in the case where the water-permeable base is underlain by a confining layer with a curvilinear roof, characterized by a constant flow velocity, too. The corresponding boundary-value problem is solved by a semiinverse application of the velocity-hodograph method. The cases of the apron with a horizontal insert in flow and the rabbet in flow are studied in detail. The results of numerical calculations are given; the influence of the physical parameters of the model on the shape and dimensions of the underground contour of the dam is analyzed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 826–833, September–October, 2008.     

Direct measurement of tissue blood flow and metabolism with diffuse optics

Diffuse optics has proven useful for quantitative assessment of tissue oxy- and deoxyhaemoglobin concentrations and, more recently, for measurement of microvascular blood flow. In this paper, we focus on the flow monitoring technique: diffuse correlation spectroscopy (DCS). Representative clinical and pre-clinical studies from our laboratory illustrate the potential of DCS. Validation of DCS blood flow indices in human brain and muscle is presented. Comparison of DCS with arterial spin-labelled MRI, xenon-CT and Doppler ultrasound shows good agreement (0.50相似文献