共查询到18条相似文献,搜索用时 140 毫秒
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为了解决医学超声成像系统中面临的采样率高,数据量大的问题,提出将压缩感知理论方法用于医学超声成像。首先建立了超声信号在时域的稀疏表达模型,然后利用模拟信息转换器对信号进行稀疏采样,最后使用最优化方法完成回波信号重建,利用合成发射孔径方式完成最终超声成像。为了验证算法的有效性,利用Field II对点目标以及复杂组织目标进行了仿真实验,在均方误差、分辨率、对比度以及成像质量上与常规成像结果对比分析。结果表明,采用1/2奈奎斯特采样频率,以30%原始数据所完成的成像仍然可保证良好的图像质量。采用压缩感知理论可以大幅度降低医学超声系统的采样率及总数据量。 相似文献
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为解决混凝土结构中分层缺陷的在线非接触检测难题,论文提出了利用空气耦合(简称:空耦)超声导波定量检测混凝土结构中分层缺陷的新方法。首先研究了空耦超声导波在混凝土结构中的传播特性,理论分析和实验表明,利用空耦超声波以入射角8.7°入射厚度为50 mm的混凝土板时,可以激发以A0模态为主的导波。然后构建了空耦超声导波扫查实验系统,在混凝土结构单侧利用一对倾斜8.7°的空耦探头激励和接收导波信号,通过分析发现A0模态对分层缺陷敏感,且其幅度与扫查路径中的分层缺陷尺寸存在单调变化关系;在此基础上,对检测区域进行扫查,利用不同位置处的导波信号幅度实现分层缺陷的二维成像。实验结果表明,该方法不仅可以避免耦合剂对检测结果的影响,同时可实现对服役状态下混凝土结构中分层位置及尺寸的定量检测。 相似文献
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医学图像信息数字化及其计算机处理技术从根本上改变了传统的医学图像采集、显示、存储和传输的模式,为医学诊断、临床治疗以及医学研究提供了精确的医学图像信息.探讨一种可以实现医学图像的自动获取、存储、显示、分析、传输和管理的小型超声工作站系统.讨论通过A/D转换和信号滤波将模拟信号数字化,通过Windows操作系统的API调用,实现超声诊断的图文数字化管理. 相似文献
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随着科技的发展,工业上对工件和材料的要求越来越高,对作为无损检测重要分支的超声检测技术的检测效率和检测精度提出了更高的要求。本文基于超声卡和高速采集卡设计了一种超声检测系统。硬件系统是通过超声卡发射超声信号,使用AD采样,利用PCI总线进行传输;软件系统基于VC6.0软件平台设计上位机程序。最后系统对标准件进行实验,结果表明本文设计的系统能够准确显示工件的超声信号和保存数据,并在相关项目上已经得到了良好应用。 相似文献
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Huang CC Lee PY Chen PY Liu TY 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(1):182-188
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. 相似文献
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Bashford G.R. von Ramm O.T. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(3):376-384
This article describes a new angle-independent method suitable for three-dimensional (3-D) blood flow velocity measurement that tracks features of the ultrasonic speckle produced by a pulse echo system. In this method, a feature is identified and followed over time to detect motion. Other blood flow velocity measurement methods typically estimate velocity using one- (1-D) or two-dimensional (2-D) spatial and time information. Speckle decorrelation due to motion in the elevation dimension may hinder this estimate of the true 3-D blood flow velocity vector. Feature tracking is a 3-D method with the ability to measure the true blood velocity vector rather than a projection onto a line or plane. Off-line experiments using a tissue phantom and a real-time volumetric ultrasound imaging system have shown that the local maximum detected value of the speckle signal may be identified and tracked for measuring velocities typical of human blood flow. The limitations of feature tracking, including the uncertainty of the peak location and the duration of the local maxima are discussed. An analysis of the expected error using this method is given 相似文献
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Nikolov SI Jensen JA 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(7):848-856
A new method for acquiring flow images using synthetic aperture techniques in medical ultrasound is presented. The new approach makes it possible to have a continuous acquisition of flow data throughout the whole image simultaneously, and this can significantly improve blood velocity estimation. Any type of filter can be used for discrimination between tissue and blood flow without initialization, and the number of lines used for velocity estimation is limited only by the nonstationarity of the flow. The new approach is investigated through both simulations and measurements. A flow rig is used for generating a parabolic laminar flow, and a research scanner is used for acquiring RF data from individual transducer elements. A reference profile is calculated from a mass flow meter. The parabolic velocity profile is estimated using the new approach with a relative standard deviation of 2.2% and a mean relative bias of 3.4% using 24 pulse emissions at a flow angle of 45 degrees. The 24 emissions can be used for making a full-color flow map image. An in-vivo image of flow in the carotid artery for a 29-year-old male also is presented. The full image is acquired using 24 emissions. 相似文献
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Lupotti FA van der Steen AF Mastik F de Korte CL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(6):705-714
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 相似文献
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Tortoli P Andreuccetti F Manes G Atzeni C 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(5):545-551
Multigate operation of an ultrasound pulsed Doppler flowmeter, providing Doppler frequency detection in a number of adjacent sample volumes, is capable of displaying the instantaneous blood velocity distribution along the cross section of a sonified vessel. Real-time serial Doppler processing of 32 range cells has been implemented in a novel system using fast spectral analysis based on surface-acoustic wave (SAW) dispersive filters. The basic architecture and first in vitro experiments were reported previously. The in vivo application of the system is described here, and images of human carotid artery and jugular vein are presented. Appropriate display formats are introduced to use the great amount of information known on spatial and temporal behavior of flow profiles. Digital postprocessing of spectral Doppler data allows velocity profiles to be displayed at selected times to correlate spatial and temporal evolution. A color code can be used to represent different velocity strengths. The potential application of the system to two-dimensional (2-D) flow imaging is discussed. 相似文献
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Yeh CK Lu SY Chen YS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(1):74-83
To improve the resolution of contrast-assisted imaging systems, we previously developed a 25-MHz microbubbles-destruction/replenishment imaging system with a spatial resolution of 160 X 160 microm. The goal of the present study was to propose a new approach for functionally evaluating the microvascular volumetric blood flow based on this high-frequency, ultrasound imaging system. The approach includes locating the perfusion area and estimating the blood flow velocity therein. Because the correlation changes between before and after microbubble destruction in two adjacent images, a correlated-based approach was introduced to detect the blood perfusion area. We also have derived a new sigmoid-based model for characterizing the microbubbles replenishment process. Two parameters derived from the sigmoid-based model - the rate constant and inflection time - were adopted to evaluate the blood flow velocity. This model was validated using both simulations and in vitro experiments for mean flow velocities ranging from 1 to 10 mm/s, which showed that the model was in good agreement with simulated and measured microbubble-replenishment time-intensity curves. The results indicate that the actual flow velocity is highly correlated with the estimates of the rate constant and the reciprocal of the inflection time. B-mode imaging experiments for mean flow velocities ranging from 0.4 to 2.1 mm/s were used to assess the volumetric flow in the microcirculation. The results indicated the high correlation between the actual volumetric flow rate and the product of the estimated perfusion area and rate constant, and the reciprocal of the inflection time. We also found that the boundary of the microbubble destruction volume significantly affected estimations of the flow velocity. The perfusion area can be located, and the corresponding flow velocity can be estimated simultaneously in a one-stage, microbubble-destruction/replenishment process, which makes the assessment of the volumetric bloo- d flow in the microcirculation feasible using a real-time, high-frequency ultrasound system. 相似文献
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Xu T Bashford GR 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2010,57(12):2695-2703
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. 相似文献
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3-D flow velocity vector estimation with a triple-beam lens transducer-experimental results 总被引:2,自引:0,他引:2
Current commercial ultrasound blood flow measurement systems only measure the axial component of the true blood flow velocity vector. In order to overcome this limitation, a technique which tracks blood cell scatterers as they move between three ultrasound beams has been developed. With this technique, the entire 3-D blood flow velocity vector can be estimated. Previous work has presented the theory behind the technique, lens transducer design and construction, as well as results of computer simulations and preliminary experimental results. This work presents the first experimental results obtained with a prototype system for continuous, fully developed flow in a flow phantom under a wide range of flow rates and flow directions. The results indicate that the accurate measurement of the 3-D flow velocity vector using this technique is possible. 相似文献