基于超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。     

基于超声造影剂的低速血流多普勒测量技术

本文研究了以超声造影剂为基础的低速血流基波和谱波多普勒测量技术的基本原理,讨论了基于造影剂的多普勒方法的可测低速血流的下降问题,并建立造影基波／谐波多普勒测量实验系统,对自制白蛋白包膜超声造影剂产生的基波及谐波多普勒进行研究,并通过模拟血管血流信号,对比研究基波和谐波多普勒方法在强干扰情况下对低速血流的检测能力。研究表明：造影基波多普勒方法不能从根本上解决组织运动杂波干扰问题,而谐波多普勒技术可测     

超分辨率图像重建方法及其在超声图像中的应用

采用时域模型实现基于多帧图像的超分辨率图像重建方法.方法的步骤为先对多帧图像进行光流场配准,用基于最速下降的最大似然估计法重建超分辨率的图像,并对重建的图像进行基于维纳滤波的降噪.在模拟实验中,给定一幅高分辨率源图像,模拟成像过程获取具有亚像素平动的低分辨率加噪图像序列,然后利用上述方法重建超分辨率图像.对标准数字图像进行模拟实验,结果表明该重建方法具有良好的效果.对超声图像的处理结果也表明该方法能有效提高超声图像的分辨率,有望为超声图像分辨率增强提供一种新的手段.     

超声技术在心血管疾病诊治及研究中的应用

介绍超声技术在心血管疾病诊治及研究中的应用与进展。血流介导的血管扩张功能检测与二维斑点追踪成像有助于早期诊断心血管疾病,高频率超声成像与有创超声血流、位移测量技术在心血管研究领域发挥着重要作用。     

图像融合在医学超声影像中的应用

图像融合是图像分析和处理的基本问题,在医学影像领域有着广泛的应用。将它引入医学超声影像中,以期获得更清晰的利于诊断的医学超声图像。利用小波变换理论首先将谐波图像与基波图像进行分解,然后利用基于窗口的融合规则进行融合,最后利用小波逆变换重建图像。融合结果表明融合后的医学超声图像更清晰,计算结果表明信噪比更高。融合方法使得借助超声进行疾病诊断的结果更为准确。     

三维超声成像在乳腺肿块诊断中应用价值

目的探讨三维超声成像技术对乳腺肿块的诊断价值。方法以我院2010年1月~2012年6月收治的60例女性患者为研究对象,所有患者均行二维、三维超声检查,对比2种检查方式的诊断准确率及检出率。结果超声诊断结果与手术及穿刺病理结果进行对照,60例患者共71个肿块。二维超声对59个乳腺肿块诊断正确,诊断准确率为83.1%(59/71),三维超声对68个乳腺肿块诊断正确,诊断准确率为95.8%(68/71),三维超声诊断准确率率高于二维超声,差异有统计学意义(P<0.05)。二维超声血流检出率63.41%(26/41),三维超声血流检出率97.56%(40/41),三维超声血流检出率高于二维超声血流检出率,差异有统计学意义(P<0.05)。结论三维超声诊断乳腺肿块准确率和血流检出率高于二维超声,使用三维超声可提高乳腺肿块鉴别诊断水平。     

超声彩色血流成像中基于动态区域划分抑制杂波的方法

为提高超声彩色血流成像质量,提出了一种基于动态区域划分的杂波抑制方法。先根据超声回波信号的幅度对血流与组织区域作出初步的划分,再根据杂波运动的非平稳性对组织区域作进一步的调整,最后对各区域用特征向量滤波器进行杂波抑制。将本方法用于计算机仿真血流信号和人体实测血流数据,结果表明:本方法在有效抑制非平稳杂波的同时,能较好地保持血流流速剖面的完整性,解决了传统均匀分段特征向量滤波器选取区间长度时的矛盾,有望成为超声彩色血流成像中一种有效的杂波抑制方法。     

基于准三维超声成像的电阻点焊定量检测技术研究

针对利用传统超声C扫成像方法对电阻点焊定量检测时图像对比度分辨率低的问题,对超声波在被测构件中传播时表现出的衰减特性进行了研究,分析了电阻点焊超声信号的特征,测定了超声检测信号在被测工件中的衰减系数,提出了一种准三维电阻点焊超声成像方法。该方法基于小波多子带差异性补偿算法,同时对超声波传播的距离和频率进行了补偿,在减小超声波衰减的同时也提高了电阻点焊超声图像的对比度分辨率。利用该方法开展了电阻点焊相关参数的定量化检测研究,并进行了相关的实验验证。研究结果表明,该技术有效提高了电阻点焊超声成像的对比度分辨率,可以避免图像中目标检测对象与背景的融合现象,提高了电阻点焊参数的定量化检测能力,并可将检测结果友好表征。     

PIV在二维大应变变形现象研究中的应用

切削加工可作为研究大应变变形现象和细化金属与合金微观组织的实验手段,其关键技术之一是测量第一变形区和第二变形区（刀一屑接触面）的变形区域特征,如材料的流速、应变、应变率和温度等。粒子图像测速（PIV）是一种基于流场图像互相关分析的二维流场非接触式测试技术。应用PIV技术,可获得第一变形区和刀一屑接触面的高速图像序列,从而得到这些区域材料的流速、应变和应变速率分布。     

用于超声散斑跟踪血流测速的多角度平面波局部运动补偿

血流速度剖面用于计算壁面剪切率等血流动力学指标,与动脉粥样硬化病程发展密切相关。 超快超声散斑跟踪广泛用 于血流速度剖面估计,然而多角度平面波复合成像存在血流散射体的运动伪影,不利于流速估计。 提出了一种多角度平面波复 合成像的局部运动补偿法,对射频信号时间序列的相邻帧进行局部运动补偿来消除不同径向位置的运动伪影,从而提高流速测 量准确性。 相比直接相干复合,B-MoCo 法将仿真、仿体实验中流速测量结果的归一化均方根误差平均减小了 10. 37% 、 37. 82% ,说明了 B-MoCo 法的有效性。 基于兔骼动脉的实测实验进一步证明了 B-MoCo 法的临床可行性。 综上,B-MoCo 法能够 有效提高血流速度剖面的测量精度,有助于相关心血管疾病的早期诊断与病程监测。     

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.     

Blood flow: insights from ultrasound

Ultrasonic pulse-echo systems can provide range-finding, time-position and real-time two-dimensional images of soft-tissue structures within the body. The Doppler effect can be used to study motion and blood flow. Continuous wave Doppler instruments provide information about velocity and direction of flow; depth discrimination can be obtained by pulsing the ultrasound. Two-dimensional Doppler flow imaging can be achieved by manual scanning of a probe over the skin surface. The combination of real-time pulse-echo imaging with pulsed Doppler blood flow detection in the duplex scanner makes it possible to localize the anatomical position of the Doppler sample volume. Real-time Doppler colour flow imaging combines traditional ultrasonic scanning with a two-dimensional flow map. Using appropriate ultrasonic instruments, blood flow volume rates, blood flow velocity profiles, pressure gradients, orifice areas, flow disturbances, jets, characteristics of blood vessels and the circulatory system, and tissue perfusion can all be investigated. These investigations have clinical applications in the study of cardiac, cerebral and peripheral blood flow, blood flow in the female pelvis, the fetus, the abdomen, the neonate, and in malignant tumours. Contemporary ultrasonic diagnosis employs exposure levels that are apparently free from biological risk, but other factors need to be taken into account in considering the prudent use of ultrasonic methods. Promising research is being carried out into the mechanism of ultrasonic scattering by blood, Doppler speckle, time-domain processing for blood flow imaging, methods for increasing the scanning speed, Doppler flow microscopy and contrast agents. The new technology that will result from this research should lead to further substantial progress in ultrasonic blood flow studies.     

Spectral Method of Detection of Laser Doppler Velocimeter Signals in Turbulent Flows

A spectral method of detection of laser Doppler velocimeter signals in turbulent flows is proposed. The method is based on estimating the signal/noise ratio adapted to the width of the power spectral density of the signal and comparing its value with the recognition threshold. Numerical simulations show that the error of the signal/noise ratio estimates is 1% for different velocities of the turbulent flow. Physical experiments aimed at measuring turbulent aerodynamic processes show that the proposed method offers a possibility of eliminating the errors of calculating the mean value and the velocity deviation equal to 15 and 78% by means of eliminating the signals with low signal/noise ratios from the processing system. Application of the proposed method also ensures lower nonuniformity of the signal/noise ratio estimates than that ensured by the famous method developed by Tropea for a wide range of turbulent velocities.     

一种基于NSCT变换的超声图像降噪新算法

为有效抑制超声仪器成像中固有的斑点噪声,提出了一种基于非降采样Contourlet变换(nonsubsampled Contourlettransform,NSCT)域中边缘信号系数区提取和最小均方误差(minimum mean square error,MMSE)估计的超声图像的降噪算法。根据NSCT变换的细节信息刻画能力和平移不变性,对其各高频子带中系数进行分类,提取出边缘信号和平缓信号系数区;对超声图像的乘性斑点噪声进行推导研究,在边缘信号系数区和平缓信号系数区,根据各自噪声项的性质分别得出满足贝叶斯最小均方误差估计的降噪滤波方程;最后,对降噪后的系数进行NSCT反变换重建得到降噪图像。仿真图像和临床超声图像的实验结果证实,该算法与传统方法相比,不但能更有效地对斑点噪声进行抑制,也更好地保留了图像的细节信息。     

Denoising and despiking ADV velocity and salinity concentration data in turbulent stratified flows

Due to the presence of noise and spikes in velocity measurements of turbulent flow fields, understanding the flow pattern may be seriously affected by the spurious values for zones where certain flow behaviour is not necessarily expected. In a series of laboratory experiments the velocity data recorded, using Acoustic Doppler Velocity meters (ADVs), and the salinity measurements were noticeably noisy. In despiking and denoising the velocity data a linear correlation algorithm was established, which successfully lowered the noise levels and removed the spikes. For the assessment of the method, an autoregressive model was used to generate a clean velocity signal. The spikes were generated with a uniformly random time index and a Gaussian distributed value, where White Gaussian noise was added to this simulated signal. Assessment was also undertaken on the signals generated using a three-dimensional numerical model. To enhance the comprehension of the flow field, an interpolation method for producing the missing data has also been developed, which may be deployed to increase the sampling frequency, or to produce data for the spatial domain at locations which are not included in the measurements. For salinity a different strategy was applied where a moving average procedure was carried out, as the data did not suffer from spikes and exhibited almost a constant band of noisy fluctuations.     

光寻址电位传感器的噪声分析与信号处理方法研究

鉴于光寻址电位传感器(LAPS)的响应信号较弱,传统的抽取频域基波分量的方法易受信号漂移和随机噪声的影响,提出了一种基于频域分量均方根和卡尔曼滤波的两步信号处理方法。基于光寻址电位传感器件的理论模型构建了其等效电路模型,推导得到输出信号的表达式,分析了漂移与噪声产生的原因及其抑制方法。通过实验检测了不同pH值的溶液,并采集了系统输出的光电流信号。求取信号傅里叶变换后频域中的基波分量、二次谐波分量、三次谐波分量的谱线幅值的均方根,然后对归一化电流-偏压(I-V)特性曲线进行卡尔曼滤波。实验结果表明,相对于单纯抽取基波分量的方法,基于频域分量均方根和卡尔曼滤波的两步信号处理方法使检测结果的均方差(MSE)降低了97%,显著减少了信号漂移和随机噪声对检测结果的影响。     

Calibration procedure for performance evaluation of clinical Pulsed Doppler Systems

This paper describes the analysis of an experimental setup for the performances evaluation of Pulsed Doppler feature in clinical ultrasound scanners. The equipment basically consist on a commercial flow phantom made by a straight tube having a known and constant cross sectional area in which a blood mimicking fluid is forced to flow at laminar conditions. Given the accuracy declared by the manufacturer (±0.7 cm/s), unsatisfactory for low flow rates, we calibrated the phantom using the gravimetric method. From the digitized images of the Pulsed Doppler spectra over time, the mean velocities have been computed with the software package developed by the authors. Moreover, to test the calibration procedure in effective conditions, we carried out performance test on five different ultrasound platforms, equipped with phased array and convex array probes with a nominal mean velocity of the blood mimicking fluid ranging from 1.1 cm/s to 12.7 cm/s. The pooled data showed an overestimation of the mean velocity, from over 200% down to about 50%, depending on nominal flow rate and ultrasound equipment. The same data, corrected via the calibration curve, showed a sensible recovery of the estimated accuracy of the tested platforms at low flow rates (<3 cm/s).     

Ultrasound flow mapping of complex liquid metal flows with spatial self-calibration

Investigating the complex interaction of electrically conductive fluids and magnetic fields is relevant for a variety of applications from basic research in magnetohydrodynamics (MHD) to modeling of industrial processes involving metal melts, such as steel casting and crystal growth. However, experimental studies in this field are often limited by the performance of flow instrumentation for opaque liquids. Commercially available measurement systems usually lack the ability to provide a time-resolved imaging of transient flow structures. We present an ultrasound array Doppler velocimeter (UADV) for flow mapping in opaque liquids near room temperature. It is modular and flexible regarding its measurement configuration, for instance it allows capturing two velocity components in two planes (2d–2c) of 67×67 mm² with a frame rate of 30 Hz. It uses up to 9 linear arrays with 25 ultrasound transducers each driven in a parallelized time division multiplex (TDM) scheme. A FPGA-based signal processing allows a continuous realtime operation of the measurement system. Combining the single-component velocity data of each linear array to a 2d–2c flow field demands precise knowledge of the relative geometric position of the transducer arrays. We present a novel method that performs a spatial self-calibration by a mutual time of flight measurement, significantly reducing alignment errors. A measurement example of a magnetically stirred flow of GaInSn in a rectangular container is given. The UADV is applied to experiments in the context of manufacturing crystalline silicon ingots for photovoltaics.     

Online rheological measurement of dilute liquid-solid two-phase flow with ultrasound Doppler technique

An online and non-invasive ultrasound Doppler based rheometric method is proposed to measure the flow parameters in a dilute liquid-solid two-phase flow and analyze its rheological behaviours. The flow rate is obtained by integrating the ultrasound Doppler velocity profiles through annuluses formed across the cross-sectional area of the pipe while the pressure drop is calculated by choosing suitable models that captures the working conditions of quasi-homogeneous and heterogeneous dilute liquid-solid flows. Wall shear rate and wall shear stress are obtained from the above measurements with the rheological measurement models established. An experimental platform is built to form polystyrene-water and sand-water liquid-solid two-phase fluids for tests. The proposed method has mean absolute errors of 2.53% and 3.49% in flow rate measurement and 3.67% and 5.87% in pressure measurement for polystyrene-water and sand-water fluids, respectively. The experimental results have shown that the rheological characteristics of both fluids fit well with the power law fluid model.