多普勒血流信号最大频率曲线的特征分析及应用

文章主要研究从超声多普勒血流信号的最大频率曲线中提取特征值,并用于临床血管疾病诊断的方法。先利用短时傅里叶变换分析采样所得的音频多普勒血流信号,接着用百分比法得到信号的最大频率曲线,然后提取最大频率曲线频谱各峰值的比作为特征值,并将它们用于血管疾病的诊断。通过对颈动脉多普勒血流信号的临床分析表明：此方法比传统的声谱参数法有更高的诊断准确性。     

彩色多普勒超声对移植肾血管并发症的诊断价值

目的:彩色多普勒超声检查可较敏感地反映移植肾血流动力学的改变,随时观察移植肾的成活情况,评价彩色多普勒超声在移植肾血管并发症中的应用效果。方法:回顾性分析9例移植肾血管并发症患者的彩色多普勒超声结果,观察肾结构、肾内血流信号的分布、肾静脉主干回声和血流充盈情况,测量主肾动脉、段动脉、叶间动脉及弓形动脉流速及阻力指数、搏动指数。结果:对2007年9月-2012年9月10例移植肾血管并发症进行分析,5例肾动脉狭窄,1例肾动脉栓塞,1例肾静脉狭窄,2例肾静脉血栓及1例假性动脉瘤。结论:彩色多普勒超声具有简便、迅速、无创、可重复性等优点,已成为肾移植后临床观察治疗效果的首选监测手段。它能客观、动态显示移植肾形态结构及其内部的血流分布,血流频谱形态、流速、舒张期血流方向和血流指数变化,及时发现移植肾血管并发症,查找导致移植肾功能损害的部分原因,早期明确诊断并给予及时治疗,对提高肾移植成功率起重要作用。     

流量测量中超声多普勒信号的频谱特点及其与管道中流速的关系

研究了工业测流的超声多普勒信号的频谱特点，并以此为依据分析了不同安装方式对多普勒频谱的影响，提出了不同测量环境下，应用多普勒频谱计算流速的公式及必要的修正，为提高检测准确度提供了理论依据。     

几种超声NDE信号降噪方法的性能比较

为提高超声无损检测的准确性,需要对超声NDE信号中因随机分布于媒质中的大量散射微粒所引起的结构噪声进行降噪。由于信号和噪声的频谱范围基本重叠,传统的线性滤波方法不能提供理想的降噪结果。介绍了几种对超声NDE信号进行降噪的新方法:Wigner-Ville分布法、小波变换法和基于时间延迟的神经网络法,并从信噪比(SNR)、检测概率(PD)和估测深度(ED)等三个重要参数对它们的降噪性能进行计算机仿真实验的比较。结果表明:小波变换法和神经网络法的降噪效果较Wigner-Ville分布法要好。对实际信号的测试还表明,小波变换由于不像神经网络那样需要训练,是一种更为理想的超声NDE信号降噪方法。     

医学超声的新进展

近年来超声医学迅速发展。本文拟介绍超声诊断和超声治疗两个方面。超声诊断的研究工作特别活跃。自从１９８３年彩色多普勒血流成像技术首先用于心脏疾病诊断以来，８０年代末期对低流速的检测灵敏度大为提高，已广泛用于周围小血管和内脏血管的血流显示。但早期所用为频域范围内的自相关技术，流速过大（实际为：多普勒频移大于Ｎｙｑｕｉｓｔ频率）时发生混迭（ａｌｉａｓｉｎｇ）伪差。另一种为时域范围内的互相关技术，应用选通门、固定回声消除及回声群体波链的叠合等重要步骤，直接计算出散射体的流速。时域相关的彩色血流成像可消除…     

冠状动脉血管阻抗估计系统及其临床应用

利用PC机和图像、信号采集设备，建立冠状动脉血管阻抗的估计系统。该系统从血管内超声和血压检测仪器采集冠状动脉内的超声图像、血流多普勒和血压信号，通过提取管腔的截面积曲线和流速信息，获取血流量曲线。结合血压曲线，计算冠状动脉的等效阻抗。系统对不同程度冠脉狭窄、心肌架桥和微循环障碍病人进行临床应用，结果表明：血管阻抗可以反映血管供血和扩张能力与不同类型、程度病症间的关系，有望用于医学临床的辅助诊断。     

一种激光多普勒信号的频率估计算法

分析了激光多普勒回波信号的特征,提出了一种激光多普勒信号的频率估计算法.用FFT(Fast Fourier Transform)技术求得信号的自相关函数,并由功率谱得到信号频率的粗估计,然后用粗估计值对自相关函数移频,并根据移频信号自相关函数在一点的相位,估计频偏,对粗估计进行频率校正得到频率估计值.在进行信号频率粗估计和求相位时,利用计算过程中得到的结果和FFT因子的对称性,减少运算量.仿真结果表明,本算法有较小的均方根误差和平均绝对误差,应用于激光多普勒测速实验,结果与仿真一致.     

一种新的相位编码信号多普勒补偿算法研究

相位编码信号是一种多普勒频率敏感信号,而且码长越大,对多普勒频率越敏感,严重影响了雷达对高径向速度目标和远距离目标探测的能力。该文在分析伪码序列与多普勒容限关系的基础上,提出一种新的伪码调相准连续波雷达的多普勒补偿算法。该算法将回波信号取平方后送到动目标检测(MTD)滤波器中,通过提取回波信号中的多普勒频率信息,进行多普勒补偿。从仿真结果可以看出,该算法能够有效地降低多普勒频率对脉冲压缩结果的影响,验证了方法的可行性。     

超声多普勒信号平均频率估计方法的比较研究

本文介绍了一些常用的超声多谱勒信号平均频率估计法,并引入一种新的估计法：基于Teager算法的平均频率估计,然后分别对计算机模拟的多普勒信号和流速校刻系统的多普勒信号进行平均频率的估计和比较,给出了不同估计方法的优缺点和适用范围。     

密集频率数字信号的判定和校正方法

数字信号的频谱分析中,DFT只得到的频谱可以粗略确定实验信号各谐波频率,振幅和相位,单频谱谐波在其频率的某一邻域内的细化幅值频谱和相位频谱具有显著的特征,通过分析比较,单频率谐波细化频谱与矩形窗的频谱极其相似,依此为准绳,可以判定密集频率信号,进而通过待定谐波参数,选择合适的参数区间和步长组合循环计算,并用矩形窗频谱近似单频率谐波细化频谱的办法,则可以还原校正密集频率的谐波参数,校正精度略低于细化频谱对单频率谐波的计算结果,该方法可以较好的进行情况多变的多个密集频率频谱分析,越多的密集频谱,需要更大的计算量。     

In vivo measurement of blood flow in a micro‐scale stenosis model generated by laser photothermal blood coagulation

Blood flow in a stenosed vessel is one of the most important issues, because it is closely related to the outbreak of circulatory diseases. To overcome the technological limitations encountered in the haemodynamic studies using in vitro stenosis models, the authors induced a stenosed flow model in the extraembryonic vessels of a chicken embryo. Blood was coagulated by laser irradiation to artificially form a stenosis on the designated spot in a straight blood vessel. Owing to photothermal coagulation of red blood cells (RBCs), the blood is denatured and a stable blood coagulum is induced in the vessel. The blood coagulum adheres firmly and stably on the vessel wall without any size variation. It disturbs the on‐coming blood flow significantly. To investigate the haemodynamic characteristics of the blood flow in the stenosed vessel, a micro particle image velocimetry technique was employed using RBCs as tracers to measure the spatial distributions of velocity vectors, streamlines and shear rate. The present simple modelling of in vivo stenosis would be useful for investigating the basic haemodynamic mechanisms underlying circulatory vascular diseases.Inspec keywords: adhesion, biological effects of laser radiation, biomedical optical imaging, blood, blood flow measurement, blood vessels, cellular biophysics, coagulation, diseases, flow visualisation, laser applications in medicine, photothermal effects, shear flowOther keywords: in vivo measurement, blood flow, microscale stenosis model, laser photothermal blood coagulation, stenosed vessel, circulatory diseases, haemodynamics, extraembryonic vessels, chicken embryo, laser irradiation, blood vessel, red blood cells, blood coagulum, adherence, vessel wall, microparticle image velocimetry, shear rate, circulatory vascular diseasesInspec keywords: adhesion, biological effects of laser radiation, biomedical optical imaging, blood, blood flow measurement, blood vessels, cellular biophysics, coagulation, diseases, flow visualisation, laser applications in medicine, photothermal effects, shear flowOther keywords: in vivo measurement, blood flow, microscale stenosis model, laser photothermal blood coagulation, stenosed vessel, circulatory diseases, haemodynamics, extraembryonic vessels, chicken embryo, laser irradiation, blood vessel, red blood cells, blood coagulum, adherence, vessel wall, microparticle image velocimetry, shear rate, circulatory vascular diseases     

Pseudo-Wigner distribution for analysis of pulsed Dopplerultrasound

Existing pulsed Doppler ultrasound systems apply the spectrogram as a tool for analysis and display of signals scattered from the blood. The spectrogram is a time-frequency representation (TFR) of a signal that maps a one-dimensional signal of time into a two-dimensional function of time and frequency. The analysis of Doppler ultrasound signals requires application of a two-dimensional TFR rather than one-dimensional spectral representations due to the nonstationary nature of the signals scattered from blood. The classical spectrogram is a smoothed Wigner distribution (SWD) with a specific smoothing function. For this smoothing function, the smoothing, and hence the resolution in time and frequency, cannot be controlled independently. The purpose of this study is to examine the application of other SWD's to analysis and display of Doppler ultrasound signals. The present paper concentrates on the pseudo-Wigner distribution (PWD). The PWD and the spectrogram are examined and compared as analysis tools for nonstationary Doppler ultrasound signals. The performance of these two TFR's as a function of Doppler bandwidth is evaluated and compared for time-varying flow     

Doppler ultrasound spectral enhancement using the Gabor transform-based spectral subtraction

Most of the important clinical indices of blood flow are estimated from the spectrograms of Doppler ultrasound (US) signals. Any noise may degrade the readability of the spectrogram and the precision of the clinical indiCes, so the spectral enhancement plays an important role in Doppler US signal processing. A new Doppler US spectral enhancement method is proposed in this paper and implemented in three main steps: the Gabor transform is used to compute the Gabor coefficients of a Doppler US signal, the spectral subtraction is performed on the magnitude of the Gabor coefficients, and the Gabor expansion with the spectral subtracted Gabor coefficients is used to reconstruct the denoised Doppler US signal. The different analysis and synthesis windows are examined in the Gabor transform and expansion. The signal-to-noise ratio (SNR) improvement together with the overall enhancement of spectrograms are examined on the simulated Doppler US signals from a femoral artery. The results show the denoising method based on the orthogonal-like Gabor expansion achieves the best denoising performance. The experiments on some clinical Doppler US signals from umbilical arteries confirm the superior denoising performance of the new method.     

超声多普勒信号的频谱分析

超声多普勒信号具有非平稳性，利用传统的短时傅里叶变换分析该信号不能同时得到较高的时间频率精度，为克服这一缺点，本文简要介绍了多普勒信号频谱分析的几种新方法，并将它们和传统的方法进行性能的比较。     

血栓多普勒信号的多参数提取及分类

血栓的准确检测可以用于早期脑血管疾病的诊断，超声多普勒是一种无损的血栓检测技术。文章使用三种信号处理方法：传统的声谱分析法、小波分析法、renyi信息量分析法对血栓多普勒信号进行分析，提取出相应的特征参数，然后对敏感的特征参数采用反向传输(Back-Propagation，简称BP)神经网络进行分类，建立起血栓、干扰噪声和正常血流信号的自动判别系统。通过对300例仿真多普勒信号和163例临床采集的大脑中动脉多普勒信号进行分析，结果表明：本文建立的系统对血栓的检测率高于传统的方法，有望可用于血栓多普勒信号的自动检测。     

Doppler angle and flow velocity estimations using the classic and transverse Doppler effects

Current clinical Doppler ultrasound systems could only measure the flow vector parallel to the ultrasound beam axis, and the knowledge of the Doppler angle (beam-to-flow angle) is needed to calculate the real flow velocity. Currently, the Doppler angle is determined visually by manually aligning a vessel axis marker along the blood vessel on the duplex scan image of the ultrasound. The application of this procedure is often limited by practical constraints; therefore, measurements are not reliable. In order to overcome this problem, the authors developed a simple Doppler angle and flow velocity estimation method using a combination of the classic and transverse Doppler effects. This method uses only a single focused annular array transducer to estimate the Doppler angle and the flow velocity. The authors have verified experimentally that this method is successful for measuring constant flow in a flow phantom between 45 degrees and 80 degrees Doppler angle. The standard deviation of the estimated Doppler angles is less than 4.5 degrees . This method could be implemented easily in medical Doppler ultrasound systems to automatically estimate the Doppler angle and the flow velocity.     

Blood flow images by a SAW-based multigate Doppler system

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.     

利用正交相位法提取双向性血流的一种补偿方法

正交相位法是超声多普勒技术中提取双向性血流信息的一种重要方法。由于正交信号对之间通常存在幅度和相位的不平衡，从而导致了正、反血流信息的混淆，影响了平均频率，最大的估计和声谱图的正确显示，本文提出的补偿方法，让其中一个正交信号通过按一定要求设计的线性滤波器，从而得到幅度和相位基本平衡的正交信号对，提高了超声多普勒系统提取双向性血流的性能。