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。     

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。     

Isomorphism between pulsed-wave Doppler ultrasound anddirection-of-arrival estimation. I. Basic principles

Direction-of-arrival (DOA) estimation of signals is an important area of research in sonar and radar signal processing. Over the last few decades, numerous techniques have been developed for high-resolution DOA estimation. In this paper, we show that velocity measurement using pulsed-wave Doppler ultrasound and DOA estimation are isomorphic problems. We discuss a number of DOA methods and their potential application to flow velocity measurement using ultrasound. Wide-band DOA methods are of special interest because the pulses used for Doppler ultrasound are also wide band. These wide-band methods generally involve a preprocessing step to convert wideband signals to narrow band before applying high-resolution techniques. Application of DOA methods to Doppler ultrasound provides tools for high-resolution velocity measurement, identification of multiple velocity components within a sample volume, and clutter rejection     

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     

单边狭窄血管中超声多普勒信号的仿真研究

超声多普勒技术作为一种无损检测手段被广泛应用于血管狭窄的检测。以往的血管狭窄仿真信号的研究仅限于双边狭窄的对称情况,文章提出了一种单边狭窄血管中超声多普勒信号的仿真方法。首先用有限元分析方法(FEM)计算出狭窄血管中血流流速场分布情况,然后用总体分布非参数估计法计算出超声多普勒信号的功率谱密度(PSD),再用余弦叠加法获取仿真的超声多普勒时域信号。用快速傅里叶变换(FFT)计算仿真超声多普勒信号的频谱,从中计算最大频率、平均频率和频谱宽度等参数,分析它们在不同流速和狭窄程度下的特征,为血管疾病的诊断提供敏感的参数。     

Target velocity estimation with FM and PW echo ranging Doppler systems I. Signal analysis

The theoretical foundation is presented for velocity estimation with a pulsed wave (PW) Doppler system transmitting linear FM signals. The Doppler system possesses echo ranging capabilities and is evaluated in the context of Doppler ultrasound for blood velocity measurement. The FM excitation signal is formulated and the received signal is derived for a single moving particle. This signal is similar to the transmitted signal, but with modified parameters due to Doppler effect and range. The demodulated received signal is subsequently derived and analyzed. It is shown that, due to the Doppler effect, this is a linear sweep signal as well. The velocity and range information obtainable from one and two consecutively received signals are described. The latter case establishes the basis for an FM Doppler system for blood velocity measurements.     

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。     

频谱带宽和功率可变多普勒信号的计算机模拟

计算机模拟的多普勒信号，可以为各种多普勒信号处理方法的研究提供信号源，从而了解各种不同处理方法的性能。本文提出的方法，运用白噪声通过一时变滤波器的原理，模拟产生平均频率，带宽和功能均随时间变化的多普勒信号。     

Design and implementation of a smartphone-based portable ultrasound pulsed-wave Doppler device for blood flow measurement

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.     

Isomorphism between pulsed-wave Doppler ultrasound anddirection-of-arrival estimation. II. Experimental results

For pt. I see ibid., vol. 43, no. 5, p. 911-22 (1996). Pt. I presented the basic principles for applying high-resolution wide-band direction-of-arrival estimation techniques to pulsed-wave Doppler ultrasound. Such techniques provide high-resolution velocity profiles and enable the identification of multiple velocity components inside a sample volume. Another important application is the identification and rejection of wall clutter signals. A first and essential step in applying these techniques is to convert the wide-band echoes to narrow band. The 2D DFT projection method is used for this conversion. Two different narrow-band high-resolution methods are then applied to estimate the velocity distributions; the minimum variance (MV) and the multiple signal classification (MUSIC). Experimental results are presented to illustrate the potentials and limitations of applying wide-band DOA methods to different applications in pulsed-wave Doppler ultrasound     

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。     

Time-scale removal of "wall thump" in Doppler ultrasound signals: a simulation study

A novel approach for blood and wall signal separation in Doppler ultrasound is proposed in the wavelet time-scale domain. The Doppler signals of different clutter-to-blood ratios from a femoral artery were simulated and used in the experiments. Compared with the conventional high-pass filtering and the signal separation in the spectrogram, the new method delivers improved performance for "wall thump" removal with minimal loss of low-flow signal.     

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.     

一种基于残周期拟合的激光测冲击信号解调方法

针对激光干涉法冲击加速度校准中调频信号的数字化解调问题,提出一种基于残周期正弦波拟合的解调方法,使用约1/5周期的残周期正弦波模型进行滑动拟合,实现FM信号的数字化解调,对激光多普勒冲击信号波形具有良好的适应性,无需信号的截取等操作,拥有良好的算法稳定性和一个采样间隔的时间分辨力。在一组实际测量波形上的实验,验证了所述方法的正确性与可行性,为冲击加速度的计算提供了另外一种有效实用的数据处理方式。上述方法也可用于外差式激光干涉振动信号的解调。     

Implementation of a likelihood ratio test for laser Doppler velocimeter burst detection

A likelihood ratio test for laser Doppler velocimeter burst detection is derived and implemented with the appropriate photon detection statistics. This detector utilizes the first point of the autocorrelation function of the laser Doppler velocimeter photodetector signal and relies on a simple identity for this point. The detector looks at the ratio of two probability functions of the data (burst and no burst) to make its decision. Because the detector does not depend on the absolute strength of the signal, detection down to very low (-10-dB) signal-to-noise levels can be achieved. Because the autocorrelation function is insensitive to the phase of the signal, the detector will operate reliably with signals containing multiple overlapping bursts.     

Microembolic signal characterization using adaptive chirplet expansion

The adaptive chirplet expansion (ACE) is proposed to characterize high-intensity, transient signals from circulating microemboli. The nonnegative adaptive spectrogram based on the ACE gives a compact representation of the microembolic signal (MES) in joint-time, frequency domain. The mean instantaneous power (MIP) and mean instantaneous frequency (MIF) of MES are estimated from the adaptive spectrogram. Then, several important characteristics of MES, such as embolus-to-blood ratio (EBR), half width maximum (HWM), and embolic signal onset (ESO), are computed from the MIP, and the frequency modulation is examined in the MIF. To validate the new method, we improved the simulation model of the audio Doppler ultrasound signal. Some MESs together with a Doppler ultrasound signal from carotid blood flow are simulated in the simulation study. As a comparison, the adaptive Gabor expansion (AGE) also is implemented on these simulated signals. The experimental results of the simulation study show that the new method, based on the ACE, outperforms the AGE-based method in MES characterization. The consistent conclusion has been confirmed by the clinical study on some clinical MESs.     

A nonstationary signal simulation model for continuous wave and pulsed Doppler ultrasound

A computer simulation model of the nonstationary Doppler ultrasound signals arising from pulsatile blood flow is presented. The model uses sinusoidal components that are modulated by a power spectral density function that varies over the cardiac cycle. An empirical model consisting of two exponential functions is used to represent both the continuous wave and pulsed Doppler power spectral density for normal carotid arteries. It is shown that the spectrogram speckle patterns of the synthesized Doppler signals compare very well with those clinically recorded.     

冠脉内超声多普勒血流信号的极点特征

研究冠脉内超卢多普勒血流信号的极点特征，期望为微循环障碍等缺血性心脏病的诊断提供客观指标。先对冠脉内超声多普勒血流信号分段建立自回归滑动平均（Auto-regressive＆moving-average，即ARMA）模型，获取一个心动用期信号的极点分布，计算极点分布的特征参数。通过分析18例冠脉内超声多普勒血流信号，得出若干个对冠脉微循环障碍敏感的特征参数。结果表明：冠脉内超声多普勒血流信号的极点特征参数，可以一定程度反映冠脉循环的状况。     

Ultrafast compound Doppler imaging: providing full blood flow characterization

Doppler-based flow analysis methods require acquisition of ultrasound data at high spatio-temporal sampling rates. These rates represent a major technical challenge for ultrasound systems because a compromise between spatial and temporal resolution must be made in conventional approaches. Consequently, ultrasound scanners can either provide full quantitative Doppler information on a limited sample volume (spectral Doppler), or averaged Doppler velocity and/or power estimation on a large region of interest (Doppler flow imaging). In this work, we investigate a different strategy for acquiring Doppler information that can overcome the limitations of the existing Doppler modes by significantly reducing the required acquisition time. This technique is called ultrafast compound Doppler imaging and is based on the following concept: instead of successively insonifying the medium with focused beams, several tilted plane waves are sent into the medium and the backscattered signals are coherently summed to produce high-resolution ultrasound images. We demonstrate that this strategy allows reduction of the acquisition time by a factor of up to of 16 while keeping the same Doppler performance. Depending on the application, different directions to increase performance of Doppler analysis are proposed and the improvement is quantified: the ultrafast compound Doppler method allows faster acquisition frame rates for high-velocity flow imaging, or very high sensitivity for low-flow applications. Full quantitative Doppler flow analysis can be performed on a large region of interest, leading to much more information and improved functionality for the physician. By leveraging the recent emergence of ultrafast parallel beamforming systems, this paper demonstrates that breakthrough performances in flow analysis can be reached using this concept of ultrafast compound Doppler.     

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。