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     

Denoising quadrature Doppler signals from bi-directional flow using the wavelet frame

A novel approach was proposed to denoise quadrature Doppler signals from bi-directional blood flow using the wavelet frame and a soft-thresholding algorithm. A direction separation step was carried out first to avoid the phase distortion of quadrature Doppler signals, which is induced from the nonlinear, soft-thresholding processing. Then real parts of separated complex signals from the unidirectional flow were denoised independently. The quadrature Doppler signals from the bi-directional flow were reconstructed from the denoised separated signals. The approach has been applied to the simulated Doppler signals from a femoral artery. It is concluded from the experimental results that this method is practical for denoising quadrature Doppler signals.     

超声血流的无创伤检测和医学信号的特征提取

人体信号是随机性和背景噪声都很强的复杂信号。文章首先研究了利用超声Doppler技术定量检测血流速度的方法,然后将一些现代信息处理中的新理论、新方法引入医学超声的信息处理,为医学超声信息的特征提取提供了新的手段。这些理论包括：分形、数学形态学、数量化、小波变换、极点轨迹和血管传输线模型等。文章最后阐述了利用上述新方法作为技术核心而研制的三套应用系统;肺动脉血液动力学参数的无损估测系统、彩色编码的声谱系统和超声血流定量检测系统。     

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。     

便携式脐血流多普勒信号多参数分析系统

文章在笔记本计算机的硬件基础上建立了脐血流多普勒信号多参数分析的便携式系统。通过计算机声卡采集脐血流音频多普勒信号，然后进行传统的声谱参数分析、零极点模型分析、Teager算子分析和分形特征分析，应用Fisher多元判据法对四类特征参数进行分类决策，从而判断胎儿的生长情况。流速实验和临床试用的结果表明，该系统是有效的，可以应用于产科的临床诊断。     

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。     

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。     

Laser Doppler blood flow complementary metal oxide semiconductor imaging sensor with analog on-chip processing

A 4 x 4 pixel array with analog on-chip processing has been fabricated within a 0.35 mum complementary metal oxide semiconductor process as a prototype sensor for laser Doppler blood flow imaging. At each pixel the bandpass and frequency weighted filters necessary for processing laser Doppler blood flow signals have been designed and fabricated. Because of the space constraints of implementing an accurate omega(0.5) filter at the pixel level, this has been approximated using the "roll off" of a high-pass filter with a cutoff frequency set at 10 kHz. The sensor has been characterized using a modulated laser source. Fixed pattern noise is present that is demonstrated to be repeatable across the array and can be calibrated. Preliminary blood flow results on a finger before and after occlusion demonstrate that the sensor array provides the potential for a system that can be scaled to a larger number of pixels for blood flow imaging.     

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。     

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。     

Decorrelation characteristics of transverse blood flow along an intravascular array catheter

In recent years, a new method to measure transverse blood flow based on the decorrelation of radio frequency (RF) signals has been introduced. In this paper, we investigated the decorrelation characteristics of transverse blood flow measurement using an intravascular ultrasound (IVUS) array catheter 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 was measured. The correlation coefficient method was used to present the results. The decorrelation patterns for RF and for RF-envelope signals were studied. The decorrelation patterns from the RF signals were in good agreement with those obtained from theoretical beam profiles. This agreement suggests that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow can be assessed by measuring the ultrasound beam. A line of point scatterers, moved transversally across the acoustical beam (line spread function), can determine this decorrelation behaviour.     

A single FPGA-based portable ultrasound imaging system for point-of-care applications

We present a cost-effective portable ultrasound system based on a single field-programmable gate array (FPGA) for point-of-care applications. In the portable ultrasound system developed, all the ultrasound signal and image processing modules, including an effective 32-channel receive beamformer with pseudo-dynamic focusing, are embedded in an FPGA chip. For overall system control, a mobile processor running Linux at 667 MHz is used. The scan-converted ultrasound image data from the FPGA are directly transferred to the system controller via external direct memory access without a video processing unit. The potable ultrasound system developed can provide real-time B-mode imaging with a maximum frame rate of 30, and it has a battery life of approximately 1.5 h. These results indicate that the single FPGA-based portable ultrasound system developed is able to meet the processing requirements in medical ultrasound imaging while providing improved flexibility for adapting to emerging POC applications.     

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.     

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。     

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.     

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。     

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。     

面向包装物品的激光扫描测径系统设计

目的为适应包装物品测径的需求,设计面向包装物品的激光扫描测径系统。方法通过研究激光扫描技术在测距方面的应用,设计出适合包装物品测径需求的激光扫描测径系统装置,原理是将光源设计为可见激光,将包装防护的物品通过可见激光的测量扫描后,经过光电转换程序将光信号转化为电信号。转换后的电信号再经数据处理系统进行整理,得出准确结果,并在激光扫描测径系统中显示出来。结果该装置具有数字化的通信接口,与PC机连接组成智能化的包装物品测径装置,可对激光信号转化成电信号进行整理、分析和处理,并进行实时跟踪、监控,形成记录,如在包装物品扫描测径过程中出现意外时,能及时反馈给控制系统。结论该激光扫描测径系统实现了包装物品的全自动化、快速、精确测径,可靠性高,可进行动态、流水化、实时在线检测,同时对包装物品没有损伤。     

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.