超声二进制编码激励血流测量的实验研究

编码激励技术在医用超声成像中已得到了广泛的应用，但对编码激励的彩色血流成像还缺乏深入系统的研究。在以往理论研究的基础上，通过超声二进制编码激励血流测量实验，进一步研究编码激励彩色血流成像系统的可行性和成像效果。利用搭建的模拟血流循环装置和射频血流数据采集平台，首先通过单反射面回波实验研究了直接对射频回波解码和对解调后I、Q信号分别解码两种解码方法之间的关系；然后分别利用多普勒体模和乳胶管进行实验，研究了编码激励在改善穿透深度和纵向分辨率方面的优势。实验结果表明，在本实验所采用的硬件条件下，达到相同的纵向分辨率时，采用5位Barker码激励获得的穿透深度比传统方法至少增加了10mm；达到相同的穿透深度时，采用5位Barker码激励所能分辨的最小距离约相当于传统方法的1／4。     

超声编码激励功率M型多普勒栓子检测的实验研究

超声栓子检测对于研究和预防缺血性脑卒中具有重要的意义.功率M型多普勒(power M-mode Doppler,PMD)在全面直观地反映栓子运动方面具有很大的优势,但如果采用传统的长脉冲激励方法,则在检测灵敏度与距离分辨率方面就存在一定的缺陷.本文从超声栓子检测原理出发,采用编码激励方法改善PMD栓子检测效果,并在设计搭建的实验平台上研究了编码激励PMD栓子检测的性能.实验结果验证了理论分析的结论,得出编码激励有利于提高PMD栓子检测的轴向分辨率和提高栓子与背景血流信号的能量比.     

零相关窗互补码序列激励在超声血流速度剖面测量中的应用研究

为了提高超声回波信号的信噪比和空间分辨率,获取血流速度剖面,使用编码激励技术来改进传统的医学超声血流测量系统。提出一种具有"零相关窗"的互补码序列,该序列具有局部最佳非周期自相关性,可以在特定区域内完全消除旁瓣,并且采用易于硬件实现的二相编码序列。介绍了该序列的构造方法和特性,并分析了用其测量血流速度剖面的原理和方法。采用自主开发研制的激励超声测量硬件平台,通过单反射面回波实验,证实了该序列比单脉冲和13位Barker码序列具有更优良的信噪比增益。通过搭建模拟人体血流测量实验装置进行仿血流的速度剖面测量试验。实验结果表明,该序列激励超声信号同时具有优良的空间分辨率,在发射换能器的中心频率为5 MHz时,可达到0.3 mm的纵向分辨率,取得了良好的测量效果。     

功率M模式经颅多普勒超声测量系统的设计

经颅多普勒（TCD）是研究颅内大血管中血流动力学的常用技术,但传统TCD中依然存在着对大脑血管定位困难和对微栓子检测不确定等缺点。为了克服这些弊端,本研究设计了一种功率M模式TCD测量系统。该系统通过FPGA设计、USB固件驱动以及PC数据后处理等模块共同实现。数字电路模块以FPGA为核心进行状态机设计,并采用高速AD采样和双FIFO乒乓工作模式来确保良好的实时性;硬件电路部分和PC之间的数据传输依靠高速USB实现;软件模块结合功率M模式多普勒成像技术、短时傅里叶变换和伪彩色图像处理,对超声波束发射方向上整体深度的血流状态进行监测,方便定位血管深度,并为临床医生提供选通深度的声谱图信息。     

医学超声成像中的编码激励技术及其应用

与传统的脉冲回波成像技术相比 ,编码激励技术能够提高超声图像的信噪比或相应提高声束的穿透深度。本文首先介绍了编码激励成像系统的原理 ,并对医学超声诊断系统中的发射声强进行了分析 ,得出了采用编码激励技术提高超声图像信噪比的上限。然后阐述了发射编码的选取原则 ,详细介绍了白噪编码、伪随机码、Golay码、Chirp和伪 Chirp码等编码技术。最后 ,介绍了编码激励技术在 B模式成像、Doppler血流测量、B- flow成像和谐波成像中的应用。     

彩色超声成像中回归型滤波器的设计与实现

壁滤波是彩色超声血流成像系统中的一项关键技术。我们介绍了超声多普勒血流信号的产生原理及壁信号的抑制方法;其次比较了几种壁滤波器的优缺点,并且得到了回归型滤波器在低速血流信号中的有效应用;然后利用回归型滤波器对血流信号进行处理。结果表明,这是一种简单有效的壁滤波器设计实现方法,性能优于传统的壁滤波器。     

血液流速对编码激励超声血流测量系统的影响

在超声血流测量系统中应用编码激励技术可以缓解系统穿透深度和轴向分辨率的矛盾,并且提高栓子检测的灵敏度.为了更合理高效地应用编码激励技术,研究了血液流速对编码激励系统的影响.通过对不同解码滤波器和编码序列的研究发现,使用短基础序列的系统受血液流速影响较小.尖峰滤波器在流速不是很高时拥有更好地性能,而在流速较高时,使用匹配滤波器能得到稍好的结果.仿真实验表明,编码激励经颅多普勒系统中栓子能量较高且速度较快时可能会出现伪影,但可通过实时调整滤波器参数的方法解决.只要选择适当的编码方案,并在必要的时候调整脉冲压缩滤波器,血液流速对编码激励系统不会造成太大的影响.     

Barker编码激励在眼科高频超声成像中的应用研究

为了平衡医学高频超声成像中纵向分辨率和探测深度这两项指标之间的矛盾,本研究提出了在眼科超声成像中,采用13位Barker数字编码激励并结合失配滤波解码压缩方法替代传统的单脉冲激励的方法。在对比各种编解码方式的优缺点的基础上,构建了眼科超声成像平台。仿真和实验结果表明,失配滤波解码技术的输出信号主副比是匹配滤波的9.7倍。与传统的单脉冲成像在安全性、分辨率、探测深度等方面比较,编码激励技术能有效地改善眼部组织超声成像的效果,具有较强的实际应用价值和市场前景。     

超声多普勒管壁搏动和血流信号的分离研究

本研究提出利用经验模式分解(EMD)算法分解混叠有管壁成分的超声多普勒血流信号来实现管壁搏动和血流信号的分离。该方法首先将混叠有管壁搏动的超声多普勒血流信号分解为少量有限的分量,即内模函数(IMFs),然后根据管壁搏动信号与血流信号的功率比变化曲线,用比值法自动确定并去除低频管壁博动成分。在仿真实验中用提出的方法处理模拟的多普勒信号,对于靠近管腔内壁的血流信号其在频域功率谱上的相对误差为50%,在时域幅度的相对误差为45%,与高通滤波器方法的相对误差95%相比,准确性得到提高。基于个人计算机用C语言编程实现提出的算法,对实际采集的人体颈动脉多普勒信号可实现实时分离处理。结果表明:基于经验模式分解的滤波方法能有效客观地滤除管壁搏动信号,更准确地保留低频血流信号成分。     

基于Golay互补序列的20 MHz眼科超声成像方法

目的研究一种新型20 MHz眼科超声扫描成像方法,可在满足临床成像分辨力和声能安全性要求的前提下,显著提高图像的探测深度,拓展20 MHz超声频段的临床应用范围。方法通过8位Golay互补序列,激励超声换能器产生超声波。回波信息经高速采集与匹配滤波后,采用相邻正、反编码扫描线数据复用的方法交替相加,完成解码运算。在保证图像扫描线数和扫描帧频的前提下,实现实时显像。最后通过钨丝靶线和仿组织超声体模实验,验证了新的成像方法在保持原有分辨能力与扫描帧频不变的前提下,提高了图像的探测深度。结果与传统单脉冲模式相比,Golay互补编码模式成像中轴向分辨率与侧向分辨率分别达到80μm和150μm,小信号探测深度增加约0.5 cm,图像信噪比也得到显著改善。结论基于Golay互补序列实现20 MHz眼部组织超声成像,相对于传统成像方式可极大改善图像质量,具有很好的临床应用前景。     

Ultrasonic colour flow imaging

Real-time ultrasonic colour flow imaging, which was first demonstrated to be feasible only about a decade ago, has come into widespread clinical use. Ultrasound is scattered by ensembles of red blood cells. The ultrasonic frequency that gives the best signal-to-noise ratio for backscattering from blood depends on the required penetration. The frequency of ultrasound backscattered from flowing blood is shifted by the Doppler effect. The direction of flow can be determined by phase quadrature detection, and range selectivity can be provided by pulse-echo time-delay measurements. The Doppler frequency spectrum can be determined by Fourier analysis. Early two- and three-dimensional flow-imaging systems used slow manual scanning; velocity colour coding was introduced. Real-time colour flow imaging first became feasible when autocorrelation detection was used to extract the Doppler signal. Time-domain processing, which is a broad-band technique, was also soon shown to be practicable, for analysing both radio-frequency pulse-echo wavetrains and two-dimensional image speckle. Frequency- and time-domain processing both require effective cancellation of stationary echoes. The time-domain approach seems to have advantages in relation to both aliasing and the effects of attenuation in overlying tissues. Colour-coding schemes that can be interpreted without the need to refer to keys have been adopted, for both velocity and flow disturbance. Colour coding according to signal power has also been reintroduced. Three-dimensional display has been demonstrated. In interpreting colour flow images, it is important to understand the functions of critical system controls and the origins of artifacts. Various strategies can be adopted to increase the image frame rate. The problems of performance measurement and safety need to be kept under review. There are numerous opportunities for further development of ultrasonic colour flow imaging, including improvements in system design, methods of image display, the use of contrast agents and the solution of previously unexplored clinical problems.     

Detection of bubbles in blood vessels and the evaluation of their flow

The Doppler ultrasonic detection of circulating bubbles, in blood vessels, allows the study of decompression phenomena in animals and men. A method of signal processing is developed to separate the bubble Doppler signal and to estimate the corresponding gas flow. An example is given from the study of an animal decompression.     

Regional blood flow measurement with pulsed Doppler flowmeter in conscious rat

Development of techniques for the continuous measurement of regional blood flow and vascular resistance in intact small animals has been impeded primarily by the bulkiness of flow probes. The availability of an ultrasonic pulsed Doppler flowmeter system enabled us to construct miniaturized probes using 1-mm-diameter piezoelectric crystals that emit a 20-mHz signal and receive the reflected sound waves from passing blood cells. The finished flow probe is approximately 2.5-4 mm long and 2 mm in cross-sectional diameter with lumen diameters appropriate for the rat, ranging from 0.7 to 1.2 mm. This report describes the materials and methods involved in constructing and implanting the probes in rats to monitor renal, mesenteric, and hindquarter blood flow velocity. The accuracy of the pulsed Doppler method in detecting changes in regional blood flow and vascular resistance was established by the demonstration of a highly significant correlation between velocity recorded from the Doppler unit and volume flow recorded simultaneously. These data indicate that the ultrasonic pulsed Doppler flowmeter provides the opportunity to measure changes in regional blood flow and vascular resistance in a conscious freely moving rat.     

Design of a continuous-wave Doppler ultrasonic flowmeter for perivascular application

The paper details the design of the signal processing system of an ultrasonic Doppler flowmeter intended for perivascular application. The system is designed to work in conjunction with a transducer system described in an earlier paper, in a range of vessels varying from 5 mm to 12 mm. The system incorporates conventional quadrature processing for directional discrimination and uses phaselocked loop technology to extract signals corresponding to the instantaneous mean frequency (velocity equivalent). The use of a PLL also permits the extraction of a quasi-spectral analysis signal. The baseline stability of the Doppler system is enhanced by the use of an auto-zeroing system which enables the system to resolve Doppler shifts down to 20Hz. Testing of the complete transducer/signal processor system in a hydraulic rig demonstrates the ability of the flowmeter to accurately measure both steady and pulsatile flow.     

Photoacoustic and high-frequency power Doppler ultrasound biomicroscopy: a comparative study

Both photoacoustic imaging and power Doppler ultrasound are capable of producing images of the vasculature of living subjects, however, the contrast mechanisms of the two modalities are very different. We present a quantitative and objective comparison of the two methods using phantom data, highlighting relative merits and shortcomings. An imaging system for combined photoacoustic and high-frequency power Doppler ultrasound microscopy is presented. This system uses a swept-scan 25-MHz ultrasound transducer with confocal dark-field laser illumination optics. A pulse-sequencer enables ultrasonic and laser pulses to be interlaced so that photoacoustic and power Doppler ultrasound images can be coregistered. Experiments are performed on flow phantoms with various combinations of vessel size, flow velocity, and optical wavelength. For the task of blood volume detection, power Doppler is seen to be advantageous for large vessels and high flow speeds. For small vessels with low flow speeds, photoacoustic imaging is seen to be more effective than power Doppler at the detection of blood as quantified by receiver operating characteristic analysis. A combination of the two modes could provide improved estimates of fractional blood volume in comparison with either mode used alone.     

一种便携式多普勒胎心检测系统的设计及实现

本研究设计并实现了一款便携式,全数字,用于围产期胎儿心率检测的多普勒胎心系统,其采用对超声回波加窗,数字相乘等方法获取频移信号,并可对特定组织深度进行运动检测。该系统由CPLD超声激励及采集电路、MCU及外围电路和系统软件三部分组成。与两款商用胎心仪相比,本系统准确度较高,能够稳定可靠的对胎心进行检测。     

用超声方法检测血栓的物理实验研究

本文使用基于ＴＭＳ３２０Ｃ２５高速信号处理卡的双通道脉冲破经颅多普勒血流分析仪,建立起模拟血栓实验平台,从频域和时域两方面采集模拟血栓数据,并对血栓的特性及其检测方法进行研究,实验结果表明,从时域延迟和频谱特征变化两方面来检测血栓是一种应用前景的方法。