基于微纳米颗粒的光声多普勒微循环流速测量

发布时间：2018-08-07 15:09

【摘要】：人体的微循环系统主要在微血管，微血管也叫毛细血管，是血液与周围组织进行物质交换的场所，而流速是表征血管性能的一个重要参数，微血管或周围组织的病变会导致血流发生变化。微血管的流速测量和成像对于心脑血管等疾病的预防及治疗有着非常重要的作用。目前的血液流速测量主要是利用多普勒技术，主要包括超声多普勒和激光多普勒流速测量。超声多普勒测速的原理是利用流体中运动微粒散射声波的多普勒频移来获得液体流速信息，由于人体内组织的缓慢运动，在测量低流速时，获得的多普勒信号不只来自于流动的微粒还有管壁的影响，因此在低流速下超声多普勒的测量受到很大制约；激光多普勒的原理与超声多普勒相似，也是利用了运动微粒的光散射，虽然它能够测得较低的流速，但是测量深度有限，并且不能获得流速的方向信息。光声多普勒技术很好的解决了这一问题，它兼有声学测量和光学测量的优点，有很高的光学对比度和较低的背景噪声。本课题根据光声多普勒频移与流速的线性关系，设计了一套以锁相放大器为核心的低流速测量系统，通过光声多普勒信号与参考信号混频运算得到光声多普勒频移信号，然后对其进行快速傅里叶变换得到多普勒频移，进而计算出平均流速；为了验证流速与超声探头的夹角（多普勒角度）对多普勒频移的影响，以丰富和补充光声多普勒理论，对原有的实验系统做了改进，，利用步进电机带动超声探头的旋转，完成了对多普勒角度的扫描。实验结果表明，多普勒角度的余弦值与多普勒频移呈线性关系，本文提出的方法适用于低流速的测量，相比于其它多普勒流速测量技术，不但有较好的测量准确性，还能判断流速方向，并讨论了多普勒角度与多普勒频移的关系，作为一种新技术它可能为微血管低流速测量提出了一种新的无创测量手段。
[Abstract]:The microcirculation system of the human body is mainly in the microvessels, which are also called capillaries. They are the places where the blood exchanges substances with the surrounding tissues, and the velocity of flow is an important parameter to characterize the performance of blood vessels. Changes in blood flow can result from changes in microvessels or surrounding tissues. Microvascular velocity measurement and imaging play an important role in the prevention and treatment of cardiovascular and cerebrovascular diseases. At present, Doppler technique is mainly used to measure blood velocity, including ultrasonic Doppler and laser Doppler velocity measurement. The principle of ultrasonic Doppler velocimetry is to obtain the velocity information of liquid by Doppler frequency shift of moving particles scattering sound wave in fluid. Because of the slow movement of human body tissue, when measuring low velocity of velocity, The Doppler signal is obtained not only from the flowing particles but also from the tube wall, so the measurement of ultrasonic Doppler at low velocity is greatly restricted; the principle of laser Doppler is similar to that of ultrasonic Doppler. The light scattering of moving particles is also used. Although it can measure low velocity, the depth of measurement is limited, and the direction information of velocity can not be obtained. Photoacoustic Doppler technique solves this problem very well. It has the advantages of both acoustic measurement and optical measurement. It has high optical contrast and low background noise. According to the linear relationship between photoacoustic Doppler frequency shift and velocity, a low velocity measurement system with phase-locked amplifier as the core is designed in this paper. The photoacoustic Doppler frequency shift signal is obtained by mixing the photoacoustic Doppler signal with the reference signal. Then the Doppler frequency shift is obtained by fast Fourier transform, and the average velocity is calculated. In order to verify the influence of the angle between the velocity and the ultrasonic probe (Doppler angle) on the Doppler frequency shift, the photoacoustic Doppler theory is enriched and supplemented. The original experimental system was improved and the ultrasonic probe was rotated by stepper motor, and the Doppler angle was scanned. The experimental results show that there is a linear relationship between the Doppler angle cosine value and the Doppler frequency shift. The proposed method is suitable for low velocity measurement. Compared with other Doppler velocity measurement techniques, the proposed method not only has a good accuracy. The relationship between Doppler angle and Doppler frequency shift is also discussed. As a new technique, it may provide a new non-invasive method for microvascular low velocity measurement.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.6

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