超声线性调频信号脉冲压缩分辨率研究

发布时间：2018-08-07 12:48

【摘要】：超声成像作为现代医学四大影像技术之一,以其强度低、对人体无创伤、价格低廉、方便、显示方法多样等优点被广泛的应用。在医学超声成像系统中,图像信噪比和分辨率是评价成像质量的两个重要因素。由于生物组织对于超声效应受限程度的限制,传统单脉冲激励超声成像的脉冲幅值不能超过一定阈值,增加激励信号时宽,可提高超声功率,提高深部组织回波信噪比,但会降低分辨率。编码激励技术能够在保证信噪比或探测深度的同时,提高图像的图像分辨率。相对于传统超声脉冲回波系统,超声成像的编码激励系统设计和实现有其独特的特点,还有很多值得研究的地方。其中提高脉冲压缩信噪比和分辨率,仍然是超声成像编码激励技术研究的热点之一。基于编码激励和脉冲压缩技术,本文理论上推导和分析线性调频激励信号的带宽、时宽、幅度包络因素对脉冲压缩分辨率的影响,并通过仿真和实验验证理论推导的正确性。针对超声换能器频率响应特征,分别用不同带宽、时宽和幅度包络的线性调频信号激励超声换能器,通过对比激励换能器前后能量和主瓣宽度的变化,探讨线性调频信号带宽、时宽和幅度包络对激励超声换能器获得波形脉冲压缩信噪比和分辨率的影响。从而研究超声线性调频信号的最佳激励方式。本文研究的主要内容： (1)理论推导线性调频信号匹配滤波脉冲压缩,通过对推导所得表达式分析线性调频信号带宽、时宽和幅度包络参数对脉冲压缩分辨率的影响。 (2)设计匹配滤波器,选用五组不同的带宽,五组不同时宽和六组不同系数二次曲线幅度调制的线性调频信号激励匹配滤波进行脉冲压缩,仿真对比脉冲压缩所得波形的分辨率。计算机控制任意波形发生器发出实验所用的几组线性调频信号,激励超声换能器,对接收到的超声回波信号分别通过匹配滤波,实验研究脉冲压缩所得波形分辨率。 (3)针对超声换能器具有的等效频带特性,选用五组不同的带宽,五组不同时宽和六组不同系数二次曲线幅度调制的线性调频信号激励超声换能器,再进行脉冲压缩。对比激励换能器前后能量和主瓣宽度的变化,探讨线性调频信号的最佳激励方式。本文研究表明： (1)线性调频信号脉冲压缩的主瓣宽度与其带宽和时宽成反比,随着时间的增加主瓣宽度几乎只决定信号带宽。 (2)线性调频信号激励换能器能量的损失与信号带宽成正比,与信号时宽无关。说明线性调频信号的带宽越大激励换能器后信噪比损失越大。 (3)幅度包络调制的线性调频信号匹配滤波脉冲压缩所得信号的分辨率与各信号频段所占的比重有关。若其中心频段所占的比重越小,脉冲压缩后主瓣宽度越窄,即分辨率越好,当调频信号激励超声换能器,信号两端频段能量损失较大,所以中心频段比重的大线性调频信号激励超声换能器能量损失较小,即信噪比越好。
[Abstract]:As one of the four major imaging techniques in modern medicine, ultrasound imaging has been widely used for its low intensity, no trauma, low price, convenience and diversity of display methods. In medical ultrasound imaging system, image signal-to-noise ratio and resolution are two important factors to evaluate imaging quality. Because biological tissue is limited to the ultrasonic effect Degree limit, the pulse amplitude of traditional monopulse excitation ultrasound imaging can not exceed a certain threshold, increase the width of the excitation signal, improve the ultrasonic power and improve the signal to noise ratio of the deep tissue echo, but reduce the resolution. The coding and excitation technology can improve the image resolution while ensuring the signal to noise ratio or the depth of detection. The traditional ultrasonic pulse echo system, the design and implementation of the ultrasonic imaging coding and excitation system have its unique characteristics, and there are many places to be studied. Among them, improving the signal to noise ratio and resolution of pulse compression is still one of the hotspots in the research of ultrasonic imaging coding excitation technology.
Based on the coded excitation and pulse compression technology, this paper theoretically derives and analyzes the influence of the bandwidth, time width and amplitude envelope on the resolution of the pulse compression, and proves the correctness of the theoretical derivation by simulation and experiment. The frequency response characteristics of the ultrasonic transducer are used to use the different bandwidth, time width and amplitude packet respectively. The linear frequency modulation signal of the collaterals is used to stimulate the ultrasonic transducer. By comparing the changes of the energy and the width of the main lobe, the influence of the bandwidth, time width and amplitude envelope on the signal to noise ratio and resolution of the waveform pulse compression is discussed. The optimal excitation mode of the ultrasonic linear frequency modulation signal is studied.
The main contents of this paper are as follows:
(1) the linear FM signal matching filter pulse compression is derived theoretically, and the influence of the bandwidth, the time width and the amplitude envelope parameters on the pulse compression resolution is analyzed by the derived expression.
(2) design the matched filter, select five groups of different bandwidth, five groups of different width and six different coefficient two curve amplitude modulation signal excitation matching filter to carry out pulse compression, simulate and compare the resolution of the waveform obtained by pulse compression. Computer control a few sets of linear frequency modulation used by arbitrary waveform generator. The signal is used to excite the ultrasonic transducer. The received ultrasonic echo signal is filtered by matched filtering. The waveform resolution obtained by pulse compression is experimentally studied.
(3) in view of the equivalent frequency band characteristics of the ultrasonic transducer, a linear frequency modulation signal excited ultrasonic transducer with five groups of different bandwidth, five groups of different width and six different coefficients of two curve amplitude modulation is used, and then the pulse compression is carried out. The best change of the energy and the width of the main lobe of the excitation transducer is compared. The optimal linear frequency modulation signal is discussed. The way to motivate.
The study shows that:
(1) The main lobe width of LFM signal pulse compression is inversely proportional to its bandwidth and time width, and the main lobe width almost determines the signal bandwidth with the increase of time.
(2) the energy loss of the linear frequency modulation signal excitation transducer is proportional to the signal bandwidth, and has nothing to do with the width of the signal. It shows that the greater the bandwidth of the LFM signal, the greater the signal to noise ratio loss after the transducer is stimulated.
(3) the resolution of the signal obtained by the matched filter pulse compression of the LFM signal of the amplitude envelope modulation is related to the proportion of each signal frequency band. If the proportion of the central frequency band is smaller, the width of the main lobe is narrower after the pulse compression, that is, the better the resolution is, the energy loss of the frequency band at both ends of the signal is greater when the frequency modulation signal is excited by the ultrasonic transducer. Therefore, the large LFM signal excited by the central frequency band has little energy loss, that is, the better signal to noise ratio.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP391.41;R445.1

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