【摘要】：超聲成像作為現(xiàn)代醫(yī)學(xué)四大影像技術(shù)之一,以其強(qiáng)度低、對人體無創(chuàng)傷、價格低廉、方便、顯示方法多樣等優(yōu)點被廣泛的應(yīng)用。在醫(yī)學(xué)超聲成像系統(tǒng)中,圖像信噪比和分辨率是評價成像質(zhì)量的兩個重要因素。由于生物組織對于超聲效應(yīng)受限程度的限制,傳統(tǒng)單脈沖激勵超聲成像的脈沖幅值不能超過一定閾值,增加激勵信號時寬,可提高超聲功率,提高深部組織回波信噪比,但會降低分辨率。編碼激勵技術(shù)能夠在保證信噪比或探測深度的同時,提高圖像的圖像分辨率。相對于傳統(tǒng)超聲脈沖回波系統(tǒng),超聲成像的編碼激勵系統(tǒng)設(shè)計和實現(xiàn)有其獨特的特點,還有很多值得研究的地方。其中提高脈沖壓縮信噪比和分辨率,仍然是超聲成像編碼激勵技術(shù)研究的熱點之一。 基于編碼激勵和脈沖壓縮技術(shù),本文理論上推導(dǎo)和分析線性調(diào)頻激勵信號的帶寬、時寬、幅度包絡(luò)因素對脈沖壓縮分辨率的影響,并通過仿真和實驗驗證理論推導(dǎo)的正確性。針對超聲換能器頻率響應(yīng)特征,分別用不同帶寬、時寬和幅度包絡(luò)的線性調(diào)頻信號激勵超聲換能器,通過對比激勵換能器前后能量和主瓣寬度的變化,探討線性調(diào)頻信號帶寬、時寬和幅度包絡(luò)對激勵超聲換能器獲得波形脈沖壓縮信噪比和分辨率的影響。從而研究超聲線性調(diào)頻信號的最佳激勵方式。 本文研究的主要內(nèi)容： (1)理論推導(dǎo)線性調(diào)頻信號匹配濾波脈沖壓縮,通過對推導(dǎo)所得表達(dá)式分析線性調(diào)頻信號帶寬、時寬和幅度包絡(luò)參數(shù)對脈沖壓縮分辨率的影響。 (2)設(shè)計匹配濾波器,選用五組不同的帶寬,五組不同時寬和六組不同系數(shù)二次曲線幅度調(diào)制的線性調(diào)頻信號激勵匹配濾波進(jìn)行脈沖壓縮,仿真對比脈沖壓縮所得波形的分辨率。計算機(jī)控制任意波形發(fā)生器發(fā)出實驗所用的幾組線性調(diào)頻信號,激勵超聲換能器,對接收到的超聲回波信號分別通過匹配濾波,實驗研究脈沖壓縮所得波形分辨率。 (3)針對超聲換能器具有的等效頻帶特性,選用五組不同的帶寬,五組不同時寬和六組不同系數(shù)二次曲線幅度調(diào)制的線性調(diào)頻信號激勵超聲換能器,再進(jìn)行脈沖壓縮。對比激勵換能器前后能量和主瓣寬度的變化,探討線性調(diào)頻信號的最佳激勵方式。 本文研究表明： (1)線性調(diào)頻信號脈沖壓縮的主瓣寬度與其帶寬和時寬成反比,隨著時間的增加主瓣寬度幾乎只決定信號帶寬。 (2)線性調(diào)頻信號激勵換能器能量的損失與信號帶寬成正比,與信號時寬無關(guān)。說明線性調(diào)頻信號的帶寬越大激勵換能器后信噪比損失越大。 (3)幅度包絡(luò)調(diào)制的線性調(diào)頻信號匹配濾波脈沖壓縮所得信號的分辨率與各信號頻段所占的比重有關(guān)。若其中心頻段所占的比重越小,脈沖壓縮后主瓣寬度越窄,即分辨率越好,當(dāng)調(diào)頻信號激勵超聲換能器,信號兩端頻段能量損失較大,所以中心頻段比重的大線性調(diào)頻信號激勵超聲換能器能量損失較小,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.
【學(xué)位授予單位】：陜西師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TP391.41;R445.1

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