本文選題：激光散斑襯比度成像 + 光散粒噪聲　； 參考：《南京理工大學(xué)》2017年碩士論文

【摘要】：激光散斑襯比度成像方法作為一種可用于血流監(jiān)測的光學(xué)成像方法,具有非接觸、時空分辨率高、簡易性等優(yōu)點(diǎn),已經(jīng)在視網(wǎng)膜和腦皮層血流監(jiān)測領(lǐng)域有所應(yīng)用。然而成像系統(tǒng)中的噪聲影響以及生物組織中多次散射對散斑動態(tài)變化影響的研究尚不深入,還有諸多問題需要解決。本文從理論分析、數(shù)值模擬和實(shí)驗(yàn)測量三方面對激光散斑襯比度成像中的CCD噪聲影響展開了討論。鑒于激光散斑成像系統(tǒng)中的光散粒噪聲作為CCD固有噪聲難以消除,亦是成像系統(tǒng)的主要噪聲來源,文中首先對光散粒噪聲對襯比度測量的影響進(jìn)行了理論分析,認(rèn)為由于光散粒噪聲的存在使得襯比度測量結(jié)果偏差值會隨著光強(qiáng)的減小而增大。之后,運(yùn)用基于變量相關(guān)的動態(tài)散斑模擬方法得到了散斑圖像,并對模擬散斑圖像進(jìn)行襯比分析,從而驗(yàn)證了理論分析的正確性。進(jìn)而實(shí)驗(yàn)結(jié)果表明:光散粒噪聲在弱光條件下對襯比度測量準(zhǔn)確性的影響較大;且通過實(shí)驗(yàn)測量獲得了表征CCD散粒噪聲的參數(shù)——轉(zhuǎn)換增益γ。結(jié)合光散粒噪聲和暗噪聲給出了散斑襯比度CCD噪聲影響的修正公式�？紤]到CCD噪聲修正方法可應(yīng)用于多次散射的散斑襯比度成像研究領(lǐng)域,因而從理論公式推導(dǎo)和實(shí)驗(yàn)研究兩方面對其進(jìn)行研究。首先根據(jù)擴(kuò)散相關(guān)譜理論,推導(dǎo)了基于多次散射理論的擴(kuò)散散斑襯比度的理論計算公式,給出了擴(kuò)散散斑襯比度與曝光時間、光源-探測器距離和布朗運(yùn)動擴(kuò)散系數(shù)關(guān)系的解析解。之后,構(gòu)建了擴(kuò)散散斑襯比度成像的實(shí)驗(yàn)裝置,并對實(shí)驗(yàn)結(jié)果修正了散粒噪聲影響,進(jìn)而分別根據(jù)兩種關(guān)系:曝光時間一定時,襯比度隨光源-探測器距離變化的關(guān)系;光源-探測器距離一定時,襯比度隨曝光時間變化的關(guān)系,通過擬合求解得到擴(kuò)散系數(shù)值,并與理論值進(jìn)行比較,從而驗(yàn)證了利用擴(kuò)散散斑襯比度成像方法進(jìn)行定量測量的有效性。本文的研究結(jié)果可為提高激光散斑襯比度成像方法的測量準(zhǔn)確性提供參考。
[Abstract]:As an optical imaging method for blood flow monitoring, laser speckle contrast imaging has many advantages, such as non-contact, high spatial and temporal resolution, simplicity and so on. It has been applied in the field of retinal and cerebral cortex blood flow monitoring. However, the effects of noise and multiple scattering in biological tissues on the dynamic change of speckle are not well studied, and there are still many problems to be solved. In this paper, the influence of CCD noise in laser speckle contrast imaging is discussed from three aspects: theoretical analysis, numerical simulation and experimental measurement. As the inherent noise of CCD is difficult to eliminate in the laser speckle imaging system, it is also the main noise source of the imaging system. In this paper, the influence of the laser speckle noise on the contrast measurement is analyzed theoretically. It is considered that the deviation value of contrast measurement results will increase with the decrease of light intensity due to the existence of particle noise. After that, the dynamic speckle simulation method based on variable correlation is used to obtain the speckle image, and the contrast ratio of the simulated speckle image is analyzed, which verifies the correctness of the theoretical analysis. The experimental results show that the accuracy of contrast measurement is greatly affected by the light shot noise under the condition of low light, and the parameter-conversion gain 緯 which characterizes the CCD shot noise is obtained by experimental measurement. The correction formula of speckle contrast ratio CCD noise is given by combining the light speckle noise and dark noise. Considering that the CCD noise correction method can be used in the field of speckle contrast imaging with multiple scattering, the theoretical formula and the experimental study are studied. Based on the diffusion correlation spectrum theory, the theoretical formula of diffusive speckle contrast ratio based on multiple scattering theory is derived, and the diffusive speckle contrast ratio and exposure time are given. The analytical solution of the relation between the distance between the light source and the detector and the diffusion coefficient of the Brownian motion. Then, an experimental device for diffusive speckle contrast imaging is constructed, and the effect of shot noise on the experimental results is corrected, which is based on two relationships: the relation of contrast ratio with the distance between light source and detector when the exposure time is constant; When the distance between the light source and the detector is constant, the contrast ratio varies with the exposure time, and the diffusion coefficient is obtained by fitting, and compared with the theoretical value. The effectiveness of quantitative measurement using diffusion-speckle contrast imaging method is verified. The results of this paper can be used to improve the accuracy of laser speckle contrast imaging.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN249

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本文編號：1911962