【摘要】：生物組織光聲成像是一種新型的醫(yī)學(xué)成像技術(shù),它同時具有光學(xué)成像的強(qiáng)對比度和超聲深層組織成像分辨率高的優(yōu)勢,能夠?qū)ι锝M織提供結(jié)構(gòu)的、功能的和分子的成像。在光聲成像中,激光照射生物組織,由于光聲效應(yīng)產(chǎn)生光聲信號。信號通過一個寬帶的換能器接收,小信號放大器放大,數(shù)據(jù)采集卡采樣等步驟,得到了儲存在計算機(jī)上的光聲信號。目前,對生物組織光聲信號的研究主要集中在時域分析�？墒�,時域信號受到各種外界因素的影響,比如激光光源的激發(fā)脈沖、換能器的頻率響應(yīng)、測量系統(tǒng)的傳遞函數(shù)等。這些因素導(dǎo)致時域分析得到的圖像只能夠定性地反映光吸收體的相對強(qiáng)弱。這樣就存在一個問題,即對同樣的一個樣品,不同的儀器甚至相同的儀器不同的操作者得到的結(jié)果無法做到定量的比較。本文以定量化為目標(biāo),在頻域上對光聲信號作了深入的研究,并取得了以下研究成果：本文首先從理論上研究了隨機(jī)分布的單一尺寸光吸收體的光聲信號頻譜特征。理論分析表明功率譜斜率受到激光照射函數(shù)、光吸收體的相關(guān)函數(shù)、指向性函數(shù)、換能器響應(yīng)和估計參數(shù)的帶寬等因素影響,并且對這些因素的影響作了定量的分析。然后,通過一個理想的實(shí)驗(yàn)證明了上述理論方程。實(shí)驗(yàn)表明：當(dāng)通過校準(zhǔn)的方式移除外界的影響因素之后,能夠得到只和組織的微結(jié)構(gòu)有關(guān)的頻譜信息。最后,我們從校準(zhǔn)信號中取出斜率參數(shù),發(fā)現(xiàn)不同的系統(tǒng)得到的校準(zhǔn)之后的斜率參數(shù)可以進(jìn)行定量的比較。即我們從理論上和實(shí)驗(yàn)上證明了校準(zhǔn)的光聲頻譜信號具有和操作者以及設(shè)備無關(guān)的特征。這個工作對以后做定量化測量及比較是非常有意義的。本文根據(jù)對光聲信號頻域理論分析,提出了用頻譜擬合的方式去測量深埋在渾濁媒質(zhì)中隨機(jī)分布的光吸收體尺寸的方法。頻譜理論指出,功率譜信號的低頻段和光吸收體尺寸具有一一對應(yīng)的關(guān)系。因此,可以從低頻段提取參數(shù)信息,去定量地測量粒子尺寸。理想的樣品實(shí)驗(yàn)證明了上述方法的有效性。我們準(zhǔn)確地測量出三種微顆粒的尺寸信息。由于頻譜方法可以使用低頻段的光聲信號來測量樣品,所以該方法適用于較深處組織的定量測量。此外,本文以血細(xì)胞聚集這一現(xiàn)象為模型,對混合尺寸的隨機(jī)分布微顆粒的光聲信號進(jìn)行了理論分析,給出一般性的頻譜表達(dá)式。由于血細(xì)胞的聚集情況比較復(fù)雜,我們引入等效粒子尺寸的概念,定量的描述了混合粒子的整體特征。最后,實(shí)驗(yàn)得到的混合粒子的特征尺寸和理論吻合很好。因此,用混合粒子的頻譜進(jìn)行定量測量擴(kuò)展了單一尺寸的應(yīng)用模型,具有更實(shí)際的應(yīng)用價值。
[Abstract]:Biological tissue photoacoustic imaging is a new type of medical imaging technology. It has the advantages of strong contrast of optical imaging and high resolution of ultrasonic deep tissue imaging, which can provide structural, functional and molecular imaging for biological tissue. In photoacoustic imaging, photoacoustic signals are produced by laser irradiation on biological tissues. The signal is received by a wideband transducer, amplified by a small signal amplifier and sampled by a data acquisition card. The photoacoustic signal stored on the computer is obtained. At present, the research of biological tissue photoacoustic signal is mainly focused on time domain analysis. However, the time domain signal is affected by various external factors, such as the excitation pulse of the laser source, the frequency response of the transducer, the transfer function of the measurement system, and so on. These factors can only reflect the relative strength of optical absorber qualitatively. The problem is that for the same sample, different instruments and even the same instrument, the results obtained by different operators can not be compared quantitatively. Aiming at quantification, the photoacoustic signal in frequency domain is studied deeply in this paper, and the following research results are obtained: firstly, the spectrum characteristics of photoacoustic signal with random distribution of single size photoabsorber are studied theoretically in this paper. Theoretical analysis shows that the slope of power spectrum is affected by the factors such as laser irradiation function, correlation function of optical absorber, directivity function, transducer response and the bandwidth of estimating parameters, and the influence of these factors is analyzed quantitatively. Then, the above theoretical equations are proved by an ideal experiment. The experimental results show that the spectrum information related only to the microstructure of the tissue can be obtained when the external factors are removed by means of calibration. Finally, we take the slope parameters from the calibration signal and find that the slope parameters after calibration can be quantitatively compared with each other. That is, we prove theoretically and experimentally that the calibrated photoacoustic spectrum signal has characteristics independent of operator and equipment. This work is very meaningful for quantitative measurement and comparison in the future. Based on the theoretical analysis of the frequency domain of photoacoustic signals, this paper presents a method of measuring the size of light absorbers with random distribution deeply buried in turbid media by means of spectrum fitting. The spectrum theory indicates that the low frequency band of the power spectrum signal has a one-to-one correspondence with the size of the optical absorber. Therefore, the parameter information can be extracted from the low frequency band to measure the particle size quantitatively. The experimental results show that the proposed method is effective. We accurately measured the size information of three kinds of microparticles. Because the spectrum method can be used to measure samples with low frequency band photoacoustic signals, this method is suitable for quantitative measurement of deeper tissues. In addition, taking the phenomenon of blood cell aggregation as a model, the photoacoustic signals of randomly distributed microparticles of mixed size are theoretically analyzed, and a general spectrum expression is given. Because the aggregation of blood cells is complicated, we introduce the concept of equivalent particle size and describe the global characteristics of mixed particles quantitatively. Finally, the characteristic size of the mixed particles is in good agreement with the theory. Therefore, the application model of single size is extended by using the spectrum of mixed particles, which has more practical application value.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：Q6-33;TN911.6

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本文編號：2377575