本文選題：高強度聚焦超聲 + 非線性聲場��； 參考：《南京大學》2014年博士論文

【摘要】：高強度聚焦超聲(High Intensity Focused Ultrasound, HIFU)是一種治療實體良／惡性腫瘤的非侵入性新興治療技術(shù),焦點的聲強可高達103W/cm2,能夠在短時間內(nèi)(秒級)使焦域組織凝固性壞死。為了更好的控制HIFU治療過程中的臨床效果,需要對HIFU的非線性聲場進行準確描述。本文首先介紹了HIFU非線性聲場的測量方法和相關(guān)理論模型,在此基礎(chǔ)上討論了沖擊波產(chǎn)生后,HIFU聲場的定征方法。 針對大張角強聚焦換能器,本論文提出了頻域-時域結(jié)合算法計算其非線性聲場分布的方法。利用橢球坐標系非線性方法(SBE)描述聲場分布,在頻域計算聲場衍射和衰減效應,在時域計算非線性效應。該方法計算結(jié)果與Rayleigh積分及傳統(tǒng)頻域算法計算結(jié)果吻合的很好,證明了該計算方法的可靠性。沖擊波產(chǎn)生后,傳統(tǒng)頻域算法計算時會產(chǎn)生明顯的波形振蕩,利用該方法不僅可以有效的避免沖擊波波形振蕩而且還縮短了計算時間。 沖擊波產(chǎn)生后,由于其極限條件(強聲壓,寬頻譜,高空間分辨率),直接測量其聲場分布不僅耗時且對測量設(shè)備的要求較高。本論文提出實驗測量與理論計算相結(jié)合的方式定征大張角強聚焦換能器的非線性聲場。首先,忽略換能器封裝等因素,將其視作表面均一振動的振子,在線性聲場條件下確定其有效參數(shù)；其次,利用焦點波形二次諧波與基波之比,結(jié)合實驗測量結(jié)果和模型計算結(jié)果得到驅(qū)動電壓與聲源表面聲壓幅值的關(guān)系；最后,利用SBE模型計算在任意驅(qū)動下的非線性聲場分布。將本方法得到的焦點波形與光纖水聽器測量結(jié)果做對比,結(jié)果表明：在較低驅(qū)動下,由于非線性效應不足以產(chǎn)生足夠高的二次諧波,本方法不能用于描述低驅(qū)動下的聲場分布；當沖擊波產(chǎn)生后,測量波形與仿真結(jié)果在峰峰值以及相位上存在差距,兩者的頻譜在50MHz范圍內(nèi)吻合的很好,這說明沖擊波產(chǎn)生后,光纖水聽器的測量波形可能受限于帶寬等原因,與實際結(jié)果存在一定的差距。本章中提出的方法有助于準確定征沖擊波產(chǎn)生后的HIFU聲場。 本論文利用實驗測量與理論計算相結(jié)合的方法定征HIFU非線性聲場,該工作將進一步推進對HIFU聲場非線性分布的研究,更加準確的預測超聲在活體組織中的傳播,從而促進高強度聚焦超聲在臨床的應用。
[Abstract]:High intensity focused ultrasound (HIFU) high Intensity Focused Ultrasound, HIFU) is a new non-invasive treatment technique for solid benign and malignant tumors. The focal sound intensity can be up to 103 W / cm ~ 2 and can cause coagulation necrosis of focal area tissue in a short time (second order). In order to better control the clinical effect of HIFU, it is necessary to accurately describe the nonlinear sound field of HIFU. In this paper, the measurement method and related theoretical model of HIFU nonlinear sound field are introduced, and the method of determining the acoustic field after shock wave is discussed. In this paper, a method for calculating the nonlinear acoustic field distribution of a large angle strong focusing transducer is proposed by combining frequency-domain and time-domain algorithm. The nonlinear method of ellipsoidal coordinate system (SBE) is used to describe the distribution of sound field. The diffraction and attenuation effects of sound field in frequency domain and nonlinear effect in time domain are calculated. The calculated results of this method are in good agreement with the Rayleigh integral and the traditional frequency domain algorithm, which proves the reliability of the method. After the shock wave is produced, the traditional frequency-domain algorithm will produce obvious waveform oscillation, which can not only effectively avoid the shock wave oscillation but also shorten the calculation time. After the shock wave is produced, due to its limit conditions (strong sound pressure, wide frequency spectrum, high spatial resolution), it is not only time consuming to measure the sound field distribution directly, but also the requirement of measuring equipment is high. In this paper, the nonlinear sound field of the strong focus transducer with large angle of tension is determined by combining the experimental measurement with the theoretical calculation. First of all, the transducer packaging is ignored, and it is regarded as a vibrator with homogeneous surface vibration, and its effective parameters are determined under the condition of linear sound field. Secondly, the ratio of the second harmonic to the fundamental wave of the focus waveform is used. The relationship between the driving voltage and the amplitude of sound pressure on the sound source surface is obtained by combining the experimental results with the results of the model calculation. Finally, the nonlinear sound field distribution under arbitrary driving is calculated by using the SBE model. The focus waveform obtained by this method is compared with the measurement results of fiber-optic hydrophone. The results show that the method can not be used to describe the sound field distribution under low driving because the nonlinear effect is not enough to produce high second harmonic. When the shock wave is produced, there is a gap between the measured waveform and the simulation result in peak, peak and phase. The spectrum of the two waves is in good agreement in the range of 50MHz, which indicates that after the shock wave is produced, The measurement waveform of fiber-optic hydrophone may be limited by bandwidth, which is far from the actual results. The method proposed in this chapter is helpful to determine the HIFU sound field after the shock wave is produced. In this paper, the nonlinear acoustic field of HIFU is characterized by the combination of experimental measurement and theoretical calculation. This work will further promote the study of the nonlinear distribution of HIFU sound field, and more accurately predict the propagation of ultrasound in living tissue. So as to promote the clinical application of high intensity focused ultrasound.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：R445.1

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相關(guān)期刊論文 前1條

1 李全義;李發(fā)琪;壽文德;;高強度聚焦超聲(HIFU)的聲場檢測[J];世界科技研究與發(fā)展;2007年06期

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本文編號：1913534