共查询到19条相似文献,搜索用时 140 毫秒
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光声成像兼具声学成像和光学成像两者的优点, 因而成为近十年来发展最迅速的生物医学成像技术之一. 本文介绍了光声成像的特点及其相对于广泛应用的光学成像技术和声学成像技术的优点; 其次, 解释了光声成像的成像原理, 在此基础上介绍了光声断层成像和光声显微镜这两种典型的光声成像方案, 并介绍了它们的技术特点; 然后, 介绍了光声成像对生物组织的生化特性、组织力学特性、血液流速分布、温度分布参数、微结构特性等多信息参量的提取能力, 及其在生物系统的结构成像、功能成像、代谢成像、分子成像、基因成像等多领域的应用; 最后, 展望了光声成像在生物医学领域的应用潜力并讨论了其局限性. 相似文献
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非线性光学相位共轭技术可将经过散射介质后产生畸变的光学波前进行修复.本文基于光参量放大(OPA)过程的光学相位共轭(OPC)特性,进行了光学相位共轭图像修复和增强的实验研究.基于大能量532 nm皮秒抽运激光和大口径非线性光学晶体KTiOPO_4(KTP)(Ⅱ类相位匹配),对经过牛奶乳浊液后已无法识别的1064 nm近红外光学图像,进行相位共轭修复,修复后的图像分辨率达12线/mm,此外,结合OPA过程的光学增益特性,实现了超过17 dB的光学图像增强,为现有三波混频光学相位共轭修复畸变所获图像增益的最大值.在此基础上,峰值信噪比较修复之前有160%的提升.考虑到光参量过程所具有的波长可调谐特性,在实际应用中,可根据需要,选择与生物组织的光学治疗窗口相匹配的成像波长,从而保证更长的穿透深度,提升生物组织成像和医学无损检测的效果. 相似文献
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非线性声参量计算机模拟成像 总被引:2,自引:2,他引:0
非线性声参量B/A是生物组织超声辨认的一个重要的新参量.本文从Burgers’方程出发分析了有限振幅平面声波在层状介质中的非线性传播理论,并将它用于二次谐波的声成像,利用通常的CT算法而得的二次谐波数据进行了非线性声参量的计算机模拟成像,用滤波逆投影算法进行图像重建,对简单的样品模型得到了较好的非线性声参量断层图像. 相似文献
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根据Jacobson的液体分子自由程理论和液体声速与分子自由程的关系,推导出多元有机混合液声速的温度系数、压力系数和非线性声参量B/A的计算公式,并根据组成多元有机混合液各组分特性参量(密度、自由程、非线性声参量B/A、等压膨胀系数、等温压缩系数等),利用给出的公式对声速的温度系数、压力系数、非线性声参量B/A进行了数值计算,并将计算结果与实验结果进行了比较. 相似文献
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Study of acoustic nonlinearity parameter imaging methods in reflection mode for biological tissues 总被引:2,自引:0,他引:2
Gong X Zhang D Liu J Wang H Yan Y Xu X 《The Journal of the Acoustical Society of America》2004,116(3):1819-1825
Three novel methods for acoustic nonlinearity parameter B/A imaging in reflection mode are developed in this paper. They are: (1) the acoustic nonlinearity parameter B/A tomography by detecting reflective second harmonic wave, (2) the B/A tomography in reflection mode via the measurement of the difference frequency wave generated by a parametric array, and (3) the C-scan imaging of B/A via the measurement of the echo second-harmonic signal. A theoretical analysis and the experimental imaging of normal and pathological biological tissues by using these methods are also present and discussed. Results show that using the acoustic nonlinearity parameter imaging we can more easily distinguish the diseased tissue from the normal one than using the linear acoustic parameters. 相似文献
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I.IntroductionUltrasonicimaginghasbcenwide1yusedinthcfie1dofclinicaldiagnosis,becauseitcanvisualizethetissuetharacterizationandinternalstructureofbiologicalobjectsbyacousticwave.Usingconventionalultrasonicimagingtechnique,theimagesofacousticlinearparameterssuchassoundve1ocity,acousticimpedenccandattenuationcoefficientmaybeobtained.Thesehavebecometheeffectivemethodsofu1trasonicdiagnosis.How-ever,inordertoobscrvctheearlystageofcanccr,weintendtoobtainmoreaccurateandmorecompleteinformationaboutth… 相似文献
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The acoustic nonlinearity parameter B/A describes the nonlinear features of a medium and may become a novel parameter for ultrasonic tissue characterization. This paper presents a theoretical analysis for acoustic nonlinear parameter tomography via a parametric array. As two primary waves of different frequencies are radiated simultaneously from a circular piston source, a secondary wave at the difference frequency is generated due to the nonlinear interaction of the primary waves. The axial and radial distributions of sound pressure amplitude for the generated difference frequency wave in the near field are calculated by a superposition of Gaussian beams. The calculated results indicated that the difference frequency component of the parametric array grows linearly with distance from the piston source. It therefore provides a better source to do the acoustic nonlinearity parameter tomography because the fundamental and second harmonic signals both have a near field that goes through many oscillations due to diffraction. By using a finite-amplitude insert substitution method and a filtered convolution algorithm, a computer simulation for B/A tomography from the calculated sound pressure of the difference frequency wave is studied. For biological tissues, the sound attenuation is considered and compensated in the image reconstruction. Nonlinear parameter computed tomography (CT) images for several biological sample models are obtained with quite good quality in this study. 相似文献
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Determination of the acoustic nonlinearity parameter in biological media using FAIS and ITD methods 总被引:2,自引:0,他引:2
Two methods for determination of the acoustic nonlinearity parameter B/A in biological media are presented. One is the finite amplitude insert-substitution method (FAIS), considering the influence of both the sound attenuation of samples and the diffraction of the transducer on the experimental measurement. The other is the improved thermodynamic method (ITD), based on the measurement of phase shifts in the acoustic wave due to the change of ambient pressure. The nonlinearity parameter B/A has been measured for various biological solutions and soft tissues using these two methods. Some results of dependence of B/A values on the concentration and temperature are also presented here. 相似文献
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The second harmonic generation behavior of a contacting interface has been evaluated experimentally and discussed theoretically in the light of a nonlinear interface model. Two aluminum blocks were mated together to constitute a contact interface and subjected to normal compressive loading. A 5 MHz longitudinal toneburst wave was sent to the interface in the normal direction and the transmitted wave was recorded, from which the fundamental and the second harmonic components were extracted. A nonlinearity parameter was obtained as the ratio of the second harmonic amplitude to the squared fundamental amplitude. From the measured contact pressure dependence of the transmitted fundamental amplitude, the linear and the second-order interfacial stiffness parameters were identified, which enabled the evaluation of the nonlinearity parameter based on the theoretical model. The theoretical contact pressure dependence of the nonlinearity parameter was found to be in good qualitative agreement with the experimental results. 相似文献
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非线性声波方程的传统二次谐波二阶近似解不够精确,对测量材料的非线性系数造成较大误差。利用摄动法展开非线性声波方程得到一系列非齐次偏微分方程,根据低阶解的性质拟定高阶特解的形式,通过符号计算求出高次谐波特解,对所有二次谐波成分求和最终获得二次谐波的高阶近似解。在水中开展非线性声学实验验证高阶近似解,结果表明:二次谐波相对幅度随传播距离和输入信号均呈现先增加后减小的趋势,高阶近似解即使在传播距离不太短和输入信号不太弱的宽泛条件下也能更好地吻合实验结果。得到的高阶近似解不仅弥补了现有二次谐波幅度理论公式的不足,进行非线性声学实验时还可扩展测量范围,充分利用实验数据也能提高非线性系数的测量精度。 相似文献
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Using a 19-MHz focused Gaussian beam generated by a LiNbO(3) plate with an inverted polarization layer coupled to an acoustic lens, a method to automatically measure the nonlinearity parameter B/A in liquid media is presented. A liquid sample is poured into a cylindrical cell set with a glass tube on the lens surface. The focusing source emits burst waves. A tungsten rod immersed in the sample so that the top surface is normal to the beam axis behaves as a perfect reflector. The position of the reflector to maximize the amplitude receiving the returned wave determines the sound speed c of the sample. The amplitude measurement for the waves returned from the lens-sample interface and the reflector surface leads to the determination of the density rho and attenuation coefficient alpha, respectively. Then the B/A is finally derived by summarizing the measured result of the 38-MHz second harmonic amplitude contained in the sound returned back from the reflector, together with rho, c and alpha. All these are automatically processed in a short time less than 2 min with the performance of computer controlled instruments. 相似文献
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Pulse inversion acoustic imaging is useful as it allows second harmonic imaging to be obtained with short acoustic pulses. This allows high axial resolution, but removes any overlap in the frequency spectra of fundamental and harmonic. We demonstrate pulse inversion ultrasound modulated optical tomography using an optical speckle based detection method. Inverted and non-inverted acoustic pulses combined with synchronized strobed illumination are applied to an optically scattering medium. Over the acquisition time of a camera, multiple pulses are summed and at the next frame the phase of the ultrasound is shifted by π/2 and the process repeated. Combining the two frames allows a second harmonic signal to be obtained. A reduction in linewidth is observed (DC=9.26 mm, fundamental=4.02 mm, second harmonic=2.43 mm) in line scans of optically absorbing objects embedded in a scattering medium (thickness=16 mm, scattering coefficient=2.3 mm(-1), anisotropy factor=0.938). 相似文献
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Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method 总被引:2,自引:0,他引:2
C M Sehgal R C Bahn J F Greenleaf 《The Journal of the Acoustical Society of America》1984,76(4):1023-1029
A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20 degrees to 37 degrees C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues. 相似文献