全光学光声/OCT双模态成像系统及其应用

本文提出了一种新型的全光学光声/OCT双模态成像系统。该系统利用同一个低相干迈克尔逊干涉仪即可实现非接触式光声成像和OCT于一体,系统装置结构简单,可同时获取生物组织的吸收与散射结构信息。通过模拟实验证明了该双模态成像系统的可行性及成像能力,并对活体小鼠耳朵同时进行光声/OCT成像测试,实验结果表明非接触式光声/OCT双模态成像系统可以实现生物组织内的微血管及散射结构的高分辨率成像。进一步地,我们将光声/OCT双模态成像系统应用于基底细胞癌的检测中,获得了初步的研究结果,表明了该系统在皮肤肿瘤诊断中的具有潜在的应用价值。     

利用散射光声微分成像技术实现弱吸收物质显微成像

光声显微成像技术依赖于样品的内源性光吸收,对强散射弱吸收样品成像效果差,甚至无法进行成像。为了实现强散射弱吸收高透明生物样品的光声显微成像,以及获得图像的边缘增强效果,使光声显微成像技术在实际的生物医学研究中更有应用价值,本文首次将散射光声技术引入到光声微分显微技术中,研制了新型的散射光声微分成像技术。该技术不仅可以获得强散射弱吸收高透明生物样品的散射光声显微图像,还可以获得对应的边缘清晰的散射光声微分图像,对在生物医学研究领域有重要的应用意义。     

关于动物组织声速频散的进一步研究

80年代以来,超声组织定征(Ultrasonic Tissue Characterization)已成为超声生物物理学研究中一项前沿课题.其明显的应用背景是寻求新的超声诊断参量,以开拓定量超声诊断的新途径.所谓超声组织定征,系指研究组织的各种声学参数(如声速、频散、声阻抗、声衰减、散射及非减性参量B/A等)的量值与组织状态之间的关系及相应的测试方法.近年来我们在这一领域已做了一系列研究工作.     

人体内软组织声衰减测量方法

研究人体内各种不同的测量技术,都是为了提供软组织性质的定量信息。超声衰减是组织表征最重要的参数之一。早先在发展超声脉冲回声技术时,人们就认识了从病变区反射超声振幅的衰减能用于提示病灶的性质,衰减程度被用于识别“囊肿”和“实质性肿块”。一般充满液体的囊肿对超声衰减不大,因此有后方回声,在组织中由于诊断仪TGC的影响,显示出比周围组织更高的振幅(声像图显示为后方回声增强)。从对标本或体内肝脏声衰减的测量,可发现肝硬化中的酒精肝的声衰减比正常肝组织的要大50％左右。各种脏器的病变或肿瘤在声像图上显示后方回声的增强或后方声影,     

基于光谱编码的血管内光声组分成像

光声成像突破了传统的光学成像和超声成像在生物组织成像领域的困境,该技术基于光声(Photoacoustic,PA)效应,脉冲激光激励下的生物组织产生超声信号,超声信号被接收后,通过反投影算法将其携带的时间信息和强度信息转化为能够反映生物组织吸收结构和分布的可视化图像。基于不同生物组织的光吸收差异,当激发光强度均匀且稳定时,光声成像反映的就是该物质对于该波长光的吸收特性。本文中,我们基于导管式的血管内光声断层扫描平台结合多波长激发的光声成像算法开发了基于光谱编码的血管内光声组分成像系统,实现了在离体血管斑块中脂质组分的定量成像,高分辨获得了脂质核心的大小形态和边界信息,表征了斑块内的脂质相对含量。     

光声成像及其在生物医学中的应用

光声成像是一种新近迅速发展起来、基于生物组织内部光学吸收差异、以超声作媒介的无损生物光子成像方法,它结合了纯光学成像的高对比度特性和纯超声成像的高穿透深度特性的优点,以超声探测器探测光声波代替光学成像中的光子检测,从原理上避开了光学散射的影响,可以提供高对比度和高分辨率的组织影像,为研究生物组织的结构形态、生理特征、代谢功能、病理特征等提供了重要手段,在生物医学临床诊断以及在体组织结构和功能成像领域具有广泛的应用前景.对光声成像技术的机理、光声成像技术和方法、光声图像重建算法以及光声成像在生物医学上的应用情况作一个简单介绍,希望有助于推动我国在该领域的科研和开发应用工作的迅速发展.     

声衰减测量法对人体内软组织的应用

一、声衰减测量中几个误差的原因及其修正 按目前超声诊断仪器情况,用各种方法在各种条件下测量体内软组织的声衰减,常会受到各种干扰而引入测量误差,必须作相应的修正。其误差源主要有:1)衍射效应;2)相位相消效应;3)镜像反射效应;4)时间增益控制;5)聚焦效应;6)对数压缩等等。如衍射效应如果不修正,造成的误差可达30％。 1.衍射效应 衰减效应是衍射效应(超声场的不均匀     

用于超声造影的微囊藻气囊提取新方法

气囊是一种由蛋白质外壳包裹气体形成的纳米级细胞结构,常见于蓝藻和嗜盐古菌中.气囊中包含的气体在超声波作用下,能够散射声波并产生谐波信号而增强信噪比,具备成为新型超声造影剂的潜质.但目前提取气囊的方法主要是传统的高渗裂解法,该操作过程烦琐、得率低,不适用于气囊的大规模提取.针对这些技术瓶颈,文中建立了一种快速、高效的微囊...     

窄等离子体吸收谱线宽度的纳米金锥用于光声成像

无损光声成像技术结合了纯光学成像高选择特性和纯超声成像中深穿透特性的优点,克服了光散射限制,实现了对活体深层组织的高分辨、高对比度成像。该成像技术对内源物质例如脱氧血红蛋白、含氧血红蛋白、黑色素、脂质等进行成像,提供了活体生物组织结构和功能信息,已经在生物医学领域表现出巨大的应用前景。然而,很多与病理过程相关的特征分子的光吸收能力较弱,在活体环境中难以被光声成像系统所识别,从而限制了光声成像技术的应用范围。基于功能纳米探针的光声成像-光声分子成像极大拓展光声成像的应用范围,可以在活体层面对病理过程进行分子水平的定性和定量研究,将为实现目标疾病的早期诊断提供强大的技术支持。本文发展在近红外具有窄吸收线宽(半高宽仅为60 nm)的纳米金锥作为新型的光声探针。通过选择不同径长比的纳米金锥,可以任意调节纳米金锥的吸收峰。通过调谐激光器的波长,可实现对不同吸收峰纳米金锥的选择性激发。纳米金锥将有可能用于多光谱光声成像,实现对不同靶标的目标分子探测。     

生物组织散射元平均间距估计的一种新方法

生物组织散射元平均间中划描述生物组织微观结构特性和生物组织超微散射特性的重要参数。本文在对生物组织超声背向散射随机模的基础上,提出了基于生物组织超声背向散射信号突变点检测的工用射元平均间距估计的新方法。该方法是生物组织超声散射分析的有效方法。     

Scattering of ultrasound in cancellous bone: predictions from a theoretical model

An understanding of the interaction between acoustic waves and cancellous bone is needed in order to realize the full clinical potential of ultrasonic bone measurements. Scattering is likely to be of central importance but has received little attention to date. In this study, we adopted a theoretical model from the literature in which scattering was assumed to be proportional to the mean fluctuation in sound speed, and bone was considered to be a random continuum containing identical scatterers. The model required knowledge only of sound speeds in bone and marrow, porosity, and scatter size. Predicted attenuation, broadband ultrasonic attenuation (BUA) and backscatter coefficient were obtained for a range of porosities and scatterer sizes, and were found to be comparable to published values for cancellous bone. Trends in predicted BUA with porosity agreed with previous experimental observations. All three predicted acoustic parameters showed a non-linear dependence on scatterer size which was independent of porosity. These data confirm the value of the scattering approach and provide the first quantitative predictions of the independent influence of structure and porosity on bone acoustic properties.     

Real-Time Determination of Structural Changes of Sodium Caseinate-Stabilized Emulsions Containing Pectin Using High Resolution Ultrasonic Spectroscopy

The interactions that lead to structure transitions in oil-in-water emulsions were investigated using high-resolution ultrasonic spectroscopy. High methoxyl pectin (HMP) was added to the emulsions at various concentrations and the dynamics of aggregation induced by changes in pH were observed. Two independent ultrasonic parameters, velocity and attenuation, were measured as a function of time or pH. At pH 6.8, both velocity and attenuation of sound changed as a function of HMP concentration. During acidification, caused by the addition of glucono-δ-lactone, there were small changes in the overall ultrasonic velocity, but it was possible to relate these changes to the structural changes in the emulsion. The values of ultrasonic attenuation decreased at high pH with increasing amount of HMP, indicating changes in the flocculation state of the oil droplets caused by depletion forces. During acidification at pH 5.4, emulsions containing HMP showed a steep increase in the ultrasonic attenuation, and this pH corresponds to the pH of association of HMP with the casein-covered oil droplets. The adsorption of HMP onto the interface causes a rearrangement of the oil droplets, and the emulsions containing sufficient amounts of HMP no longer gel at acid pH. This is well described by the ultrasonic attenuation changes in the various emulsions. This research demonstrated for the first time that ultrasonic spectroscopy can be employed for in situ monitoring and analysis of acid-induced destabilization of food emulsions.     

Independent scattering model and velocity dispersion in trabecular bone: comparison with a multiple scattering model

Speed of sound measurements are used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured; this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite cylinders immersed in a saturating matrix and to derive the physical determinants of velocity dispersion. An original homogenization model accounting for the coupling of independent scattering and absorption phenomena allows the computation of phase velocity and of dispersion while varying bone properties. The first step of the model consists in the computation of the attenuation coefficient at all frequencies. The second step of the model corresponds to the application of the general Kramers–Kr?nig relationship to derive the frequency dependence of phase velocity. The model predicts negative values of velocity dispersion in agreement with experimental results obtained in phantoms mimicking trabecular bone. In trabecular bone, only negative values of velocity dispersion are predicted by the model, which span within the range of values measured experimentally. However, the comparison of the present results with results obtained in Haiat et al. (J Acoust Soc Am 124:4047–4058, 2008) assuming multiple scattering indicates that accounting for multiple scattering phenomena leads to a better prediction of velocity dispersion in trabecular bone.     

Solvent viscosity effects on protein dynamics studied by ultrasonic absorption

Solvent viscosity is known to play an important role in the kinetics of biochemical reactions, and has been suggested to modulate the dynamic structure of proteins. The effect of viscous cosolvents, of various molecular sizes, on the apparent ultrasonic absorption of bovine serum albumin in solution, at 37 degrees, has been measured in attempt to investigate the following phenomena: 1) The predicted modulating effect of viscous cosolvents on the "internal friction" of proteins, and 2) Possible differences between the microscopic and macroscopic pictures of the solvent viscosity concerning the proposed effect. We have found that A) The absorption of ultrasound (3-17 MHz) by the protein increases with increasing the cosolvent concentration. B) That increase correlates with the solvent viscosity for small cosolvent molecules, but not with macromolecular cosolvents, and C) Dextran solutions with the same concentration by weight, reveal similar ultrasonic absorption, in spite of large differences in their viscosity. A possible explanation is discussed.     

实验探索非靶组织光学参数对超声调制光的影响

生物组织是一种复杂的多层高散射介质,探索光在超声作用下的生物组织中的传播规律是超声调制光学成像术必须解决的一个基本问题,关系到最终进行图像处理与重建。通过实验探索超声调制光信号在双层和三层组织中的传播规律。实验结果表明非靶组织的光学属性（吸收系数和散射系数）和组织结构（单层或多层）都不影响超声调制光信号的调制深度。调制深度只与超声焦区介质（即靶组织）的声光属性有关,具有较佳的抗干扰性,适合用于图像重构。     

Stridulation of the clear-wing meadow katydid Xiphelimum amplipennis,adaptive bandwidth

Rubbed wings, analysed calls and a peculiar sound generator structure in males of a conocephaline katydid, Xiphelimum amplipennis, give insight into the making of broadband spectra. High shear forces are indicated by a robust forewing morphology. Intensity is high for frequencies in a 20–60 kHz ultrasonic band. Besides a typical katydid sound-radiating mirror and harp, this insect has a long costal series of semi-transparent specular sound radiators. These wing cells are loaded behind by an enlarged and partitioned subwing air space. Calls repeat steadily with five different time domain sound elements. Distinctive spectra are associated with two of these, giving stepwise frequency modulation that combines to create the exceptionally wide spectral breadth. Broadcast sound levels at 10 cm dorsal, right and left, are near 100 dB. Costal wing-cell sound radiation was explored by loading the costal “speculae” with wax. This produced almost no decrease in lateral sound levels, but did alter spectral content. Apparently, this insect’s costal region both baffles and radiates. The species lives at high densities in cluttered vegetation and sound signal attenuation should code via spectral shape for distance ranging.     

Size determination of red blood cell aggregates induced by dextran using ultrasound backscattering phenomenon.

Different methods are commonly used to study the red blood cell aggregation phenomenon. The major interest of the ultrasonic method presently discussed is to assess the mean size of red blood cell (RBC) aggregates by measuring ultrasonic intensity backscattered by blood. Applying Rayleigh theory of sound to blood medium, one can show that the scattered ultrasonic intensity is proportional to the 6th power of the size of the RBC aggregates. The ultrasonic method is used to evaluate the mean size of RBC aggregates induced by dextrans. RBCs are suspended at various hematocrits H, in solution of dextrans of different molecular weights M and at different weight concentrations Cw. Results are presented by using the ultrasonic backscattering coefficient chi which is a relevant quantity in a scattering experiment. For suspensions of RBCs aggregated with dextran of molecular weight 70,000 dalton (dextran 70) at concentration Cw = 40 g/l, variations of chi as a function of H are similar to those obtained for normal blood. At a fixed hematocrit, variation of chi versus Cw for dextran 70 exhibits a maximum at 40 g/l. In the case of RBCs suspended at hematocrit 20% and aggregated with dextrans of molecular weight M, 70,000 less than or equal to M less than or equal to 2,000,000, the variations of chi versus molar concentration Cm are similar to those of the microscopic aggregation index defined by Chien (1). Finally, a statistical model of the blood structure previously described (2) is applied to evaluate the mean size of the aggregates. According to this model, the mean size of aggregates is independent of hematocrit for H less than or equal to 40% and independent of the molecular weight of dextran for M greater than or equal to 150,000 dalton.     

白鱀豚额隆声衰减和声速的测量

本文用水浴法测试了白鱀豚额隆切片标本沿体轴方向的声压衰减系数和声速。实验表明额隆内有若干点声衰减为负值及零值、意味着声波沿这些点传输时、声压非但不减小反而增大了。再将这些点连接起来看、恰巧和从左、右鼻栓到头前部的水之间的声传输相一致、这两条途径看起来有点像小声道似的。     

Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks.     

Influence of absorption on polarization effects in light scattering from human red blood cells

Polarization effects in light scattering are sensitive indicators of cell structure and structural changes in time. In the spectral regions where the optical properties of the scatterers are relatively constant, the scattering pattern scales, it contracts or expands in a predictable manner as a function of the wavelength. In the spectral regions where the optical properties are strongly wavelength dependent (near absorption bands, etc.) the scattering curves do not scale, but change drastically in phase and amplitude as the wavelength is varied. Reported here is an empirical study of the magnitude of the influence of absorption on the polarization effects in light scattering. Scattering curves have been obtained for human red blood cells in the absorption band (blue light) and far from the absorption band (red light). The scattering at these wavelengths shows very strong nonscaling differences. These observations suggest the use of polarization effects in light scattering and their wavelength dependence for the studies of structural changes in cell nuclei. Nucleoproteins have strong absorption, optical rotatory dispersion and circular dichroism bands in the ultraviolet region of the spectrum, whereas there is little ψ-dependence in the visible range. There is also the possibility of binding specific chromophoric dyes to cell components, thus introducing absorption bands in the visible range, where scattering instrumentation and laser light sources are more readily available.