利用纳米力学方法对皮肤进行超声组织定征的研究

纳米力学方法适用于具有离散特性的材料.利用纳米力学方法,得出声波在多层皮肤组织中的波动方程.分别改变黑素瘤皮肤的泊松比、黑素瘤侵袭厚度(Breslow深度)、节间距离,计算多层皮肤结构模型对垂直入射纵声波的反射系数.同时计算了声速和声衰减系数随组织参数的变化.计算结果表明,可综合利用一定频率段内反射系数最小点数、声速和衰减系数的变化来表征正常皮肤和病变皮肤.     

Ultrasound Attenuation in Biological Tissue Predicted by the Modified Doublet Mechanics Model

Experimental results have shown that in the megahertz frequency range the relationship between the acoustic attenuation coefficient in soft tissues and frequency is nearly linear. The classical continuum mechanics （CCM）, which assumes that the materiaJ is uniform and continuous, faJls to explain this relationship particularly in the high megahertz range. Doublet mechanics （DM） is a new elastic theory which takes the discrete nature of material into account. The current DM theory however does not consider the loss. We revise the doublet mechanics （DM） theory by including the loss term, and cMculate the attenuation of a soft tissue as a function of frequency using the modified the DM theory （MDM）. The MDM can now well explain the nearly linear relationship between the acoustic attenuation coefficient in soft tissues and frequency.     

基于分数导数研究高强度聚焦超声的非线性声场

在高强度聚焦超声(high intensity focused ultrasound, HIFU) 的研究中, 生物组织的衰减和色散性质会对声能量的空间分布产生影响. 本文提出应用分数导数修正非线性Khokhlov-Zabolotskaya-Kuznetsov (KZK)方程, 研究生物组织中非线性HIFU声场. 对三种生物仿体的衰减和声速色散的理论实验研究表明分数导数应用的可行性, 在此基础上通过数值仿真分析研究了衰减及声速随频率的变化对HIFU焦域分布的影响. 研究结果表明, 在计算强非线性聚焦超声时, 由于高次谐波的强色散作用, 引入分数导数来解决生物组织特殊的衰减以及色散问题可进一步提高HIFU治疗的安全性. 关键词： 分数导数 声衰减 色散 高强度聚焦超声     

Ultrasonic assessment of tissue hydration status

Tissue water content is an important diagnostic parameter that can be used for estimation of water loss in muscles such as common dehydration during high endurance exercises. It could be also applied for evaluation of the increased fluids content in the tissue caused by the variety of pathological conditions or edemas. Ultrasonic method for tissue water content monitoring is based on the premise that the speed of a bulk or compression sound wave is determined mainly by the molecular content of the tissue. Most soft tissues, including muscles that consist of about 70-80% water, exhibit shift of the ultrasound velocity associated with the change in their water content. In the present paper, we tested the feasibility of assessing changes in tissue water content by measurements of ultrasound velocity in ex vivo animal muscle tissues. An increase in the ultrasound velocity correlated with the volumetric water loss in the tissue was observed when other tissue components (proteins, fat) remained constant. Possibility to assess muscle dehydration with 1% accuracy was confirmed in model dehydration experiments, where ultrasound velocity slope of about 3 m/s per 1% of water loss was revealed at measurement error less than 2 m/s. Hence, the ultrasonic approach can provide basis for a convenient, lightweight system in sports medicine for monitoring total body hydration during long-term endurance exercise in hot conditions, as well as for edemas monitoring and other medical applications.     

Determination of biomass concentration by measurement of ultrasonic attenuation

Experimental results are presented that demonstrate that ultrasonic attenuation can be used to estimate the biomass concentration of a biological suspension. The attenuation approach avoids the temperature sensitivity of established ultrasound velocity test methods, which have hindered their application in process environments. An empirical model is presented for the estimation of the biomass of Microcystis aeruginosa suspensions based on acoustic attenuation, temperature, and frequency, and is compared with experimental results.     

Ultrasound fields in attenuating media

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas.     

高频聚焦超声声场和温度场的仿真研究

为探究临床常用的7 MHz高频聚焦超声在多层生物组织中的声传播以及毫秒级时间内的生物传热规律问题,基于Westervelt方程和Pennes传热方程,使用有限元方法建立高频聚焦超声辐照多层组织的非线性热黏性声传播及传热模型。首先分析了线性模型和非线性模型之间的差异,然后在非线性模型下探究换能器的参数对声场和温度场的影响。仿真结果显示：在7 MHz频率下,当换能器输出声功率超过5 W时,声波传播的非线性效应不可忽视(p <0.05);当声功率从5 W增大到15 W时,非线性模型与线性模型预测的温度偏差从20%增加到34.703%;高频聚焦超声波的非线性行为比低频更加显著,基频能量向高次谐波转移的程度增大,声功率为10 W和15 W时4次谐波与基波之比分别达到7.33%和12.12%;高频换能器参数的改变对组织中声场和温度场分布的影响较大,换能器焦距从12 mm减小到11.2 mm,焦点处最高温度增加了77%。结果表明,7 MHz聚焦超声的非线性声传播需要考虑到4次谐波的影响。该文提出的多层组织非线性仿真模型可为高频聚焦超声换能器参数优化及制定安全、有效的术前治疗方案提供理论参考。     

Propagation of ultrasonic waves in bulk gallium nitride (GaN) semiconductor in the presence of high-frequency electric field

The propagation of ultrasound is studied in bulk GaN semiconductor in the presence of a strong AC field oscillating at a frequency much higher than that of the ultrasound. Analytical expressions have been obtained for the attenuation coefficient (α) and the renormalised velocity (v) of the acoustic wave. It is shown that the dependencies of the ultrasonic absorption coefficient of the conduction electrons and the renormalised sound velocity on the field amplitude and the sound frequency have an oscillatory character which can be used to determine the effective mass and mobility of the material. The threshold field needed to observe the oscillation is two orders smaller than that needed in the case of CdS.     

Detection of chemical damage in concrete using ultrasound

This research deals with a non-destructive method for characterizing the degraded cover of concrete structures using high-frequency ultrasound (0.5-1 MHz). Although such a frequency range is unusual in civil engineering, it is well suited to the kind of defect to be detected, as it corresponds to a thin near-to-surface layer with increased porosity and density of microcracks. In order to assess the feasibility of detecting concrete cover degradation, velocity and attenuation measurements were made on both halves of a concrete slab. One half was immersed into an acid solution for 15-45 days, while the other half remained sound. These measurements were made for longitudinal, transverse and surface waves. The results obtained show a 23% decrease of ultrasonic pulse velocity and a 1000% increase of attenuation in the degraded material relative to the sound material. It is thus possible to detect and characterize concrete cover degradation using high-frequency ultrasound. Although attenuation measurements in heterogeneous media are difficult, their sensitivity to degradation is very high.     

除垢超声波传播影响因素的理论研究

从一维平面波理论入手分析了超声波声压分布特性。依据多普勒频移原理,在声场的运动方程,连续性方程,波动方程的基础上,建立一个超声波在流动的液体中传播的控制方程。根据轴对称模型的实际特点,简化了所得方程,并求出解析解。结果表明流动液体可以产生声波的衰减。液体的黏滞性是产生超声波衰减的重要原因。超声波的频率较高,液体的黏滞性对超声波衰减影响明显。依据黏滞力与速度梯度的关系,建立一个超声波在黏滞液体传播的控制方程,并依据边界条件求出解析解,反映了媒质黏滞性对超声波传播尤其是衰减特性的影响。     

High frequency ultrasonic characterization of human vocal fold tissue

Recently, endolaryngeal sonography at frequencies ranging from 10 to 30 MHz has been found to be useful in diagnosing diseases of the vocal folds (VFs). However, image resolution can be further improved by ultrasound at higher frequencies, necessitating the measurement of high-frequency acoustic properties of VF tissue. The ultrasonic parameters of integrated backscatter, sound velocity, and frequency-dependent attenuation coefficient were measured in both the lamina propria (LP) and vocalis muscle (VM) of human VFs using a 47 MHz high-frequency ultrasonic transducer. The integrated backscatter was -173.44+/-6.14 (mean+/-s.d.) and -195.13+/-3.58 dB in the LP and VM, respectively, the sound velocity was 1667.68+/-44.9 and 1595.07+/-39.33 ms, and the attenuation coefficient at 47 MHz was 8.28+/-1.72 and 7.17+/-1.30 dBmm. The difference between these ultrasonic parameters may be attributed to variations in the structure and fiber concentrations in VF tissue. These results could serve as a useful clinical reference for the further development of high-frequency ultrasound devices for endolarynx sonography applications.     

含红外发散的低温玻璃超声声速理论

本文采用红外发散和隧道态模型,讨论玻璃超声声速在3K温度以下的行为。我们把声速的改变看作两部分组成:无弛豫过程和有弛豫过程。前者采用“玻色型元激发”理论处理;后者采用“含红外发散的隧道弛豫”理论处理。我们不但得到与实验符合较好的声速-温度曲线,并且解释了一般频率下(10⁷Hz,T为0.3—1K),声速与频率无关的lnT规律和高频下(2GHz,T<0.1K)声速存在极小值的现象。 关键词：     

Reliability of sound attenuation in Florida scrub habitat and behavioral implications

Attenuation over distance in natural habitat is often difficult to predict when measured without respect to sound frequency. The physical-acoustic structure of Florida scrub habitat is described and both attenuation and reliability of attenuation are measured as a function of sound frequency, over several distances, speaker elevations, and microphone elevations. The spatial context of sound propagation in Florida scrub habitat is discussed and a model designed to describe contributions to overall attenuation from individual factors is presented. Sound frequencies below approximately 3.5 kHz attenuate more reliably than higher sound frequencies, suggesting that animals should pay greatest attention to relatively low sound frequencies when they assess attenuation or estimate sound-pressure level.     

Relaxation processes in harmonic glasses?

A relaxation process, with the associated phenomenology of sound attenuation and sound velocity dispersion, is found in a simulated harmonic Lennard-Jones glass. We propose to identify this process with the so-called microscopic (or, instantaneous) relaxation process observed in real glasses and supercooled liquids. A model based on the memory function approach accounts for the observation and allows one to relate to each other (1) the characteristic time and strength of this process, (2) the low frequency limit of the dynamic structure factor of the glass, and (3) the high frequency sound attenuation coefficient, with its observed quadratic dependence on the momentum transfer.     

Effect of frequency dependent processes on pulsed Doppler sample volume

The change in the frequency spectrum of ultrasound pulses as a result of frequency dependent attenuation and scatter is known to alter the spectrum of Doppler signals from blood flow parallel to the beam axis. It is shown here that the change in pulse shape accompanying this pulse spectrum change as a result of these processes, together with the velocity dispersion accompanying frequency dependent attenuation and linked to it by the Kramers-Kronig relations, will change the pulsed Doppler sample volume shape and position.     

A simulation algorithm for ultrasound liver backscattered signals

In this study, we present a simulation algorithm for the backscattered ultrasound signal from liver tissue. The algorithm simulates backscattered signals from normal liver and three different liver abnormalities. The performance of the algorithm has been tested by statistically comparing the simulated signals with corresponding signals obtained from a previous in vivo study. To verify that the simulated signals can be classified correctly we have applied a classification technique based on an artificial neural network. The acoustic features extracted from the spectrum over a 2.5 MHz bandwidth are the attenuation coefficient and the change of speed of sound with frequency (dispersion). Our results show that the algorithm performs satisfactorily. Further testing of the algorithm is conducted by the use of a data acquisition and analysis system designed by the authors, where several simulated signals are stored in memory chips and classified according to their abnormalities.     

Numerical simulation of wave propagation in cancellous bone

Numerical simulation of wave propagation is performed through 31 3D volumes of trabecular bone. These volumes were reconstructed from high synchrotron microtomography experiments and are used as the input geometry in a simulation software developed in our laboratory. The simulation algorithm accounts for propagation into both the saturating fluid and bone but absorption is not taken into account. We show that 3D simulation predicts phenomena observed experimentally in trabecular bones : linear frequency dependence of attenuation, increase of attenuation and speed of sound with the bone volume fraction, negative phase velocity dispersion in most of the specimens, propagation of fast and slow wave depending on the orientation of the trabecular network compared to the direction of propagation of the ultrasound. Moreover, the predicted attenuation is in very close agreement with the experimental one measured on the same specimens. Coupling numerical simulation with real bone architecture therefore provides a powerful tool to investigate the physics of ultrasound propagation in trabecular structures.     

管束穿孔板的管腔耦合共振吸声机理研究

为了揭示管束穿孔板共振吸声结构的吸声机理,利用热黏性条件下基于有限元算法的管束穿孔板仿真模型,研究了平面声波正入射条件下,管束穿孔板内部声场分布特征,并利用阻抗管对吸声系数的理论仿真结果进行了试验验证.结果表明,管束穿孔板在低频主要靠腔体共振吸声,在高频主要靠管共振吸声,管束穿孔板整体呈现出较为明显的管腔耦合共振吸声特征。管束穿孔板共振时管中声强和质点法向振速较大,高频次吸声峰频点处管中和腔中均有驻波形成,频率越高驻波数量越多.管束穿孔板的耦合共振受到管长、腔深、穿孔率和管内径等参数变化的影响,管长对高频耦合共振的影响最大,管长增大使高频主吸声峰频点移向低频,并使相邻主吸声峰之间的间距减小.      

Model and experimental analysis of oblique incident ultrasound in a tissue layer using doublet mechanics theory

The fundamental framework of doublet mechanics (DM) is used to analyze high-frequency ultrasound wave propagation in materials with discrete microstructure. Ultrasonic reflection coefficients were measured from a thin layer of tissue embedded between two glass substrates at oblique incidence. Theoretical calculations for the reflection coefficients of a multi-layered system at oblique angles are performed using both DM theory and the classical continuum mechanics theory (CCM). For example, at the frequency of 10 MHz at incident angle 8° in sample with 30 μm thickness, the discrepancy in the magnitude of the reflection coefficient between experimental results and theoretical prediction is 15.8% for DM but 79.0% for CCM; similar results at other frequencies and incident angle in the samples with 30 and 60 μm thickness have also been obtained, which demonstrates that the DM theory can better describe the wave propagation in tissue. The influence of the incident angles and tissue thickness are also discussed in this paper.     

warping变换提取单模态反演海底衰减系数

为了获得浅海海底地声模型参数,利用warping变换方法分离出单模态简正波.对于接收深度固定、定深爆炸声源情况,以简正波理论为基础定义了距离归一化的简正波传播损失,并且其随传播的距离呈线性关系,故可通过此变化规律得到声压值实部的衰减因子,进而可求得海底地声模型参数:海底衰减系数.为验证此方法的有效性,仿真了warping变换提取单模态简正波的过程,同时将warping变换提取的单模态简正波与数值计算的结果进行比较验证;并针对某次黄海试验数据进行了处理,得到在150—550 Hz频带范围内海底衰减随频率的变化规律为α=0.581f_k~(1.86)(dB/m).通过与其他学者在相同海域试验结果的对比验证,变化规律基本相同.此外不同模态间反演相同频点的衰减系数接近也较好地支撑了结果.