调频激励增强微气泡的次谐波理论和实验研究

超声造影剂的次谐波成像可以提高造影组织比，提供更好的图像质量. 提出一种利用调频脉冲激励以增强造影剂微气泡产生的次谐波新方法. 基于修正的Church方程，从理论上讨论了次谐波的产生与调频激励声压的关系及产生阈值，并且实验证实了优化调频信号的带宽及调频时间可以提高次谐波信号幅度及改善主瓣和旁瓣特性. 理论与实验表明，与传统脉冲信号激励相比，调频信号激励产生的次谐波幅度可提高约22dB. 关键词： 调频激励 超声造影剂 微气泡 次谐波     

准高斯声束对超声造影剂的声辐射力研究*

超声造影剂的定向输运在超声医学成像领域有着极为重要的意义,而声辐射力作用是实现该过程的关键,相比于高斯声束,准高斯声束是无源亥姆霍兹方程的精确解,可以使用标准波分解法简化计算。因此,本文研究了准高斯声束对超声造影剂的声辐射力作用。文章首先分析了准高斯声束与高斯声束之间的相关性;随后通过数值计算求得了准高斯声束对超声造影剂模型的声辐射力函数与无量纲频率之间的关系;最后,本文研究了不同造影剂气泡情况下的声辐射力。研究结果表明:声辐射力函数随无量纲频率变化将在不同位置出现共振峰,不同的波束宽度值将改变辐射力强度,但不改变共振峰的位置。相关结果可为利用声辐射力定向输运超声造影剂至靶向位置提供理论参考。     

包膜黏弹特性及声驱动参数对相互作用微泡动力学行为的影响

关于多气泡相互作用的理论研究对于深入理解超声造影剂在医疗领域中的应用机理具有重要意义。本工作建立了一个2维轴对称有限元模型来研究流体环境中超声造影剂双气泡相互作用,讨论了驱动超声频率和气泡尺寸对气泡之间吸引和排斥趋势的影响,得到了气泡半径与气泡之间距离随时间变化的曲线,以及气泡周围流体速度场的细节,并且研究了气泡包膜参数(即表面张力系数和粘度系数)对气泡相互作用的影响.结果表明,相互作用中的气泡对整体的相对运动趋势由驱动频率和共振频率之间的关系决定;在超声参数固定时,气泡包膜的粘弹特性可用来调控气泡间相互作用强度。结果对实验中观察到的气泡聚集现象进行了合理解释,并为超声造影剂在医疗实践中的应用提供了基础理论支撑.      

脉冲占空比对磁性微泡介导的聚焦超声温升效应的影响

集合多种诊断和治疗功能的声/磁造影剂微泡的研究与开发已经成为当前医学超声、生物医学工程及临床应用领域共同关注的热点问题.超顺磁氧化铁纳米颗粒具有独特的磁性特征和良好的生物相容性,可被用作核磁共振造影剂来提升影像对比度、空间分辨率及临床诊断准确性.我们的前期工作表明,通过将超顺磁氧化铁纳米颗粒挂载于常规超声造影剂微泡表面,可以成功构建多模态诊断及治疗介质,显著改变超声造影剂微泡的尺度分布及包膜粘弹系数等物理特性,进而影响微泡造影剂的声散射特性及其声空化效应和热效应.然而,此前的研究仅考虑了声场强度和微泡浓度等影响因素,对于脉冲超声时间特性对磁性微泡造影剂动力学响应的影响的相关研究仍有所欠缺.本文通过热电偶对凝胶仿体血管模型中流动的双模态磁性微泡在不同占空比超声脉冲信号作用下,产生温升效应开展了系统的实验测量,并基于有限元模型对实验结果进行了仿真验证.结果显示,脉冲信号占空比的提升是增强血管中磁性微泡在聚焦超声作用下温升效果的关键性时间影响因素.本文的研究成果将有助于更好地理解不同超声作用参数对双模态磁性微泡的热效应的影响机制,对保障双模态磁性微泡在临床热疗应用中的安全性和有效性具有重要的...     

基于调频信号发射的超声造影剂谐波成像方法

提出了一种能够提取超声造影剂回波中二次谐波的非线性成像方法,从数学原理、仿真计算和声学实验三个方面对造影剂血流灌注成像方法进行了研究。首次将调频信号发射技术用于医学超声造影剂谐波成像领域,仿真计算和声学实验结果表明:为了获得较好的图像质量,发射调频信号应该具有合适的包络;发射信号带宽与解码匹配滤波器带宽之间必须有一个带宽间隔;适当降低发射声压能够降低生物组织的谐波。应用编码发射方法和解码滤波器,得到了造影剂二次谐波图像,此图像具有较好的信号噪声比和造影剂组织比。声学实验结果和理论计算结果完全吻合。     

超声造影剂微泡非线性动力学响应的机理及相关应用

随着生命科学及现代医学的发展, 一体化无创精准诊疗已经日益成为人们关注的焦点问题, 而关于超声造影剂微泡的非线性效应的相关机理、动力学建模及其在超声医学领域中的应用研究也得到了极大的推动. 本文对下列课题进行了总结和讨论, 包括: 1)基于Mie散射技术和流式细胞仪对造影剂微泡参数进行定征的一体化解决方案; 2)通过对微泡包膜的黏弹特性进行非线性修正, 构建新的包膜微泡动力学模型; 3)探索造影剂惯性空化阈值与其包膜参数之间的相关性; 以及4)研究超声联合造影剂微泡促进基因/药物转染效率并有效降低其生物毒性的相关机理.     

超声分子成像进展

超声分子成像在超声医学成像的基础上,利用靶向超声造影剂为分子探针,以可视化和定量获取活体组织细胞的分子信息为目标的影像术。它不用进行手术活检,不仅可以给出病灶的空间信息,而且能确定它的性质,进行针对性的治疗和对疗效进行评估。本文对现有的核医学分子成像,磁共振分子成像,光学分子成像和光声分子成像技术作了简单介绍,着重讨论了超声分子成像技术和应用的进展。     

高斯型超声换能器及其线性与非线性声场

本文介绍了一种具有独特性能的高斯型声场。声场的分析包括线性与非线性。同时对产生这种高斯型声场的高斯型超声换能器的当前研究也作了介绍与评述。文章也指出了高斯型换能器在超声检测中的应用前景。     

用于磁共振成像对比增强的造影剂研发进展

介绍了磁共振成像造影剂的作用原理与性能, 对用于造影剂的钆螯合物和自由基、超顺磁性氧化铁粒子的研究与开发进展作了综合评述.     

无造影剂增强的超快超声脊髓微血管成像方法

微小血管及其血流实时成像对监测生物体血氧代谢等具有重要意义.在无微泡造影剂的情况下,传统超声多普勒技术仍较难实现高信噪比的微小血管成像.本研究提出了一种无造影剂增强的超快超声脊髓微血管成像方法.本研究从基于多角度复合平面波的高帧频成像技术出发,提出基于特征值分解的频率-幅值双阈值滤波法,从而将脊髓组织信号和微血流信号分离,可实现脊髓内微血流的动态成像.在体成像实验结果表明,无超声造影剂时,超快超声多普勒成像技术仍可获得较为清晰的大鼠脊髓内微血流的实时图像,并能够清晰地呈现脊髓受损所致的微血流缺失状况.定量分析结果表明,增大复合平面波角度数可有效提高图像的信噪比.综上,超快超声多普勒成像技术有潜力被应用于脊髓内微血管成像及功能实时监测与动态评价,相关结果可为脊髓功能成像方法的研究提供借鉴.     

五氯苯酚分子在激发和电离过程中分子结构和简谐振动的变化研究

利用密度泛函理论(DFT)计算得到了五氯苯酚(PCP)分子在基态(S₀态)、第一电子激发态(S₁态)和离子基态(D₀态)优化的结构参数和简谐振动频率值.通过分析PCP分子在激发和电离过程中的苯环与取代基OH和Cl之间的键长和键角的变化情况，可以看到取代基OH和Cl的给电子和吸电子效应使苯环的结构发生了变化，尤其是靠近Cl原子处的变化较明显.通过分析每个简谐振动模式对应的振动频率值在激发和电离过程中的变化情况，可以看到PCP分子在S₀态和D₀态的同一振动模式对应的振动频率值接近，在S₁←S₀跃迁中，PCP分子中约二分之一的平面内弯曲和平面内伸缩振动受到的影响较大，而平面外弯曲振动受到的影响较小.     

The ⋆-value equation and Wigner distributions in noncommutative Heisenberg algebras

We consider the quantum mechanical equivalence of the Seiberg-Witten map in the context of the Weyl-Wigner-Groenewold-Moyal phase-space formalism in order to construct a quantum mechanics over noncommutative Heisenberg algebras. The formalism is then applied to the exactly soluble Landau and harmonic oscillator problems in the 2-dimensional noncommutative phase-space plane, in order to derive their correct energy spectra and corresponding Wigner distributions. We compare our results with others that have previously appeared in the literature.Dedicated to Mike Ryan on his sixtieth birthday, who as a scientist always understood that it is nice to be good, but that it is better to be nice.     

Imaging through a bundle of square cross-section fibers: The dependence of image contrast on the bundle parameters

A very simple formula for the image contrast dependence on the parameters of the imaging bundle of square cross-section fibers is derived for both ideally insulated and cross-talking fibers.     

A new formula to calculate Franck-Condon factors for displaced and distorted harmonic oscillators

A new formula has been derived to calculate Franck-Condon factors for two harmonic oscillators with different equilibrium positions and different vibrational frequencies. The derivation is simple and straightforward, and a new expression for calculating the matrix element 〈v|xⁿ|v′〉 has also been derived.     

Harmonic generation in superconducting Bi(Pb)SrCaCuO thick films

We present a detailed study of harmonic generation in Bi(Pb)SrCaCuO superconducting thick film prepared by screen printing technique. A comparative study of amplitude of harmonics of two films of different J_c have been carried out. The variation of amplitudes of the harmonics are studied as a function of magnitude of ac and dc field. The temperature dependence of amplitude of third harmonic (V³) is studied with increasing amplitude as well as frequency of ac field. These results are analyzed in the frame work of critical state model. V₃ -T curve also indicates the presence of two phases in Bi(Pb)SrCaCuO film.     

1-D harmonic oscillator in MONDified inertia

In this paper we study the dynamics of a harmonic oscillator with laws of motion prescribed by MOND (Modified Newtonian Dynamics) in its modified inertia formulation. A differential equation for a 1D harmonic oscillator is obtained and several features of its solution are analyzed. Particular attention is given to the deep MOND limit regime, where the equations of motion are significantly different from the Newtonian one.     

Improved analysis of the electrically manifested distortions of condenser microphones

An improved analysis for the electrically manifested nonlinear distortions in condenser microphones is presented. The analysis shows that in typical condenser microphones excited by multisinusoidal sound signals, the second-order intermodulation components of frequencies ω_r±ω_s will be dominant. This result suggests that, rather than using the total harmonic distortion (THD), the use of the standard two- or three-tone tests for measurement of the nonlinear performance of condenser microphones would be more reliable and sensible.     

Modelling harmonic generation measurements in solids

Harmonic generation measurements typically make use of the plane wave result when extracting values for the nonlinearity parameter, β, from experimental measurements. This approach, however, ignores the effects of diffraction, attenuation, and receiver integration which are common features in a typical experiment. Our aim is to determine the importance of these effects when making measurements of β over different sample dimensions, or using different input frequencies. We describe a three-dimensional numerical model designed to accurately predict the results of a typical experiment, based on a quasi-linear assumption. An experiment is designed to measure the axial variation of the fundamental and second harmonic amplitude components in an ultrasonic beam, and the results are compared with those predicted by the model. The absolute β values are then extracted from the experimental data using both the simulation and the standard plane wave result. A difference is observed between the values returned by the two methods, which varies with axial range and input frequency.     

Generation of second-harmonic radiations of a self-focusing laser from a plasma with density-transition

A Gaussian laser-beam resonantly generates a second-harmonic wave in a plasma in the presence of a wiggler magnetic-field of suitable period. The self-focusing of the fundamental pulse enhances the intensity of the second-harmonic pulse. An introduction of an upward plasma-density ramp strongly enhances the self-focusing of the fundamental laser pulse. The laser pulse attains a minimum spot size and propagates up to several Rayleigh lengths without divergence. Due to the strong self-focusing of the fundamental laser pulse, the second-harmonic intensity enhances significantly. A considerable enhancement of the intensity of the second-harmonic is observed from the proposed mechanism.     

Approximate formulae for the overlap integral of two harmonic oscillator wave functions

The use of second-order perturbation theory to derive approximate formulae for the overlap integral of two harmonic oscillator wave functions is discussed, and the results applied to the theory of intensity distributions in vibrational progressions in electronic spectra. For the vibrational progression m←0 an approximate formula is given which, when the vibrational frequencies of the initial and final states differ by less than 10%, reproduces to an accuracy of 1% or less the intensity profile calculated using the exact formulae for the overlap integrals.