Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction

Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.     

Random phase screen influence of the inhomogeneous tissue layer on the generation of acoustic vortices

The influence of the inhomogeneous tissue layer on the generation of acoustic vortices(AV) is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phase screen, the formula of acoustic pressure for the AV beam generated by a circular array of eight planar piston sources is derived. With the actual correlation length of the abdominal wall, numerical simulations before and after the insertion of the inhomogeneous tissue layer are conducted, and also demonstrated by experimental measurements. It is proved that, when the thickness variation of the phase screen is less than one wavelength, no significant influence on the generation of AVs can be produced. The variations of vortex nodes and antinodes in terms of the location, shape, and size of AVs are not obvious. Although the circular pressure distribution might be deformed by the phase interference with a larger thickness variation, AVs can still be generated around the center axis with perfect phase spirals in a reduced effective radius. The favorable results provide the feasibility of AV generation inside the human body and suggest the application potential of AVs in object manipulation for biomedical engineering.     

球形集声器在生物组织中形成的组织损伤

球形集声器可在亚波长焦域内形成高强度声压,在高强度聚焦超声治疗中具有潜在应用前景.本文结合非线性声传播理论及生物传热学理论,研究球形集声器在生物组织中形成的组织损伤.实验中采用430 kHz,内径为240 mm的球形集声器对肝组织作用,结果表明:集声器表面声压为53 kPa时作用2 s,可以形成小于波长尺度的组织损伤.理论计算结果与实验结果符合得较好,并且理论模型可优化球形集声器的开口孔径.研究结果表明,球形集声器可应用于肿瘤的精细超声治疗.     

Beam alignments based on the spectrum decomposition of orbital angular momentums for acoustic-vortex communications

Given the enhanced channel capacity of wave chirality, acoustic communications based on the orbital angular momentum (OAM) of acoustic-vortex (AV) beams are of significant interest for underwater data transmissions. However, the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding. To avoid the required multiple measurements of the traditional orthogonality based algorithm, the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays. Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays. To achieve an ideal arrangement, two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum (SD-OAM). By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers, accurate beam alignments are accomplished by multiple adjustments in three dimensions. The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams. The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays, and suggest more application potentials for acoustic communications.     

In vivo hyperthermia effect induced by high-intensity pulsed ultrasound

Hyperthermia effects (39-44°C) induced by pulsed high-intensity focused ultrasound (HIFU) have been regarded as a promising therapeutic tool for boosting immune responses or enhancing drug delivery into a solid tumor. However, previous studies also reported that the cell death occurs when cells are maintained at 43°C for more than 20 minutes. The aim of this study is to investigate thermal responses inside in vivo rabbit auricular veins exposed to pulsed HIFU (1.17 MHz, 5300 W/cm2 , with relatively low-duty ratios (0.2%-4.3%). The results show that: (1) with constant pulse repetition frequency (PRF) (e.g., 1 Hz), the thermal responses inside the vessel will increase with the increasing duty ratio; (2) a temperature elevation to 43°C can be identified at the duty ratio of 4.3%; (3) with constant duty ratios, the change of PRF will not significantly affect the temperature measurement in the vessel; (4) as the duty ratios lower than 4.3%, the presence of microbubbles will not significantly enhance the thermal responses in the vessel, but will facilitate HIFU-induced inertial cavitation events.     

基于超声RF信号的甲状腺结节智能诊断方法*

由于人口老龄化的原因,甲状腺癌的发病率增长率在所有癌症中是最为显著的。因此,对存在癌变可能的甲状腺结节进行预检查显得尤为重要,而超声智能诊断系统在甲状腺结节早期筛查方面已展现出巨大的应用前景。该文的工作旨在提出一种基于超声原始射频信号的组织参数定征和人工神经网络相结合的甲状腺结节智能诊断方法,以提高临床超声诊察效率及准确性。为达成上述目的,该文使用滑动窗口图像分析方法和多兴趣区覆盖的方法提取组织定征参数作为特征,使用人工神经网络进行良恶性分类,并对可能影响分类准确性的相关因素进行参数相关性分析。结果显示,基于临床样本,该文提出的智能诊断方法可达到93.2%敏感度、94.0%特异性和93.5%准确率。该方法一定程度上克服了传统方法无法充分利用图像局部细节信息的不足,有效提高了诊察效率和准确性;另一方面,与深度神经网络相比,本方法对计算资源和样本量的需求较少。因此有望在该文研究基础上最终建立一套可实际用于甲状腺结节的预筛查的临床智能诊断系统。     

低强度脉冲超声激发的声微流增强藻酸钙凝胶支架材料的孔隙率和通透性研究

低强度脉冲超声(LIPUS)激发的声微流场所产生的剪切应力可作用于细胞膜表面,从而显著增强细胞膜的通透性。构建了三维藻酸钙凝胶支架培养系统,来模拟有利于细胞生长的营养供给和新陈代谢体内微环境;基于扫描电子显微镜、体内荧光图像和激光共聚焦图像观测技术,对LIPUS增强三维藻酸钙凝胶支架材料的孔隙率和通透性的作用机制和参数相关性进行了系统的研究。结果表明,三维藻酸钙凝胶支架材料的孔隙率和通透性可随着LIPUS的驱动声压的升高而显著增强。此外,通过对三维支架材料内的细胞增殖情况分析,发现在适当的LIPUS驱动声压(如P-=0.055 MPa)下,HeLa细胞在LIPUS作用下的三维藻酸钙凝胶支架材料中可获得更高的增殖率。      

水波孤子起始不稳定性的实验研究

系统地测量了小宽度的矩型水槽中的自调制（０，１）模孤波起始不稳定性与液体深度、水槽宽度、混合液体中甘油体积比等因素之间的关系。实验发现液体深度、容器宽度的减小及混合液体中甘油体积比的增加都会导致起始激励加速度的变大并引起一定的频移。实验结果与理论计算达到了令人满意的定性相似。     

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.