基于矢量阵的运动声源柱面聚焦定位方法试验研究

本文基于被动合成孔径原理, 在建立运动声源矢量阵近场柱面聚焦测量模型的基础上, 分别研究了适用于单频线谱信号和宽带连续谱信号的矢量阵柱面聚焦定位方法, 通过数值仿真计算了该方法在多种误差条件下的定位精度, 并进一步通过舱段模型试验对该方法的工程实用性和正确性进行了详细的分析和论证. 舱段模型试验结果表明, 柱面聚焦定位结果与壳体振动能量分布规律符合较好, 该方法不仅能真实反映声源位置信息, 而且能反映不同频带内声源能量分布的相对大小, 具有良好的定位效果.     

一种适用于超声多普勒血流速度测量的混沌调频连续波的研究

虽然脉冲多普勒系统测量血流速度时,能够确定距离,但可测速度范围受频率混淆限制,同时多普勒信号的信噪比差．连续波多普勒系统提供了较高的多普勒信号的信噪比,并没有可测速度限制,但无法提供距离信息．线性调频及正弦调频连续波测量系统,能够提供拥有距离信息的高信噪比多普勒信号,同时杂波功率低,但由于多普勒信号频谱具有周期性,存在一定的距离模糊．针对存在的问题,提出基于混沌调频连续波的超声多普勒血流速度测量方法,它不仅具有较高的信噪比,而且由于多普勒信号频谱无周期性,因此不存在距离模糊．经过原理分析及仿真实验,验证了混沌调频连续波的有效性．     

术前超声双重造影检查对胃癌患者胃周淋巴结转移的评估价值

目的探讨超声双重造影检查（DCUS）在不同部位胃癌术前淋巴结转移评估中的应用价值。方法选择180例胃癌患者,手术前3～5d内均进行DCUS及螺旋CT检查,对不同部位的胃癌患者术前均进行淋巴结分站评估,与术后病理检查结果对照得出正确率,并进行相互间比较。结果 DCUS和螺旋CT检查对远端胃切除患者淋巴结转移判断正确率分别为86.0%和83.9%,对全胃切除患者的判断正确率分别为82.5%和85.0%,两种检查方法判断准确率差异均无统计学意义（P＞0.05）;DCUS对近端胃切除患者淋巴结转移判断正确率为66.0%,明显低于螺旋CT检查的85.1%,差异有统计学意义（均P＜0.05）。结论胃癌术前淋巴结转移评价中,超声双重造影检查判断正确率与螺旋CT相当,仅对贲门胃底部癌判断正确率略低。     

In vitro ultrasound-mediated leakage from phospholipid vesicles

Interest in using ultrasound energy in wound management and intracellular drug delivery has been growing rapidly. Development and treatment optimization of such non-diagnostic applications requires a fundamental understanding of interactions between the acoustic wave and phospholipid membranes, be they cell membranes or liposome bilayers. This work investigates the changes in membrane permeation (leakage mimicking drug release) in vitro during exposure to ultrasound applied in two frequency ranges: “conventional” (1 MHz and 1.6 MHz) therapeutic ultrasound range and low (20 kHz) frequency range. Phospholipids vesicles were used as controllable biological membrane models. The membrane properties were modified by changes in vesicle dimensions and incorporation of poly(ethylene glycol) i.e. PEGylated lipids. Egg phosphatidylcholine vesicles with 5 mol% PEG were prepared with sizes ranging from 100 nm to 1 μm. Leakage was quantified in terms of temporal fluorescence intensity changes observed during carefully controlled ultrasound ON/OFF time intervals. Custom-built transducers operating at frequencies of 1.6 MHz (focused) and 1.0 MHz (unfocused) were used, the I_spta of which were 46.9 W/cm² and 3.0 W/cm², respectively. A commercial 20 kHz, point-source, continuous wave transducer with an I_spta of 0.13 W/cm² was also used for comparative purposes. Whereas complete leakage was obtained for all vesicle sizes at 20 kHz, no leakage was observed for vesicles smaller than 100 nm in diameter at 1.6 or 1.0 MHz. However, introducing leakage at the higher frequencies became feasible when larger (greater than 300 nm) vesicles were used, and the extent of leakage correlated well with vesicle sizes between 100 nm and 1 μm. This observation suggests that physico-chemical membrane properties play a crucial role in ultrasound mediated membrane permeation and that low frequency (tens of kilohertz) ultrasound exposure is more effective in introducing permeability change than the “conventional” (1 MHz) therapeutic one. The experimental data also indicate that the leakage level is controlled by the exposure time. The results of this work might be helpful to optimize acoustic field and membrane parameters for gene or drug delivery. The outcome of this work might also be useful in wound management.     

Coded excitation using biphase-coded pulse with mismatched filters for high-frequency ultrasound imaging

A scheme of using phase-coded excitation and mismatched filter compression for high-frequency ultrasound imaging is presented in this paper. Biphase-coded pulses were constructed to excite the transducer. Received signals were compressed with mismatched filters optimized by minimizing peak-sidelobe-level (PSL). Both simulation and experiments were carried out to demonstrate the advantage of this technique. The simulation results demonstrated a possible sidelobe reduction (<-90 dB) with a slightly decrease of the signal-to-noise ratio of less than 1 dB compared with the compression using matched filters alone. The experimental results showed about 14 dB SNR improvement as well as -40 dB sidelobe level when the Barker-13 code excitation with 3-cycle sinusoidal wave carrier was used.     

Sample preparation methods for subsequent determination of metals and non-metals in crude oil—A review

In this review sample preparation strategies used for crude oil digestion in last ten years are discussed focusing on further metals and non-metals determination. One of the main challenges of proposed methods has been to overcome the difficulty to bring crude oil samples into solution, which should be compatible with analytical techniques used for element determination. On this aspect, this review summarizes the sample preparation methods for metals and non metals determination in crude oil including those based on wet digestion, combustion, emulsification, extraction, sample dilution with organic solvents, among others. Conventional methods related to wet digestion with concentrated acids or combustion are also covered, with special emphasis to closed systems. Trends in sample digestion, such as microwave-assisted digestion using diluted acids combined with high-efficiency decomposition systems are discussed. On the other hand, strategies based on sample dilution in organic solvents and procedures recommended for speciation analysis are reported as well as the use of direct analysis in view of the recent importance for crude oil field. A compilation concerning sample preparation for crude oil provided by official methods as well as certified reference materials available for accuracy evaluation is also presented and discussed.     

Synergistic bactericidal effects and mechanisms of low intensity ultrasound and antibiotics against bacteria: a review

Low intensity ultrasonic therapy is always an important research area of ultrasonic medicine. This review concentrates on low intensity ultrasound enhancing bactericidal action of antibiotics against bacteria in vitro and in vivo, including planktonic bacteria, bacterial biofilms, Chlamydia, and bacteria in implants. These literatures show that low intensity ultrasound alone is not effective in killing bacteria, while the combination of low intensity ultrasound and antibiotics is promising. Low intensity ultrasound facilitating antibiotic treatment is still in its infancy, and still requires a great deal of research in order to develop the technology on medical treatment scale.