新型造影剂在结肠超声检查中的应用价值

介绍了一种用于结肠声学检查的新型造影剂，用中草药和食用物质配制而成。对30例经纤维结肠镜或X光钡灌肠确诊的患者，进行了临床应用观察，结果表明，它易于在结肠腔内保留，使结肠壁构成层次清晰的反射界面，从而提高了结肠声学诊断的价值。     

微泡超声造影剂材料研究进展

超声造影剂(UCA)是一类能够显著增强医学超声检测信号的诊断药剂,UCA的出现,开创了无创超声医学的一个新领域.本文对目前应用于微泡超声造影剂的各种材料进行了评述,并按膜材料的不同,从制备角度出发介绍了一些最新的造影剂,介绍了微泡超声造影剂目前在靶向制剂领域的融合,文中还介绍了我们开展的一些工作.     

超声造影剂的非线性参量研究

近年来对超声造影剂的研究兴趣日趋增加是由于它有可能改进超声临床诊断的效果，含有微气泡的液体可用和有效的超声造影剂，液体中气泡的存在提高液体的非线性参量值，本文用检测二次谐波的方法实验上测定了５种超声造影剂的非线性参量，四种含气泡的液体（声振后）和半乳糖Ｅｃｈｏｖｉｓｔ３００。结果表明，含有微气泡的液体具有非常大的非线性参量值，对这种高非线性值的现象文中进行了可能的解释和讨论。     

超声造影剂的强非线性声学特性

含气泡的水具有非常强的非线性声学特性。而超声造影剂则能在流体介质比如血液中产生大量的悬浮气泡。这种气泡在时域是非稳态的。它在强的超声波的驱动下会产生振动，当驱动的频率和强度适当时，会形成共振，从而表现出非常强的非线性。这种自由气泡的共振又会产生声波，从而使声场表现为非线性。本文从理论上分析了这种介质的非线性声学特性，并将超声造影剂注入水中，使其产生相当数量的悬浮自由气泡，以造成这样一种含气泡的流体介质的声学环境，进行超声驱动。从所含气泡的粒度、数量以及声场的非线性特性等方面进行了分析对比，结果表…     

超声造影剂SDA的巨非线性参量

1　引　言近年来 ,含微气泡液体的非线性声学特性引起了人们极大的兴趣。液体中的空气泡是很好的声散射体 ,能产生强的超声散射信号。液体中气泡的非线性振动 ,尤其是在它们的共振频率附近的非线性振动 ,使得它们的存在能够增强液体的声学非线性效应。因此 ,研究含有微气泡的液体的非线性声学特性是非线性声学领域也是它的应用领域的一个重要课题。例如 ,利用含微气泡液体的非线性声特性是水声学中用来增强声参量阵效率的一个有效方法。媒质的非线性声特性可以用非线性声参量 B/A来描述。到目前为止的所有文献上 ,液体、生物流体和组织的非…     

超声微泡造影剂的低频动力学行为

低频超声联合微泡造影剂有可能用于治疗肿瘤,因此开展造影剂低频的动力学特性研究是十分重要的。将低频声场(26.2kHz)中有壳和无壳的微泡造影剂视为以流体为负载的非线性振子,由带耗散函数的拉格朗日方程导出在不可压缩的粘滞流体中造影剂球对称振动的运动方程,利用球谐振腔和Mie散射技术对CO2微泡和带人白蛋白壳的全氟丙烷造影剂微泡进行了气泡散射光强I(t)曲线的实验测定,结果与数值模拟曲线相一致。表明:有壳和无壳的造影剂微泡在低频稳态空化时同样呈现大幅膨胀、迅速塌缩和回弹的非线性振荡;如处于内径较小的微血管中,微泡周期性大幅度(>血管内径)膨胀收缩将会引起血管轴向破裂,形成微血管栓塞;而在塌缩相,微泡内的气体被急剧压缩,泡内压强急剧增大,易在泡壁不稳定处形成高速微射流,诱发内皮细胞损伤而形成血栓。     

超声造影剂衰减系数随时间变化特性研究

为了研究微泡型超声造影剂对声传播衰减的影响,基于气泡动力学理论模型计算微观粒径变化引起的声传播衰减,推导出超声造影剂衰减系数随时间变化的解析表达式,并构建了实验系统,对超声造影剂的衰减系数进行测量。实验结果验证了理论模型的有效性,以及超声造影剂衰减系数随时间变化呈现出指数衰减规律。该研究为减小超声波的传播衰减和畸变提供了依据,使得超声造影剂有效地应用于超声医学领域。     

E1 超声造影剂的非线性参量研究

近年来对超声造影剂的研究兴趣日趋增加是由于它有可能改进超声临床诊断的效果。含有微气泡的液体可用作有效的超声造影剂。液体中气泡的存在可提高液体的非线性参量值。本文用检测二次谐波的方法实验上测定了５种超声造影剂的非线性参量：四种含气泡的液体（声振后）和半乳糖Ｅｃｈｏｖｉｓｔ３００。结果表明，含有微气泡的液体具有非常大的非线性参量值。对这种高非线性值的现象文中进行了可能的解释和讨论     

超声造影剂微泡尺寸分布及浓度测量方法

通过计算机采集光学显微图片,以Image-ProPlus和Photoshop两种图像分析软件实现了微泡的浓度及尺寸分析进行定性测定。结果表明,本文采用的方法快速、简便、重现性良好,可作为超声造影剂微泡的定性测定。     

Mechanisms of contrast agent destruction

Various applications of contrast-assisted ultrasound, including blood vessel detection, perfusion estimation, and drug delivery, require controlled destruction of contrast agent microbubbles. The lifetime of a bubble depends on properties of the bubble shell, the gas core, and the acoustic waveform impinging on the bubble. Three mechanisms of microbubble destruction are considered: fragmentation, acoustically driven diffusion, and static diffusion. Fragmentation is responsible for rapid destruction of contrast agents on a time scale of microseconds. The primary characteristics of fragmentation are a very large expansion and subsequent contraction, resulting in instability of the bubble. Optical studies using a novel pulsed-laser optical system show the expansion and contraction of ultrasound contrast agent microbubbles with the ratio of maximum diameter to minimum diameter greater than 10. Fragmentation is dependent on the transmission pressure, occurring in over 55% of bubbles insonified with a peak negative transmission pressure of 2.4 MPa and in less than 10% of bubbles insonified with a peak negative transmission pressure of 0.8 MPa. The echo received from a bubble decorrelates significantly within two pulses when the bubble is fragmented, creating an opportunity for rapid detection of bubbles via a decorrelation-based analysis. Preliminary findings with a mouse tumor model verify the occurrence of fragmentation in vivo. A much slower mechanism of bubble destruction is diffusion, which is driven by both a concentration gradient between the concentration of gas in the bubble compared with the concentration of gas in the liquid, as well as convective effects of motion of the gas-liquid interface. The rate of diffusion increases during insonation, because of acoustically driven diffusion, producing changes in diameter on the time scale of the acoustic pulse length, thus, on the order of microseconds. Gas bubbles diffuse while they are not being insonified, termed static diffusion. An air bubble with initial diameter of 2 microns in water at 37 degrees C is predicted to fully dissolve within 25 ms. Clinical ultrasound contrast agents are often designed with a high molecular weight core in an attempt to decrease the diffusion rate. C3F8 and C4F10 gas bubbles of the same size are predicted to fully dissolve within 400 ms and 4000 ms, respectively. Optical experiments involving gas diffusion of a contrast agent support the theoretical predictions; however, shelled agents diffuse at a much slower rate without insonation, on the order of minutes to hours. Shell properties play a significant role in the rate of static diffusion by blocking the gas-liquid interface and decreasing the transport of gas into the surrounding liquid. Static diffusion decreases the diameter of albumin-shelled agents to a greater extent than lipid-shelled agents after insonation.     

SURF imaging for contrast agent detection

A contrast agent detection method is presented that potentially can improve the diagnostic significance of ultrasound contrast agents. Second order ultrasound field (SURF) contrast imaging is achieved by processing the received signals from transmitted dual frequency band pulse complexes with overlapping high-frequency (HF) and low-frequency (LF) pulses. The transmitted HF pulses are used for image reconstruction, whereas the transmitted LF pulses are used to manipulate the scattering properties of the contrast agent. In the present paper, we discuss how SURF contrast imaging potentially can overcome problems and limitations encountered with available contrast agent detection methods, and we give a few initial examples of in vitro measurements. With SURF contrast imaging, the resonant properties of the contrast agent may be decoupled from the HF imaging pulses. This technique is thus especially interesting for imaging contrast bubbles above their resonance frequency. However, to obtain adequate specificity, it is typically necessary to estimate and correct for accumulative nonlinear effects in the forward wave propagation.     

Ultrasound-induced gas release from contrast agent microbubbles

We investigated gas release from two hardshelled ultrasound contrast agents by subjecting them to high-mechanical index (MI) ultrasound and simultaneously capturing high-speed photographs. At an insonifying frequency of 1.7 MHz, a larger percentage of contrast bubbles is seen to crack than at 0.5 MHz. Most of the released gas bubbles have equilibrium diameters between 1.25 and 1.75 microm. Their disappearance was observed optically. Free gas bubbles have equilibrium diameters smaller than the bubbles from which they have been released. Coalescence may account for the long dissolution times acoustically observed and published in previous studies. After sonic cracking, the cracked bubbles stay acoustically active.     

Diagnostic ultrasound-induced membrane damage in phagocytic cells loaded with contrast agent and its relation to Doppler-mode images

Cell membrane damage induced by diagnostic ultrasound exposure with contrast agent was examined and related to the display of stimulated acoustical emission in Doppler images. Monolayers of mouse macrophage-like cells were cultured on the inside of one window of an exposure chamber. The monolayers were incubated with 5% Optison/sup /spl reg// (Mallinckrodt, Inc., St. Louis, MO) for 15 minutes then rinsed to remove unattached gas bodies. A Spectra Plus scanner (Diasonics GE Medical Systems, Inc., Cincinnati, OH) in B-scan or Doppler-imaging modes exposed the chamber 3.5 cm away in a 37/spl deg/C water bath. The cells were scored either for uptake of fluorescent Dextran (sonoporation), or for trypan blue dye exclusion (cell death). No significant effect was seen for exposure in any mode without a contrast agent. Significant effects with contrast agent included 5.8% (2.3% standard deviation, SD) fluorescent cells and 33.4% (7.7% SD) trypan blue-stained cells in Doppler-imaging modes, compared to 0.0% and 2.2% (1.7% SD), respectively, in sham exposures. Frames of the power Doppler image were analyzed for pixel brightness to quantify the brief flash in the Doppler window. Although both membrane damage and the flash brightness increased with increasing pressure amplitude, there did not appear to be a direct correlation between the two phenomena.     

Review of shell models for contrast agent microbubbles

Micrometer-scale encapsulated gas bubbles, known as ultrasound contrast agents, are used in ultrasound medical diagnostics for enhancing blood-tissue contrast during an ultrasonic examination. They are also employed in therapy as an activator of drug incorporation or extravasation. Adequate modeling of the effect of encapsulation is of primary importance because it is the encapsulating shell that determines many of the functional properties of contrast agents. In this review, existing approaches to the modeling of the radial motion of an encapsulated bubble are discussed and comparative analysis of available shell models is conducted. The capabilities of the shell models are evaluated in the context of recent experimental observations, such as compression-only behavior and the dependence of shell material properties on initial bubble radius. It is shown that for early shell models, the main problem is that the behavior of encapsulation is described by linear elastic and viscous laws, whereas recent experimental data attest to complicated rheological properties inherent in shell materials. Currently, a trend toward models involving nonlinear laws for shell elasticity and viscosity is observed. In particular, nonlinear models have been proposed that allow one to reproduce compression-only behavior. However, the problem of the radius dependence of shell material parameters remains unsolved.     

Harmonic chirp imaging method for ultrasound contrast agent

Coded excitation is currently used in medical ultrasound to increase signal-to-noise ratio (SNR) and penetration depth. We propose a chirp excitation method for contrast agents using the second harmonic component of the response. This method is based on a compression filter that selectively compresses and extracts the second harmonic component from the received echo signal. Simulations have shown a clear increase in response for chirp excitation over pulse excitation with the same peak amplitude. This was confirmed by two-dimensional (2-D) optical observations of bubble response with a fast framing camera. To evaluate the harmonic compression method, we applied it to simulated bubble echoes, to measured propagation harmonics, and to B-mode scans of a flow phantom and compared it to regular pulse excitation imaging. An increase of approximately 10 dB in SNR was found for chirp excitation. The compression method was found to perform well in terms of resolution. Axial resolution was in all cases within 10% of the axial resolution from pulse excitation. Range side-lobe levels were 30 dB below the main lobe for the simulated bubble echoes and measured propagation harmonics. However, side-lobes were visible in the B-mode contrast images.     

Stable and transient subharmonic emissions from isolated contrast agent microbubbles

Ultrasound contrast agents (UCAs) have been widely studied in recent years in order to improve and develop new, sophisticated imaging techniques for clinical applications. In order to improve the understanding of microbubble-ultrasound interactions, an acoustic dynamic characterization of UCA microbubble behavior was performed in this work using a high frame-rate acquiring and processing system. This equipment is connected to a commercial scanner that provides RF beam-formed data with a frame-rate of 30 Hz. Acquired RF sequences allows us to follow the dynamics of cavitation mechanisms in its temporal evolution during different insonifying conditions. The experimental setup allowed us to keep the bubbles free in a spatial region of the supporting medium, thus avoiding boundary effects that can alter the ultrasound field and the scattered echo from bubbles. The work focuses on the study of subharmonic emission from an isolated bubble of contrast agent. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the stand still of the subharmonic emission, was detected at 3.3 MHz and 5 MHz excitation frequencies. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. An experimental procedure was devised in order to investigate these behaviors and several sequences of RF echo signals and the related spectra, acquired from an isolated bubble in different insonation conditions, are presented and discussed in this paper.