Transient interactions among ultrasound, microbubbles, and microvessels were studied using high-speed photomicrography. We observed liquid jets, vessel distention (motion outward against the surrounding tissue), and vessel invagination (motion inward toward the lumen). Contrary to current paradigms, liquid jets were directed away from the nearest vessel wall and invagination exceeded distention. These observations provide insight into the mechanics of bubble-vessel interactions, which appear to depend qualitatively upon the mechanical properties of biological tissues.
Comparisons of the spectral characteristics of sonoluminescence from cavitation in bubble fields (MBSL) versus cavitation of single bubbles (SBSL) have been made for aqueous solutions under similar experimental conditions. In particular, alkali metal chloride solutions exhibit sonoluminescence emission from excited state Na or K atoms in MBSL, while SBSL exhibits no such emission. Since the metal ions are not volatile, participation of the initially liquid phase must occur in MBSL. Surface wave and microjet formation in cavitating bubble fields versus the high spherical symmetry of collapse of an isolated bubble may account for the observed differences.PACS numbers: 78.60. Mq, 43.25.+y, 47.40.Nm It has long been known that under certain conditions acoustic irradiation of a liquid can result in light emission, a phenomenon called sonoluminescence (SL) [1,2].The process typically involves the application of high intensity ultrasound to a liquid by an immersed acoustic horn driven with a piezoelectric transducer. The resulting cavitation-bubble field is made up of a complex distribution of gas and vapor-filled bubbles of various equilibrium sizes that pulsate at various phases relative to the driving acoustic pressure field. The bubble dynamics is further complicated by interactions with neighboring bubbles [3] as well as with the vessel walls. Depending on the location within the pressure field and these other infIuences, some of the bubbles may grow dramatically during the negative portion of the sound field, followed by a quasiadiabatic collapse that results in the heating of the bubble interior and the subsequent emission of light [4].In spite of the complexity of cavitating bubble fields, many studies have been made of multibubble sonoluminescence (MBSL) and the influences of fluid and gas properties. The optical spectra of MBSL typically contains distinct, pressure broadened molecular or atomic emission bands. Of particular significance here is the identification of individual transitions from excited states of diatomic carbon (Cq) that contribute to the optical spectrum of MBSL in nonaqueous liquids. The fitting of the measured spectrum of C2 permitted the measurement of an effective rotational and vibrational temperature of the excited states of Cq of 5100 K [5].Recent experimental advances [6] have also made it possible to examine both the temporal and spectral nature of sonoluminescence from a single bubble (SBSL). Here a single bubble is acoustically levitated in an aqueous solution that has been partially degassed. The bubble can be made to undergo large-amplitude, nonlinear, presumably radial pulsations during which light emission can occur. Some properties of SBSLinclude [7] the synchronous emission of light with each and every acoustic cycle, tem-poral flash widths of less than 50 ps, and a continuous spectral energy density that increases from the visible into the UV, with eventual fall off due to UV absorption by the surrounding water. In addition, unlike in MBSL, there are little or no electroni...
Experiments were performed to measure the dynamical response of individual SonoVue microbubbles subjected to pulsed ultrasound. Three commonly used bubble dynamic models (i.e., Hoff's, Sarkar's, and linearized Marmottant's models) were compared to determine the most appropriate model for fitting to the experimental data. The models were evaluated against published optical microscopy data. The comparison suggests that it is difficult to rank these models for lipid-shelled microbubbles undergoing small-amplitude oscillations, because under these conditions the shell parameters in these models are closely related. A linearized version of the Marmottant model was used to estimate the shell parameters (i.e., shear modulus and shear viscosity) of SonoVue microbubbles from the experimental light scattering data, as a function of ambient microbubble radius. The SonoVue microbubble shell elasticity and dilatational viscosity increase with ambient bubble radius, in agreement with previously published data. The results suggest that light scattering, used in conjunction with one of several popular bubble dynamics models, is effective at characterizing microbubble response and evaluating shell parameters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.