Volume 116, Issue 4, October 2004
Index of content:
- BIOACOUSTICS 
116(2004); http://dx.doi.org/10.1121/1.1777855View Description Hide Description
This article reports the effect of surface agitation of culture medium on ultrasound-mediated gene transfection in vitro and its possible mechanisms. The possibility of active induction of bubbles without using contrast microbubbles for effective gene transfer was also demonstrated. Cultured HeLa cells mixed with green fluorescent protein plasmid were exposed to 1.0 MHz ultrasound in 24-well culture plates. Up to 26% transfection efficiency in the survival cell population was achieved in samples exposed to 0.44 MPa ultrasound pulses with the presence of surface agitation. Inertial cavitation and bubble generation were observed throughout the ultrasound exposure. When surface agitation was suppressed by covering the medium surface with a thin membrane, bubble generation and gene transfection were significantly suppressed. Interestingly, transfection efficiency could be partially resumed by adding a small amount of culture medium onto the covering membrane to rebuild the surface agitation and bubble generation.Pressure fluctuation and transient high-pressure loci were found in samples with surface agitation. Numerical simulations of bubble dynamics showed that transient high pressures above the inertial cavitation threshold could generate bubbles, which might be subsequently stabilized at lower pressures by rectified diffusion, and exert strong shear forces that might create transient pores on cell membranes to facilitate gene transfer.
Experimental validation of a tractable numerical model for focused ultrasound heating in flow-through tissue phantoms116(2004); http://dx.doi.org/10.1121/1.1787124View Description Hide Description
Heating from high intensity focused ultrasound (HIFU) can be used to control bleeding, both from individual blood vessels as well as from gross damage to the capillary bed. The presence of vascularity can limit one’s ability to elevate the temperature owing to convective heat transport. In an effort to better understand the heating process in tissues with vascular structure we have developed a numerical simulation that couples models for ultrasound propagation, acoustic streaming,ultrasound heating and blood cooling in a Newtonian viscous medium. The 3-D simulation allows for the study of complicated biological structures and insonation geometries. We have also undertaken a series of in vitroexperiments employing non-uniform flow-through tissue phantoms and designed to provide verification of the model predictions. We show that blood flow of 2 cm/s (6.4 ml/min through a 2.6 mm ‘vessel’) can reduce peak temperature in a vessel wall by 25%. We also show that HIFU intensities of can induce acoustic streaming with peak velocities up to 5 cm/s and this can reduce heating near a vessel wall by more than 10%. These results demonstrate that convective cooling is important in HIFU and can be accounted for within simulation models.
Geographic variation and acoustic structure of the underwater vocalization of harbor seal (Phoca vitulina) in Norway, Sweden and Scotland116(2004); http://dx.doi.org/10.1121/1.1782933View Description Hide Description
The male harbor seal (Phoca vitulina) produces broadband nonharmonic vocalizations underwater during the breeding season. In total, 120 vocalizations from six colonies were analyzed to provide a description of the acoustic structure and for the presence of geographic variation. The complex harbor seal vocalizations may be described by how the frequency bandwidth varies over time. An algorithm that identifies the boundaries between noise and signal from digital spectrograms was developed in order to extract a frequency bandwidth contour. The contours were used as inputs for multivariate analysis. The vocalizations’ sound types (e.g., pulsed sound, whistle, and broadband nonharmonic sound) were determined by comparing the vocalizations’ spectrographic representations with sound waves produced by known sound sources. Comparison between colonies revealed differences in the frequency contours, as well as some geographical variation in use of sound types. The vocal differences may reflect a limited exchange of individuals between the six colonies due to long distances and strong site fidelity. Geographically different vocal repertoires have potential for identifying discrete breeding colonies of harbor seals, but more information is needed on the nature and extent of early movements of young, the degree of learning, and the stability of the vocal repertoire. A characteristic feature of many vocalizations in this study was the presence of tonal-like introductory phrases that fit into the categories pulsed sound and whistles. The functions of these phrases are unknown but may be important in distance perception and localization of the sound source. The potential behavioral consequences of the observed variability may be indicative of adaptations to different environmental properties influencing determination of distance and direction and plausible different male mating tactics.