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On the oscillations of microbubbles in tubes with diameters as small as 12 microns

In recent years, experiments coupled with mathematical models have been used to predict microbubble oscillation. Theoretical investigations of ultrasonically driven microbubble behavior are based on the Rayleigh-Plesset equation and assume that the oscillating microbubble is symmetric and in an infinite fluid. The present study shows that constrained microbubble activity in a tube with a diameter on the same order of magnitude as the microbubble diameter differs from previous investigations that assume an infinite fluid. In the microvessel phantoms used in our study, microbubbles expand less in vessels with a diameter of 12 μm than in vessel phantoms with a diameter of 195 μm, with expansion in a 25-μm vessel shown to lie between that observed in the larger and smaller vessels. In the interest of exploring ultrasonic parameters that are relevant to current drug and gene delivery studies, experiments for relative expansion involve a transmission center frequency of 1 MHz with a peak negative pressure (PNP) of 1.4 MPa. Radiation force is also demonstrated following transmission with a center frequency of 5 MHz. Keywords-contrast ultrasound; microbubble; drug delivery; gene therapy