title: Individual lipid encapsulated microbubble radial oscillations: Effects of fluid viscosity.
abstract: Ultrasound-stimulated microbubble dynamics have been shown to be dependent on intrinsic bubble properties, including size and shell characteristics. The effect of the surrounding environment on microbubble response, however, has been less investigated. In particular, microbubble optimization studies are generally conducted in water/saline, characterized by a 1 cP viscosity, for application in the vasculature (i.e., 4 cP). In this study, ultra-high speed microscopy was employed to investigate fluid viscosity effects on phospholipid encapsulated microbubble oscillations at 1 MHz, using a single, eight-cycle pulse at peak negative pressures of 100 and 250 kPa. Microbubble oscillations were shown to be affected by fluid viscosity in a size- and pressure-dependent manner. In general, the oscillation amplitudes exhibited by microbubbles between 3 and 6 μm in 1 cP fluid were larger than in 4 cP fluid, reaching a maximum of 1.7-fold at 100 kPa for microbubbles 3.8 μm in diameter and 1.35-fold at 250 kPa for microbubbles 4.8 μm in diameter. Simulation results were in broad agreement at 250 kPa, however generally underestimated the effect of fluid viscosity at 100 kPa. This is the first experimental demonstration documenting the effects of surrounding fluid viscosity on microbubble oscillations, resulting in behavior not entirely predicted by current microbubble models.
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Brandon
authors.initials: B
authors.lastname: Helfield
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Xucai
authors.initials: X
authors.lastname: Chen
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Qin
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Flordeliza S
authors.initials: FS
authors.lastname: Villanueva
mesh_terms: D003287:Contrast Media / Q000737:chemistry; D004777:Environment; D045423:Microbubbles; D009038:Motion; D010743:Phospholipids / Q000737:chemistry*; D014465:Ultrasonics; D014783:Viscosity
chemical_list: D003287:Contrast Media; D010743:Phospholipids
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