Fluid Viscosity Affects the Fragmentation and Inertial Cavitation Threshold of Lipid-Encapsulated Microbubbles

Ultrasound Med Biol. 2016 Mar;42(3):782-94. doi: 10.1016/j.ultrasmedbio.2015.10.023. Epub 2015 Dec 7.

Abstract

Ultrasound and microbubble optimization studies for therapeutic applications are often conducted in water/saline, with a fluid viscosity of 1 cP. In an in vivo context, microbubbles are situated in blood, a more viscous fluid (∼4 cP). In this study, ultrahigh-speed microscopy and passive cavitation approaches were employed to investigate the effect of fluid viscosity on microbubble behavior at 1 MHz subject to high pressures (0.25-2 MPa). The propensity for individual microbubble (n = 220) fragmentation was found to significantly decrease in 4-cP fluid compared with 1-cP fluid, despite achieving similar maximum radial excursions. Microbubble populations diluted in 4-cP fluid exhibited decreased wideband emissions (up to 10.2 times), and increasingly distinct harmonic emission peaks (e.g., ultraharmonic) with increasing pressure, compared with those in 1-cP fluid. These results suggest that in vitro studies should consider an evaluation using physiologic viscosity perfusate before transitioning to in vivo evaluations.

Keywords: Fluid viscosity; Fragmentation; High-speed imaging; Inertial cavitation; Microbubbles; Stable cavitation; Ultrasound.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Capsules / chemistry*
  • Capsules / radiation effects
  • Contrast Media / chemistry
  • Contrast Media / radiation effects
  • Gases / chemical synthesis*
  • High-Energy Shock Waves
  • Lipids / chemistry*
  • Lipids / radiation effects
  • Materials Testing
  • Microbubbles*
  • Radiation Dosage
  • Rheology / methods
  • Solutions / chemistry
  • Solutions / radiation effects
  • Sonication / methods*
  • Viscosity

Substances

  • Capsules
  • Contrast Media
  • Gases
  • Lipids
  • Solutions