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

• Published in: Ultrasound in medicine & biology Vol. 42; no. 3; pp. 782 - 794
• Main Authors: Helfield, Brandon, Black, John J., Qin, Bin, Pacella, John, Chen, Xucai, Villanueva, Flordeliza S.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.03.2016
• Subjects: Capsules - chemistry; Capsules - radiation effects; Contrast Media - chemistry; Contrast Media - radiation effects; Fluid viscosity; Fragmentation; Gases - chemical synthesis; High-Energy Shock Waves; High-speed imaging; Inertial cavitation; Lipids - chemistry; Lipids - radiation effects; Materials Testing; Microbubbles; Radiation Dosage; Radiology; Rheology - methods; Solutions - chemistry; Solutions - radiation effects; Sonication - methods; Stable cavitation; Ultrasound; Viscosity; Stable cavitation; Fluid viscosity; High-speed imaging; Microbubbles; Ultrasound; Inertial cavitation; Fragmentation
• ISSN: 0301-5629; 1879-291X; 1879-291X
• DOI: 10.1016/j.ultrasmedbio.2015.10.023

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.