Combined optical sizing and acoustical characterization of single freely-floating microbubbles

Abstract

In this study we present a combined optical sizing and acoustical characterization technique for the study of the dynamics of single freely-floating ultrasound contrast agent microbubbles exposed to long burst ultrasound excitations up to the milliseconds range. A co-axial flow device was used to position individual microbubbles on a streamline within the confocal region of three ultrasound transducers and a high-resolution microscope objective. Bright-field images of microbubbles passing through the confocal region were captured using a high-speed camera synchronized to the acoustical data acquisition to assess the microbubble response to a 1-MHz ultrasound burst. Nonlinear bubble vibrations were identified at a driving pressure as low as 50 kPa. The results demonstrate good agreement with numerical simulations based on the shell-buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499–3505 (2005)]. The system demonstrates the potential for a high-throughput in vitro characterization of individual microbubbles.

Time-resolved absolute radius estimation of vibrating contrast microbubbles using an acoustical camera

“…Another potential use of the system is to assess the range and cause of differences in acoustic responses of MBs with comparable sizes. Considerable differences in response have been reported for polydisperse MBs with marginal size differences (Luan et al, 2016). It would be particularly interesting to investigate this aspect for monodisperse MB because their formation process is more stringently controlled.…”

“…Typically, MBs are characterized using bulk measurements, which effectively integrates all individual bubble responses into one (Alsadiq et al, 2021;Segers et al, 2016;Segers et al, 2018). However, it is known that MBs of the same size can exhibit significantly different acoustic responses-even when derived from the same bubble populationbecause of differences in shell properties (Luan et al, 2016;Sijl et al, 2011). To assist research on improved MB formulations and contrast imaging techniques, we investigate the vibrational behavior of individual MBs under different driving conditions.…”

“…The resonance of coated MBs, however, depends on coating composition (Marmottant et al, 2005;Sirsi and Borden, 2009), which invalidates the method. Adding single-shot optics capabilities to an AC is possible (Luan et al, 2016) but complicates the setup and measurements considerably, requiring precise alignment of the optical and acoustical foci.…”