Non-linear Acoustic Characterization of Microbubbles and Nanobubbles

Abstract

Non-linear contrast-enhanced ultrasound can provide high contrast images by enhancing the non-linear signals from bubble oscillations. In this work, we developed a methodology to detect individual bubble scattering using focused transducers with dilute bubble solutions. Microbubbles and nanobubbles were made with five different lipid shell compositions. Their structure is altered through additional components added to the shell that affect their stability. Dilute samples of bubbles were sonicated at 25 MHz with 30 cycles using a commercial high frequency ultrasound instrument with a pressure range of 75 kPa to 3 MPa. Criteria were developed to ensure signals were only classified if they contained an isolated bubbles’ response. The response of the bubbles of different shell compositions were compared using analysis tools developed. There were no observable differences in the non-linear behaviour between the different shells. However, when comparing microbubbles to nanobubbles differences involving signal count, stability and harmonic amplitudes were observed.