Acoustic characterization of monodisperse lipid-coated microbubbles: Relationship between size and shell viscoelastic properties

Abstract

The acoustic attenuation spectrum of lipid-coated microbubble suspensions was measured in order to characterize the linear acoustic behavior of ultrasound contrast agents. For that purpose, microbubbles samples were generated with a very narrow size distribution by using microfluidics techniques. A performance as good as optical characterization techniques of single microbubbles was achieved using this method. Compared to polydispersions (i.e., contrast agents used clinically), monodisperse contrast agents have a narrower attenuation spectrum, which presents a maximum peak at a frequency value corresponding to the average single bubble resonance frequency. The low polydispersity index of the samples made the estimation of the lipid viscoelastic properties more accurate since, as previously reported, the shell linear parameters may change with the equilibrium bubble radius. The results showed the great advantage of dealing with monodisperse populations rather than polydisperse populations for the acoustic characterization of ultrasound contrast agents.

Design of Highly Stable Echogenic Microbubbles through Controlled Assembly of Their Hydrophobin Shell

“…HFBII Gibbs monolayers adsorbed at the air/water interface are known to exhibit ac oncentration-dependent transition from af luid to a2 D solid state,r esulting in high shear elasticity. [10] Finally,s ome feasibility tests showed that dispersing HFBII and preparing microbubbles using standard procedures leads to heterogeneous mixtures consisting largely of micron-sized aggregates along with both spherical and elongated microbubbles (see below), thus impeding the reproducible and effective formation of echogenic microbubbles. Another consequence of HFBII monolayers being in as olid state is that millimetric [8] and micrometric [9] HFBII-stabilized bubbles adopt elongated shapes.D ispersions containing both elongated and spherical microbubbles are suboptimal as USCAs ince microbubble resonance frequency depends on the radius.…”

“…Another consequence of HFBII monolayers being in as olid state is that millimetric [8] and micrometric [9] HFBII-stabilized bubbles adopt elongated shapes.D ispersions containing both elongated and spherical microbubbles are suboptimal as USCAs ince microbubble resonance frequency depends on the radius. [10] Finally,s ome feasibility tests showed that dispersing HFBII and preparing microbubbles using standard procedures leads to heterogeneous mixtures consisting largely of micron-sized aggregates along with both spherical and elongated microbubbles (see below), thus impeding the reproducible and effective formation of echogenic microbubbles.…”

Pressure dependence of the attenuation and sound speed in a bubbly medium: Theory and experiment

“…To experimentally explore the pressure-dependent changes of the sound speed and attenuation for coated MBs, monodisperse lipid shell MBs were produced using flow-focusing in a microfluidic device as previously described [29,37]. Figure 2 shows the size distribution of the MBs in our experiments.…”

“…Figure 2 shows the size distribution of the MBs in our experiments. The setup for the attenuation and sound speed measurements is the same as the one used in [37]. The thermal properties for the gas can be found in [38].…”

Monodisperse bubbles and droplets for medical applications

“…Clinical ultrasound scanners operate at a narrow frequency bandwidth and as the resonance frequency of a bubble is directly related to its size 37 , only a small fraction of the UCA population resonates to the driving ultrasound field. The sensitivity increase that may result from the use of monodisperse UCA was already frequently suggested 4,64,65,118,[135][136][137] . In-vitro experiments have shown that the echo response of monodisperse bubbles presents a higher inter-echo correlation than that of a polydisperse population 4 .…”