Ultrasound attenuation in encapsulated microbubble suspensions: The multiple scattering effects

Area of Science:

• Ultrasound imaging
• Acoustic scattering
• Microbubble dynamics

Background:

• Previous studies observed image distortions from microbubble multiple scattering (MS) in ultrasound imaging.
• The precise mechanism driving these MS effects in encapsulated microbubbles remains incompletely understood.

Purpose of the Study:

• To investigate and quantify the multiple scattering (MS) effects of encapsulated microbubbles in contrast imaging.
• To analyze the relationship between MS effects and physical properties like bubble concentration, size, and shell thickness.
• To discuss the implications of MS effects in current ultrasound imaging practices.

Main Methods:

• Modified the effective medium approach (including high-order rescattering) and the lowest-order approximation approach (ignoring higher-order rescattering) to model encapsulated microbubble suspensions.
• Defined discrepancies in calculated attenuation coefficients between the two approaches as a measure of MS effects.
• Simulated intrinsic relations between MS effects and microbubble physical properties.

Main Results:

• MS effects become significant in suspensions of identical microbubbles (>12 microm) when concentrations exceed 1 x 10(5) bubbles/mL.
• Simulations examined MS effects in microbubbles with broad size distributions, referencing prior experimental data.
• Calculated scattering and extinction cross-sections for individual microbubbles to further investigate MS mechanisms.

Conclusions:

• The study provides a quantitative measure for MS effects in microbubble suspensions.
• Identified critical thresholds for bubble concentration and size where MS effects become prominent.
• Offers insights into the mechanisms of MS effects for ultrasound contrast agents (UCAs).