Influence of Bubble Size Distribution on the Echogenicity of Ultrasound Contrast Agents

Abstract

Gorce J-M, Arditi M, Schneider M. Influence of bubble size distribution on the echogenicity of ultrasound contrast agents: A study of SonoVue™. Invest Radiol 2000;35:661–671. RATIONALE AND OBJECTIVES. To study the relative contributions of different bubble size classes to SonoVue™’s echogenicity in fundamental acoustic imaging modes. SonoVue™ is a contrast agent, previously known as BR1, with a bubble size distribution extending from approximately 0.7 to 10 μm. METHODS. A model for the acoustic response of SonoVue™ was determined and validated for a set of experimental data. This model was used to simulate the acoustic response of a standard batch of SonoVue™ as the sum of responses of nonoverlapping bubble size classes. RESULTS. The simulation was first validated for a standard SonoVue™ bubble size distribution. When this distribution was considered as five size classes with equal numbers of bubbles, it was found that bubbles smaller than 2 μm accounted for 60% of the total number but contained only 5% of the total gas volume. The simulation results indicated marked differences in the acoustic contributions from these classes, with 80% of the acoustic efficacy provided by bubbles 3 to 9 μm in diameter. The study also compared bubble distributions in number, surface, and volume, with the distribution computed in terms of acoustic efficacy. CONCLUSIONS. This study shows why bubble volume is a much better indicator of SonoVue™’s efficacy than is bubble count. A low threshold in diameter was found for SonoVue™ microbubbles at approximately 2 μm, under which size bubbles do not contribute appreciably to the echogenicity at medical ultrasound frequencies.