A high-magnification and high-speed system for the observation of microbubbles under ultrasound exposure

Clinical applications of ultrasound contrast agent (UCA) have been widely studied in recent years, but the behavior of microbubbles exposed to ultrasound is not fully understood yet. The authors developed a high-magnification and high-speed observation system, and they studied the dynamic behavior of cavitation bubbles, air-contained microbubbles, and UCA under ultrasound exposure. The dynamic behavior of cavitation was observed at the frame rate of 2×10⁶ frames/s with magnification of ×15, and periodic expansion and shrinkage due to exposure to ultrasound were observed. The maximum diameter of a bubble was around 10 μm in the expansion phase, and it was too small to observe in the compression phase. Air-contained microbubbles of 20-100 μm in diameter and UCA of 3-5 μm in diameter were also observed at the maximum imaging rate of 1×10⁷ frames/s and maximum magnification of ×100. Typically, microbubbles exposed to ultrasound pressure undergo repeated expansion and shrinkage and reach a critical size, then collapse