28kHz超音波照射下のゼラチンゲルにおける単一ガス気泡の非球形振動

抄録

The viscoelasticity of soft tissue surrounding bubbles play an important role in bubble dynamics in the context of ultrasound applications in medicine. Resonant bubbles oscillating with large amplitude often lose their sphericity in shape; the Rayleigh–Plesset formulation designed for analysis of spherical bubble dynamics will fail in this case. In this study, we experimentally observe the non-spherical oscillation of a gas bubble in gelatin gels, as a tissue phantom, under 28-kHz ultrasound irradiation; we treat the gelatin concentration and the equilibrium bubble radius, and the pressure amplitude of the ultrasound as experimental parameters. A spherical bubble is generated by focusing a laser pulse into a gel that is supersaturated with the dissolved air; the nucleated bubble shows gradual growth due to influx of the dissolved gas, thereby varying its equilibrium radius (from 50 μm to 200 μm). The ultrasound with varying its pressure amplitude is irradiated toward the bubble and the bubble oscillation is recorded with a high-speed camera. The experiments show that an increase of the gelatin gel concentration leads to an increase of the natural frequencies of non-spherical mode oscillations and suppression of their oscillation amplitude.