fig2

Figure 2. Behavior of microbubbles exposed to ultrasound. Microbubbles oscillate in a symmetrical manner at very low MI (< 0.1) with stable linear scattering. In contrast, asymmetrical oscillations are observed at low/medium MI (0.2-0.6), with microbubbles expanding more than they contract because they are more resistant to compression. This asymmetry causes harmonic emissions. Transient non-linear scattering occurs at high MI (> 0.6), and is followed by microbubble destruction. MI: mechanical index