Figure 3: Behavior of microbubbles depends on the amplitude of ultrasound to which they are exposed. At very low acoustic power (mechanical index <0.05–0.1), microbubble oscillates in relatively symmetrical backscattering at the same frequency of incident ultrasound. At a slightly higher mechanical index of 0.1–0.3, the microbubble becomes somewhat oscillates in a nonlinear manner (nonlinear response), backscattering a variety of frequencies (harmonic). Higher acoustic pressures ( M I > 0 . 3 –0.6) destroy the microbubbles with high-intensity backscatter response.