Ablation area measured at the focal target and at the skin. Ablation area was quantified by counting the number of image pixels wherein a temperature rise greater than or equal to 23 °C was measured by MR thermometry following 15 s of HIFU at 15 W. Ablation area was assessed a at the targeted region (acoustic focus) and b at the surface of the animal. The gray solid line indicates the mean ablation area when HIFU was applied without injection of any perfluorocarbon agents (sham control experiments), and the dotted lines indicate one standard deviation. The asterisk indicates significance (p < 0.05) compared to the sham control results. The dagger indicates significance (p < 0.05) between microbubbles and nanodroplets. The data is displayed as mean ± S.D., where n = 3 to 5 (see Table 1).