Improving the heating efficiency of high intensity focused ultrasound ablation through the use of phase change nanodroplets and multifocus sonication

Thermal ablation by ultrasound is being explored as a local therapy for cancers of soft tissue, such as the liver or breast. One challenge for these treatments are off-target effects, including heating outside of the intended region or skin burns. Improvements in heating efficiency can mitigate these undesired outcomes, and here, we describe methods for using phase-shift nanodroplets (PSNDs) with multi-focus sonications to enhance volumetric ablation and ablation efficiency at constant powers while increasing the pre-focal temperature by less than 6 ∘C. Multi-focus ablation with 4 foci performed the best and achieved a mean ablation volume of 120.2 ± 22.4 mm3 and ablation efficiency of 0.04 mm3 J−1 versus an ablation volume of 61.2 ± 21.16 mm3 and ablation efficiency of 0.02 mm3 J−1 in single focus case. The combined use of PSNDs with multi-focal ultrasound presented here is a new approach to increasing ablation efficiency while reducing off-target effects and could be generally applied in various focused ultrasound thermal ablation treatments.