The invention relates to an emulsion that can be activated by ultrasounds, comprising, in an emulsion in an aqueous solution, microparticles having a diameter of less than 10 μm and containing an active agent and a gaseous precursor in a liquid form, encapsulated by a first emulsifier. The microparticles contain nanoparticles smaller than 1 μm, in an emulsion in the gaseous precursor, each nanoparticle comprising an inner liquid that contains the active agent and is encapsulated by a second emulsifier.