The present invention relates to ultrasound (US) mediated delivery of therapeutic agents, such as the delivery of a drug, gene, nanoparticle or radioisotope, using a bi-phasic microparticle system comprising gas microbubbles, emulsion microdroplets and clusters thereof. Thus, the present invention relates to a cluster composition and a pharmaceutical composition, and their use for delivery of therapeutic agents and as a contrast agent for ultrasound imaging. It further relates to methods for delivering such therapeutic agents and to the use of said compositions.
