Magnetic Resonance guided High Intensity Focused Ultrasound (MRgHIFU) is a promising approach for the non-invasive ablation of localized tumors. Ablation of highly perfused tumors is challenging due to the heat sink effect. We developed a new concept of endovascular liquid core micro-droplets, used as sono-sensitizers for the enhanced absorption of the HIFU beam. We demonstrated the improvement of the HIFU thermal effect after adjunction of sono-activable micro-droplets in the perfusion fluid of freshly excised viable pig kidneys. Temperature maps were computed using the PRFS method to prove the enhancement of thermal contrast.