Objective: Thermal therapies are rapidly gaining importance in oncology as an alternative to radio-therapy and surgery. The possibility to locally deposit thermal energy in a non-invasive way opens a path towards new therapeutic strategies with improved reliability and reduced associated trauma leading to improved efficacy, reduced hospitalisation and costs. Liver and kidney tumors represent a major health problem because not allpatients are suitable for curative treatment with surgery. Currently, radio-frequency is the most used method for percutaneous ablation and the development of a completely non-invasive method based on MR guided high intensity focused ultrasound (HIFU) treatments is of particular interest, since the energy source is located outside the body. This project addressed technological challenges for the treatment of liver and kidney, related to their motion and their location within the thoracic cage.Material and methods: This project proposed safe and non-invasive methods for MR-guided thermal ablation of malignant tumors of liver and kidney with HIFU. Real-time MRI was used to precisely control heat deposition with HIFU within the targeted pathological area despite the motion of these organs, in order to provide an effective treatment with a reduced duration and an increased level of safety for the patient. New technologies were studied for the development of matrix transducers able to generate high acoustic power.Discussion: 3D Real-Time MRI guidance of a HIFU intervention as well as inter-costal firing were realized in vivo in pig liver during breathing under real-time MR thermometry over sustained periods of several minutes. The ability to generate acoustic power as high as up to five time the usual level was demonstrated in vitro thanks to the development of the new transducer technology proposed in this project.Conclusion: A fully MR-integrated HIFU treatment platform dedicated to the treatment of cancer in mobile abdominal organs was developed.< Réduire