Photothermal therapy is a targeted, non-invasive thermal treatment of cancer. Up to 40 o C temperature increase is obtained in a small volume of malignant cells by using appropriate photoabsorbers and irradiating the tissue with a continuous wave laser. However, in order to ensure successful outcome of photothermal therapy, the tumor needs to be imaged before therapy, the temperature needs to be monitored during therapy and, finally, the tumor needs to be evaluated for necrosis during and after

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... therapy. We investigated the feasibility of ultrasound imaging to track temperature changes during photothermal therapy and elasticity imaging to monitor tumor necrosis after treatment. The image-guided therapy was demonstrated on tissue mimicking phantoms and ex-vivo animal tissue with gold nanoparticles as photoabsorbers. Ultrasound-based thermal imaging effectively generates temperature maps during therapy while elasticity imaging monitors changes in the mechanical properties of tissue before and after therapy, allowing evaluation of treatment efficacy. Results of our study suggest that ultrasound can be used to guide photothermal therapy.