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Possible mechanisms of SDT. Ultrasound irradiation induces cavitation around the surface of cancer cells. The energy provided by the collapse of cavitating bubbles initiates the formation of sonoluminescent light in cancer cells. Thus, sonosensitizer is activated from its ground state into an excited state. As the activated sonosensitizer returns to the ground state, the released energy can be transferred to the circumambient oxygen to produce a large amount of ROS including oxygen ion, peroxide and singlet oxygen, which subsequently mediate the mitochondrial-dependent cell apoptosis through the damage of mitochondria membrane and the release of Cyt c.