抄録
Ultrasound has a low enough tissue attenuation coefficient to penetrate intervening tissues and deliver its energy to non-superficial objects, while maintaining the ability to focus the energy into small volumes. This confers a unique advantage over electromagnetic modalities such as laser beams or microwaves when applied to non-invasive and selective treatment of non-superficial tumors. During ultrasonic coagulation treatment, the tissue in the focal zone is heated above the critical temperature at a faster rate than the tissue heat diffusion, resulting in a well-defined coagulation volume similar to the focal spot. However, the small size of the spot leads to a long total treatment time. A split-focus method can multiply the coagulation volume and the throughput of treatment. Cytotoxic effects can be induced ultrasonically by activating specific chemicals by acoustic cavitation. This effect can be used as sonodynamic treatment if cavitation is produced efficiently in a well-controlled manner. Second-harmonic superimposition can reduce the ultrasonic intensity required to produce cavitation by more than one order of magnitude and can produce sonochemically active cavitation with traveling waves without depending on standing waves. A therapeutic system employing both of these new methods of treatment is now being developed.
