Ultrasounds are acoustic vibrations with a frequency greater than human hearing (20,000 Hz), issued by transducers able to turn them into "mechanical energy". Applying these transducers on the areas to be treated, it causes the penetration of ultrasounds in the tissue concerned, depending on the frequency of emission (which varies from 1 to 3 MHz) can be obtained several beneficial effects. The main ones are a reactive vasodilation, due to termic effect, and one by mechanical disruption of collagen in tissues. Both are particularly useful in the treatment of localized fat reduction, or other special treatments according to the type of applicator.