The action that can be found in HIFU involves thermal as well as cavitation to cause cell disruption and cell death. The ultrasound energy cause molecular vibrations which result in heat generation and a rapid rise in temperature along the focal zone which will then stimulate collagen renewal. On a cellular level, the elevated temperatures also trigger a mechanical process that will result in cell death hence the elimination of fat cells. Meanwhile, Ultherapy relies only on heat to stimulate collagen contraction. 

HIFU triggers two concurrent mechanisms to bring about skin tightening/lifting, while taking care of the stubborn fats to better define facial contours.