In this first part of the review, we will focus on and discuss various aspects of low-intensity ultrasound (US), with emphasis on mild thermal effects, apoptosis induction, and sonomechanical effects. Mild thermal effects of US have been commonly applied to physical therapy. Though US has clear beneficial effects, the advantage of using US over other heating modalities remains unclear. US has also been used in vivo and clinically in the treatment of wounds and fractures, with promising results. On the biomolecular level, studies have shown that US can induce apoptosis and that certain conditions can provide optimal apoptosis induction. As to potential therapeutic applications, in addition to the thermal and other physical effects, apoptosis induction by US may offer direct and rapid treatment of tumors or cancer tissues. Technological advances and rapidly accelerating research in this field are providing an ever-increasing array of therapeutic options for lowintensity US.
Keywords: low-intensity ultrasound; physical therapy; sonomechanical effects.