BACKGROUND

High-intensity focused ultrasound (HIFU) was first used in research applications in 1942. Fry treated human subjects in 1958. It has since moved from being a research tool to an accepted part of the clinician's armamentarium. HIFU has been used clinically for many years to treat a variety of lesions in the liver, bladder, kidneys, prostate, breast, testes, uterus, and vasculature. Currently, several commercially available HIFU devices are available for these purposes. This chapter will address the next generation of HIFU devices for body sculpting, developed by LipoSonix Inc.

MECHANISMS OF ACTION OF HIFU

HIFU acts on tissue through two main mechanisms: thermal and thermomechanical effects. HIFU can reliably and predictably raise the temperature of the tissue in the focal zone to greater than 56 degrees Celsius to cause thermal toxicity. Shear forces, generated by the pressure wave and cavitation, can cause cellular disruption, but typically only in the focal area. It should be noted that because of the physics of HIFU technology, the mechanical effects will always be associated with temperature increases in tissue.

A unique property of HIFU, unlike other therapeutic energy modalities, is that the HIFU energy can be accurately controlled, including the depth of treatment. Numerous authors have shown that precise lesions can be reliably produced only in targeted locations, while the surrounding tissue outside of the HIFU focal zone is not affected. This is consistent with our research with the LipoSonix prototype.