“Used for body sculpting, HIFU delivers focused, high intensity ultrasonic energy to deep subcutaneous tissue, producing heat capable of ablating adipose tissue and thermally modifying collagen. It seems intuitive that the rate of heating should be proportional to the intensity and frequency of the ultrasound, with higher frequency and intensity resulting in more rapid heating in the focal zone. In reality, high intensities in the HIFU focal zone result in nonlinear effects in the ultrasonic beam that multiply the already high heating rate several-fold. This results in much shorter treatment times than those calculated using linear intensity levels. Exposure of adipocytes to a temperature of 56°C or higher for 1 s is adequate to cause rapid cell death by coagulative necrosis. For body sculpting, thermal HIFU focuses energy adequate for ablation of targeted adipose tissue using ultrasonic waves at a frequency of 2 MHz and an intensity exceeding 1,000 W/cm2. Findings have identified 2 MHz as the optimal HIFU frequency, which is capable of disrupting adipocytes and contracting collagen fibers to tighten skin. A high degree of focusing allows ultrasonic energy to pass through the skin and intervening tissue layers above the focal zone at an intensity low enough not to cause undue heating in them. The high intensity in the focal zone, enhanced by nonlinear effects, results in a high heating rate and coagulative necrosis if treatment parameters are chosen properly. High intensity in the focal zone also causes nonlinear effects in the ultrasonic beam that enhances the already high heating rate, resulting in much faster treatment times.”
Jewell, M.L.,Solish, N.J., Desilets, C.S. Noninvasive Body Sculpting Technologies with an Emphasis on High-Intensity Focused Ultrasound. Aesth Plast Surg 2011.