The Effects of Nonfocused External Ultrasound on Tissue Temperature and Adipocyte Morphology

Background: Nonfocused externally applied ultrasound energy has been used extensively in the clinical setting for noninvasive body contouring on the premise that ultrasonic diathermy may have a reducing effect on adipose tissue. Objectives: The authors document both the time/temperature relationships and cellular changes following nonfocused and weakly focused ultrasound treatments in an animal model. Methods: Nonfocused ultrasound treatments were administered to 3 Yorkshire pigs, at clinically recommended settings, for two 12-minute intervals. Tissue temperatures were recorded. Lymph fluid samples were taken pretreatment from the control side and posttreatment from the treated side. Biopsies were taken of the skin, adipose tissue, muscle, and lymph nodes on both the control side (pretreatment) and the ultrasound-treated side (posttreatment) for histological examination. Results: Lymph fluid analysis revealed highly elevated triglyceride values on the treated side versus the control. Analysis of lymph node biopsies revealed free vacuoles of fat within the lymph node tissue on the treated side compared with normal controls. In situ temperature measurements indicated that the device produced uniform heating throughout the adipose tissue layer. Electron microscopy of the treated adipose tissue revealed alterations in the cellular architecture without necrosis and free lipids within the extracellular space. Conclusions: On the basis of the increase of free lipids in the lymph system posttreatment, the increase in free lipids within the lymph nodes on the treated side, and the free lipids in the extracellular space without cell necrosis, we conclude that treatment with this device reduces adipose tissue by altering the permeability of the adipocytes.