Relationship of Energy Settings and Impedance in Different Anatomic Areas Using a Radiofrequency Device

BACKGROUND: Radiofrequency (RF) used for volumetric heating into the deep dermis has been used effectively for rejuvenation of the face. The delivery of the RF energy depends on several variables, including the electrical impedance of the underlying tissue. OBJECTIVE: To describe the effects of impedance on energy delivery into the treated site. MATERIALS AND METHODS: We report four patients who underwent treatment using the ThermaCool TC system (Thermage, Inc, Hayward, CA, USA). Five sites on each patient were selected for impedance evaluation at two treatment levels. RESULTS: Impedance levels varied only slightly between treatment levels. The impedance levels varied greatly between patients and from site to site in each patient. The impedance levels for each of the patients were greatest on the arm, followed by the forehead, cheeks, and back. CONCLUSION: Energy delivery to a treated area is directly related to the impedance of the tissue. The impedance is shown to vary by site and can be changed by manipulation of the tissue, such as by injection of local anesthesia. Alteration of the impedance may have an effect on the uniform delivery of the selected energy.