INTRODUCTION
Radiofrequency devices are concurrently similar and different from their laser and light-based counterparts. At the most basic level, similarly to lasers, RF devices work by heating the skin in a controlled and targeted manner. The difference lies in the mechanism by which the skin is heated. RF devices introduce an electric current rather than a light source to deliver energy. One major advantage to this mechanism is that the electrical current is turned into thermal energy at the level of the dermis or subcutis, lessening the complications frequently associated with heating and damage to the epidermis. In addition, RF based devices do not lose energy to diffraction, absorption, and scatter as do light and laser devices.1,2 These RF advantages have helped pique the interest of device manufacturers and treating physicians. In this review, we will discuss the history and evolution of RF technology and a broad range of applications of interest to the cosmetic dermatologist.
History of RF in Medicine
Physicians originally used Radiofrequency in the 1920s for electrocoagulation. Since then it has been used to heat and ablate tissue, including endovenous treatment of incompetent vein,3 joint capsular tightening,4ablation of hepatocellular,5 pancreatic,6 and prostate cancer, 7 foci of epilepsy8 and cardiac arrhythmias.9 In 2002, the FDA approved a monopolar RF device, Thermage® (Solta Medical, Hayward, CA), for the treatment of undesirable facial rhytids. This monopolar application proved popular and was further approved for non-facial applications in 2006.10,11 Since that time, dozens of new RF devices have been developed and approved and studied.
The Physics of Radiofrequency Energy
The term “radiofrequency†refers to electric currents that oscillate between 3 Hz and 3,000 GHz. Within this spectrum are
bands that transmit AM (300kHz), FM, and television (30-300 MHz) signals. Medical RF devices generate electromagnetic radiation at frequencies ranging from 3kHz to 300MHz. When RF energy is passed into tissue charged molecules and ions collide, resistance12 is created. Tissue resistance transforms electrical energy into heat, which is the mechanism by which the desired cosmetic and medical outcomes are achieved. The goal range for heating the dermis is approximately 40-45 degrees Celsius. At this temperature it is known that fibroblasts produce collagen de novo, which results in clinical tightening.13 Each specific tissue layer has intrinsic resistance that must be considered by manufacturers to determine the properties of each application.
Cosmetic Applications of Radiofrequency Energy
There are many different radiofrequency platforms and devices on the market. Each device has unique features, properties, advantages and disadvantages. Cosmetic radiofrequency devices can be broken into three primary categories: monopolar, unipolar, and bipolar. In this review, we will provide an overview of each category and review many of the current products and highlight their various features.
Monopolar Radiofrequency Devices
The development of nonablative, monopolar RF (MRF) devices have helped shift the paradigm of rhytid reduction away from invasive surgery and extensive ablation. Since the first FDA approval, several monopolar devices have been marketed and several of these are summarized in Table 1. The Thermage® device, previously named ThermaCool®, is a monopolar RF system utilizing two terminals: a handpiece that delivers the RF energy to the skin and a grounding pad to complete the circuit.14 Similar to other cosmetic devices, the principle behind ThermaCool is volumetric or bulk heating of the dermis. A cryogen spray
