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The Basic Science of Radiofrequency-Based Devices

The basic science and specific principles of operation for radiofrequency (RF) technologies with a focus on minimally-invasive applications enhancing liposuction procedure. Before discussing the parameters, settings and techniques for radiofrequency-assisted lipolysis (RFAL) and fractional RF subdermal treatment, it is important to understand the fundamentals of the basic science of RF technologies and applications. The chapter accurately describes the physics of the processes occurring during RF-based treatment, and the factors affecting its safe and efficacious outcome. The discussion of RF-based devices will use terminology and definitions provided by FDA guidance for electrosurgical devices. Measurements and computer simulations conducted by the authors to illustrate importance of different parameters for the specific treatments of skin and subcutaneous fat are also presented.

1. RF treatment effect

The method of operation for the vast majority of esthetic energy-based devices (EBD’s) is through the generation of heat causing physiologic modifications to the human tissue. RF energy is a method to deliver heat into the human body at a level and distribution required for the specific application. For sub-necrotic thermal applications, this heat can be a relatively low temperature for fibroblast stimulation and metabolism acceleration (hands free RF devices). Alternatively, the heat can be more aggressive, ablative coagulative and necrotic in nature (RF assisted lipolysis or Fractional micro-needling technology). It may occur that during the same treatment, RF energy effects will be both non-ablative on the skin and ablativecoagulative sub-dermally. In most instances with RF, microwave and light-based technologies, heat is the result of a common pathway for the desired thermal effects. This understanding has given rise to an entire generic category of esthetic and medical EBD’s. A variety of technologies and devices have been developed based on thermal treatment of tissue, either ablative or non-ablative, selective, or non-selective, using optical energy, RF electrical current, focused ultrasound to generate the heat. The common outcome of these devices leads to some heat-assisted transformation of local tissue. This thermally stimulated tissue alteration or remodeling typically results from:

  • Selective thermal targeting of tissue by focusing energy at the desired spot internally or externally. Energy can be delivered to the selected volume in a minimally invasive manner by focusing energy to penetrate the tissue under the skin surface. An example of a minimally invasive treatment is electro-surgical devices which deliver thermal energy into the body via a tiny cannula or needle. Alternatively, electrocautery devices focus the energy on the tissue surface, ablating the tissue in proximity of the tip of the instrument to dissect the a soft tissue.
  • Non-selective bulk heating, used mostly for sub-necrotic heating to stimulate natural processes in the body leading to increased production of collagen, elastin and ground substances. The result may include tissue tightening, circumferential reduction and wrinkle reduction. RF energy is an important part of the armamentarium for treatment options comprising tissue cutting and coagulation, minimally invasive selective tissue targeting and bulk heating. RF current is the accepted type of energy used in four out of five surgeries conducted in the world and most industry leaders in the aesthetic field employ RF energy in at least one of their applications.

2. What is electromagnetic energy?

Electromagnetic (EM) energy travels in waves and spans a very broad wavelength spectrum from DC voltage, to very short wavelengths in gamma radiation (Figure 1). RF energy is small part of electromagnetic spectrum having frequencies in the range of Kilohertz to Gigahertz. The shorter wavelength and the higher frequency, the more energetic are quanta of EM radiation and the more destructive it can be for the tissue. RF energy, Microwaves, Infrared and Visible Light has relatively low frequencies and represent non-ionizing radiation which is not able to modify the DNA (genes) inside the cells. High frequency radiation as UV, X-ray and Gamma are ionizing radiation which in natural conditions is generated by plasma or by radiative isotopes.

A very small part of RF spectrum range is used in EBD, and its properties will be the primary focus of the current chapter.

3. The history of RF

RF energy has been used in medicine for over 100 years. Nikola Tesla, (1856– 1943), Croatia-born electrical and mechanical engineer, is reputed as being the father of alternating high frequency current. But it was Dr. William Bovie that developed the first electrosurgical device during the period of 1914–1927 at Harvard University [1]. The first reported use of an electrosurgical generator in an operating room occurred on October 1st, 1926 in a surgery performed by Dr. Harvey Williams Cushing. Since Dr. Bovie introduced RF energy and the electrocautery, RF had been used for ablation [4] and coagulation [5] in surgery and medicine. Over the past 20 years, RF energy has evolved and come to dominate esthetic medicine (for good reasons, as will be explained in this chapter). RF was first being used in non-ablative form for skin collagen remodeling and other esthetic applications.

The early pioneers of RF energy in medicine

4. Radiofrequency in medicine

The specificity of RF energy in medicine is that it acts as an electrical current flowing through the tissue but differently than radiation. RF energy is associated with electro-surgical devices and can be defined as high frequency alternating electrical current heating soft tissue without significant electrical nerve stimulation. It is critical to minimize nerve impact to avoid electric shock which may cause muscle spasm and cardiac arrest. It is important to remember that tissue has ion conductivity with the most prominent varieties being Na+, K+, and Cl– (sodium, potassium, and chlorine ions respectively). Nerves are affected as a result of ion penetration through the membrane of neuron. Under normal conditions the nerve is surrounded by electrically neutral liquid where ions with positive and negative charge compensate each other and bound by Coulomb force preventing free diffusion of the electrical charge. As an electrical field is applied the ion starts to move and the nerve stimulating effect depends on ion displacement (D) in alternating electrical field that can be presented as following:

RF based medical devices are a common tool for plastic surgeons, used during most surgical procedures. RFAL and RF fractional technologies have become important modalities for about 20% of plastic surgeons, for enhancing liposuction results or by its own for patients for whom reduction of adipose compound is not a main esthetic goal. Over the last 100 years extensive knowledge has been acquired about RF technology and RF-tissue interaction. The information in this chapter can help a potential buyer of new equipment make a rational choice, based on goals of treatment and physics of the RF device in question. Even more importantly, expanding the physician’s understanding of his or her devices already in use can maximize treatment outcomes and minimize unwanted side effects and complications.