Dosimetry of Magnetic Fields in the Radiofrequency Range

Abstract

Two therapeutic applications of time varying pulsed electromagnetic fields (EMF) became popular in the last three decades. Both provide a non-invasive no-touch means of applying EMF signals that are detectable at the cell/tissue level [1, 2]. The EMF currently used in orthopedics consist of low frequency signals, with maximum induced electric fields in the mV/cm and the induced current density in the range of several μA/cm². Therefore, the induced secondary magnetic field has a negligible effect on the value of the induced electric field and the resulting magnetic field is relatively independent of the presence of a cell/tissue load. The second therapeutic EMF modality utilizes a short wave pulsed radio frequency (PRF) signal of 27.12 MHz sinusoidal waves. This classical diathermy signal is known to produce heat when applied in continuous mode. In recent applications for reduction of pain and edema the 27.12 MHz sinewave signal is pulsed as 65 µs pulse burst with a repetition rate of 80-600 pps and a peak magnetic field of 2 Gauss. The low duty cycle (less than 4%) assures the minimal elevation of temperature (< 1^°C for 30 min treatment period). Therefore, the accumulated heat in the target tissue is negligible and no dosimetry related to temperature measurements can be applied. Pulsed radiofrequency (PRF) electromagnetic fields (EMF) have been increasingly used clinically to treat a variety of conditions including soft tissue injuries, wounds and burns.