High-frequency electromagnetic field distribution indicator for medical use

Abstract

therapeutic procedure is a part of the HF-system, are major sources of parasitic electromagnetic radiation [6]. Under local treatment by a remote source of electromagnetic radiation, up to 75% of electromagnetic wave energy may be reflected and scattered on the skin surface [10]. UHF-therapy is a particularly intensive source of parasitic radiation because a considerable fraction of the applied energy is scattered in the circumelectrode space, where the treated part of the patient's body is exposed [6]. It is known that even under weak thermal UHF-treatment, long-standing parasitic radiation may cause an oscillation effect [6] and affect biological processes by breaking hydrogen bonds, reorienting DNA and RNA molecules [10], and overheating biological tissues with insufficient circulation (e.g., eye lens, vitreous body, etc.) [10]. However, alternating parasitic magnetic fields are most dangerous because even at relatively low magnetic induction but sufficiently long exposure time they may unfavorably affect medical personnel constantly working with this equipment [2, 8]. During inductothermal therapy the patient's body tissues are exposed to the HF magnetic field generated by an electric current passing through a flexible cable coiled as a helix around the part of the patient's body intended for treatment. The efficacy of the therapy increases with magnetic field frequency [6]. Such treatment and apparatuses for microwave therapy, where the patient's body is exposed to alternating SHF magnetic field, generate little if any parasitic radiation. However, SHHF-tberapy is associated with another problem: indication of output SHF energy of the medical therapeutic device. Common neon lamps, which are effectively used as pilot lamps in UHF apparatuses, fail to detect low-intensity SHF radiation. Thus, the development of devices for detecting parasitic electromagnetic radiation generated by medical therapeutic apparatuses and for indicating the spatial distribution of therapeutic SHF electromagnetic fields is an important problem. It should be noted that not only the electromagnetic field indication but also the distribution of its intensity should be measured because this allows work places to be located taking into account potentially harmful effects of stray electromagnetic radiation. A device for detecting HF electromagnetic field distribution has been developed at the Department of Medical and Biological Physics, Rostov State Medical University. The device was designed not only to indicate the presence of electromagnetic field, but also to measure spatial distribution of both electric and magnetic components of electromagnetic field and to provide optimum use of UHF and SI--IF therapeutic devices. The device operates on the principle of electromagnetic radiation-induced increase of the conductivity of normal glow self-discharge. Normal glow self-discharge is ignited in a tiny neon lamp connected as an arm of a four-arm measuring resistor bridge (Fig. 1). A microammeter is connected to the diagonal of the bridge to indicate external electromagnetic field and to measure (after preliminary calibration) its strength. The neon lamp is connected to the circuit by a long cable, which allows the lamp to be placed at the point of interest and to be used as an electromagnetic field probe.