A.B. Gapeyev, N.K. Chemeris

The review considers some questions of dosimetry which solution is necessary at studying the mechanisms of biological effects of extremely high-frequency electromagnetic radiation. The purpose of dosimetry is the establishment of relationship between parameters of external electromagnetic fields influencing a biological object and parameters of the fields penetrating into or arising in the exposed system which lead to primary biological effects. In spite of the large number of works in the field of electromagnetic biology and therapy, the correct dosimetric supply is rather an exception than a rule. This results in both irreproducibility and inaccurate interpretation of experimental results. On the basis of our own results and literature data, the dosimetry methodology is demonstrated at choosing a radiating system, providing the matching of a radiator with feeding tract and irradiated biological object, measuring the radiation pattern of an antenna, determining an incident power density, measuring a distribution of the specific absorption rate in irradiated object, assessing a degree of heterogeneity of the specific absorption rate, dependence on radiation frequency and geometry of irradiated object. Results of testing of various types of antennae show the following. First, at an exposure of biological objects in the near field zone of horn antennae, there is complex multiple-mode interference pattern of an electromagnetic field distribution in an object plane that can lead to artefacts at studying an effect dependence on the frequency and power. Second, dielectric antennae, as a rule, have the poor matching with feeding tract; the value and character of dependence of a standing wave ratio on frequency are determined by both a configuration of the antenna and a distance to irradiated object. Therefore, irradiating the object by means of the dielectric antenna, it is necessary to have accurate notion about the specific absorption rate, its spatial distribution and dependence on radiation frequency. An antenna of a special form developed by us, the channel radiator, is free from the limitations inherent to horn and dielectric antennae that allows to use it effectively for biomedical studies. The channel radiator provides a good directivity, uniformity of electromagnetic field in an object plane, and a good matching with feeding tract that allows carrying out an exposure of biological objects with the help of the channel radiator in both the near and far field zones. Examples of experimental, theoretical and numerical methods of determination of electromagnetic energy absorption are submitted for in vitro and in vivo irradiation of biological systems. Specific absorption rate in the skin of laboratory animals was determined on the basis of both microthermometric measurements of initial rates of temperature rise in the skin induced by exposure and microcalorimetric measurements of specific heat of the skin. Theoretical calculations of SAR in the skin were performed taking into account dielectric parameters of the skin obtained from standing wave ratio measurements at reflection of electromagnetic waves from the skin surface, and considering effective area of stationary overheating measured by a method of infrared thermography. The numerical method was developed to determine electromagnetic energy reflected, absorbed and transmitted in the model of flat layers. An algorithm of the method was realized in computer program and used to calculate SAR in the skin on the basis of complex dielectric constant of skin. The SAR values obtained from experimental measurements, theoretical calculations and numerical analysis are in good mutual correspondence. The results can be used for dosimetric supply of biomedical experiments on studying physicochemical mechanisms of biological effects of extremely high-frequency electromagnetic radiation. In spite of complexity at implementation of dosimetry in a range of extremely-high frequencies, the knowledge of its features and methods of measurement and an assessment of the physical values characterizing electric, magnetic and electromagnetic fields should become the mandatory requirement. Without the solution of dosimetry problems, the investigation into the mechanisms of biological effects of electromagnetic radiation becomes incorrect. It is necessary to determine and specify all parameters of the electromagnetic field and exposure conditions, since change of the majority of them can cardinally modify re-sponse of a biological system. Inconsistent or incomplete dosimetric supply and absence of necessary controls imply an occurrence of artefacts, difficulties for the analysis of experimental results and undervaluation of even the most interesting and important effect of electromagnetic radiation.