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Microwave-Induced Temperature Gradients In The Rat Brain

The ability to mathematically describe the relationship between radiofrequency (RF) exposure conditions and tissue temperature distributions is important to extrapolating animal data to man, and to establishing safe exposure conditions. Exposure to hgh-powered microwave (HPM) fields is known to produce non-uniform heating in . laboratory animals. The temperature fields which result from exposure depend on a number of variables, including the RF power density and frequency, subject orientation with respect to the field, time duration and mode (CW, pulsed or modulated). In addition, anatomical factors such as tissue permittivity, thermal diffusivity, and local blood perfusion, may profoundly affect the temperature field. Temperature measurements in the brains of rats exposed to 2.45 GHz irradiation over a 30-minute period demonstrated significant tissue heating (Ward, et al., 1986). However, the brain temperature elevation was fairly uniform, with no observable ‘hot spots’ despite the fact that the energy absorption patterns are highly nonuniform at that frequency. The temperature Uniformity was attributed to the brain’s high perfusion rate which makes it difficult to sustain large temperature gradients .