Computational modeling of temperature elevation and thermoregulatory response in the brains of anesthetized rats locally exposed at 1.5 GHz

Abstract

The dominant effect of human exposures to microwaves is caused by temperature elevation ('thermal effect'). In the safety guidelines/standards, the specific absorption rate averaged over a specific volume is used as a metric for human protection from localized exposure. Further investigation on the use of this metric is required, especially in terms of thermophysiology. The World Health Organization (2006 RF research agenda) has given high priority to research into the extent and consequences of microwave-induced temperature elevation in children. In this study, an electromagnetic-thermal computational code was developed to model electromagnetic power absorption and resulting temperature elevation leading to changes in active blood flow in response to localized 1.457 GHz exposure in rat heads. Both juvenile (4 week old) and young adult (8 week old) rats were considered. The computational code was validated against measurements for 4 and 8 week old rats. Our computational results suggest that the blood flow rate depends on both brain and core temperature elevations. No significant difference was observed between thermophysiological responses in 4 and 8 week old rats under these exposure conditions. The computational model developed herein is thus applicable to set exposure conditions for rats in laboratory investigations, as well as in planning treatment protocols in the thermal therapy.

Comparison of Thermal Response for RF Exposure in Human and Rat Models

“…The computational rat model (8-week-old rat) was developed from computed tomography (CT) images [7]. The rat model was composed of the following six tissues: muscle, skin, fat, eye, bone, and brain.…”

“…The blood perfusion in the brain was given as follows, based on our rat measurements for local RF exposure [7]:$B\left(boldnormalr,t\right)=B_0\left(r\right)\left(1+F_{HS}\Delta T_H\left(t\right)\right)·2^{\Delta T\left(r\right)/F_{BB}},$ where F HB (=0.053 °C −1 ) and F BB (=13.9 °C) denote weighting coefficients in relation to the variations in the core and brain temperature elevations, respectively [25]. …”

“…This was partly because of ethical reasons. To the best of our knowledge, only the authors’ group has developed a computational code for temperature computation in animals, taking into account their thermoregulation [6,7]. Even for humans, only a few groups have succeeded in this [8,9,10,11].…”

“…In our previous studies, an integrated computational technique, combining electromagnetics and thermodynamics, was developed by incorporating a thermoregulatory response model based on measured values [7,25]. This study aims to clarify the difference of the temperature elevation and its time course between rats and humans exposed to local RF fields, which is important to estimate how conservative the current limits are for local exposure in the international guidelines/standards.…”

Development of computational small animal models and their applications in preclinical imaging and therapy research

“…Following this study, animal SAR values were calculated and reported for mouse, rat, rabbit, and pig under RF exposures of 800 MHz-2 GHz cellular phone electromagnetic fields. 22,36,44,54,[113][114][115][116][117][118][119][120][121][122][123] Dosimetry calculations were performed for the exposure of mice and rabbit to 2.45 GHz WiFi frequencies. [124][125][126][127][128][129] Fig.…”