Publications (2)2.83 Total impact
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Article: Computational modeling of temperature elevation and thermoregulatory response in the brains of anesthetized rats locally exposed at 1.5 GHz.
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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.Physics in Medicine and Biology 11/2011; 56(23):7639-57. · 2.83 Impact Factor -
Article: Computational Model of Temperature Elevation in Rats Exposed to Intense and Localized Exposure at 1.5 GHz
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ABSTRACT: INTRODUCTION There has been increasing public concern about the adverse health effects of human exposure to electromagnetic waves. In the radiofrequency and microwave (MW) ranges, elevated temperature (1-2 o C) resulting from energy absorption is known to be a dominant factor inducing adverse health effects such as heat exhaustion and heat stroke. Whole-body average specific absorption rate (SAR) is used as a measure of human protection for MW whole-body exposure. Thresholds are based on the fact that MW exposure of laboratory animals in excess of approximately 4 W/kg has revealed a characteristic pattern of thermoregulatory response. Peak spatially averaged SAR is used as a metric for localized exposure, but the rationale for the use of SAR as a metric for local exposure has been challenged, especially with respect to local and systemic physiological responses, including change in blood perfusion. In order to obtain some insight on the effect of localized exposure, our group has conducted exposures of rats. Our previous studies had failed to show blood flow changes in pial microcirculation in the brain of rats locally exposed to 1,439 MHz RF even at 4.8 W/kg brain averaged SAR (e.g., [1]). On the contrary, a recent study reported that the blood flow in the human brain increased after the exposure to pulse-modulated 900 MHz RF at 0.27 W/kg brain averaged SAR [2]. In the present study, we simulate the exposure scenario of the measurement in [3] in order to investigate the time course of temperature elevation due to microwave exposure. MODELS AND METHODS Male Sprague-Dawley rats (4 weeks old) were used in the experiment. The rats were anesthetized with an intramuscular injection of ketamine (100 mg/kg) and xylazine (10 mg/kg), and with a subcutaneous injection of pentobarbital (12.5 mg/kg). The core temperature was maintained at 36±0.4°C in sham exposure using a heating pad (42°C) to avoid the reduction in basal metabolism under anesthesia. The heads of the animals were fixed in a stereotaxic apparatus and locally exposed to 1,457 MHz microwave emitted from an "8"-shaped loop antenna. The exposure duration was six minutes. This exposure setup is shown in Fig. 1. For computing EM absorption in the rat, the Finite-Difference Time-Domain (FDTD) method was used. Then, the temperature variation was computed by solving the bioheat equation along with the SAR computed by the FDTD method.
