Study type: Medical/biological study (experimental study)

Acute dosimetry and estimation of threshold-inducing behavioral signs of thermal stress in rabbits at 2.45-GHz microwave exposure. med./bio.

Published in: IEEE Trans Biomed Eng 2010; 57 (5): 1234-1242

Aim of study (acc. to author)

To clarify the relationship between whole body average specific absorption rate (SAR) and the rectal temperature elevation in rabbits and to estimate the threshold for inducing a behavioral sign due to microwave provoked thermal stress.The main aim of the study also was to conduct acute dosimetry for high thermal loads due to microwave energy (the experimental conditions were determined with a computational code for electromagnetic-thermal dosimetry via a numeric rabbit phantom).

Background/further details

Rabbits were chosen because of their high susceptibility to heat stress, since they have few sweat glands, and experience difficulty in eliminating excess body heat.
The study was performed with 14 unanesthetized and 10 anesthetized rabbits.
In the current international guidelines for human exposure to microwaves, the limit value is determined by the whole body average SAR value. Although it is known that absorbed microwave energy causes the behavioral sign of thermal stress, the relationship of whole body average SAR with temperature/temperature elevation has not been sufficiently investigated.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Exposure duration: until the core temperature of the rabbit reached 41.5 °C
Exposure 2: 2.45 GHz
Exposure duration: until the core temperature of the rabbit reached 41.5 °C

General information

24 experiments were performed first on anesthetized (10) and then on unanesthetized (14) rabbits. The article does not say how many rabbits were exposed to the individual exposure conditions.

Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Charakteristic
Exposure duration until the core temperature of the rabbit reached 41.5 °C
Exposure setup
Exposure source
Distance between exposed object and exposure source 1 m
Setup rabbit placed in a 10 m x 8 m x 6.5 m anechoic chamber with the bottom of the chamber covered with absorber material; rabbit positioned so that it was irradiated from the lateral side
Parameters
Measurand Value Type Method Mass Remarks
power density 100 W/m² spatial average calculated - incident power density
power density 220 W/m² spatial average calculated - incident power density
SAR 1.18 W/kg average over mass calculated whole body for an incident power density of 100 W/m²
SAR 1.3 W/kg average over mass calculated whole body SAR value that caused behavioral signs of stress

Exposure 2

Main characteristics
Frequency 2.45 GHz
Type
Charakteristic
Exposure duration until the core temperature of the rabbit reached 41.5 °C
Exposure setup
Exposure source
Distance between exposed object and exposure source 1.2 m
Setup rabbit placed in a 10 m x 8 m x 6.5 m anechoic chamber with the bottom of the chamber covered with absorber material; rabbit positioned so that it was irradiated from the lateral side
Parameters
Measurand Value Type Method Mass Remarks
power density 730 W/m² spatial average calculated - incident power density
power density 980 W/m² spatial average calculated - incident power density
SAR 1.18 W/kg average over mass calculated whole body for an incident power density of 100 W/m²
SAR 1.3 W/kg average over mass calculated whole body SAR value that caused behavioral signs of stress

Reference articles

  • Wake K et al. (2007): Development of a 2.45-GHz Local Exposure System for In Vivo Study on Ocular Effects.
  • Hirata A et al. (2006): Computational verification of anesthesia effect on temperature variations in rabbit eyes exposed to 2.45 GHz microwave energy.
  • Spiegel RJ (1984): A Review of Numerical Models for Predicting the Energy Deposition and Resultant Thermal Response of Humans Exposed to Electromagnetic Fields.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

The data suggest that a core temperature elevation of 1°C is an estimate of the threshold inducing complex behavioral signs of microwave-induced thermal stress in rabbits for different whole body exposure average SAR values and exposure durations. The whole body exposure average SAR value required for microwave-induced behavioral signs in rabbits was estimated as approximately 1.3 W/kg for 2.45 GHz microwaves.

Study character:

Study funded by

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