Authors
McIntosh RL, Deppeler L, Oliva M, Parente J, Tambuwala F, Turner S, Winship D, Wood AW. Comparison of radiofrequency exposure of a mouse dam and foetuses at 900 MHz. Phys Med Biol. Jan 28, 2010 55(4):N111-N122. Ahead of print.

Introduction
Studies of biological effects of radiofrequency (RF) exposure require detailed and accurate dosimetric data for correct interpretation of their outcomes. Some recent studies of possible adverse effects of RF exposure on mouse foetuses use a radial cavity exposure system. These studies did not involve pregnant mice and local exposure assessment. The finite-difference time-domain (FDTD) method makes it possible to handle complex heterogeneous geometrical structures and assess localized exposures. Mathematical models of various animals’ anatomy (rats, rhesus monkey, pigmy goat) including models of pregnant rats, rat foetuses and newborn rats have been developed for exposure assessment. Some models of rat and mouse, including pregnant versions, are commercially available. However, further developments are needed in this area in order to provide more accurate data for RF dosimetry studies.

Objective
The objectives of this study were the following: “to develop high resolution, anatomically accurate male, female, pregnant female and fetus models” and, based on the pregnant mouse model, to compare the exposure of the dam and the fetuses in terms of SAR and resulting temperature changes.

Methods
The mouse anatomical models were developed using FDTD numerical techniques. Tissue types and morphology for modeling were identified based on sectional anatomical photographs from a detailed colored anatomical atlas. Two different RF exposure conditions for pregnant mice, a radial cavity exposure system operated at 900 MHz and a 900 MHz plane wave exposure, were simulated. Induced SAR in the mouse model was calculated using the commercially available FDTD software.. A finite-difference program based on Pennes’ bioheat equation was used to determine the temperature increase due to induced SAR.

Results and Interpretation
For the exposure in the radial cavity system, the whole-body average SAR in the foetuses was about 14% (on the average) lower than the whole-body average SAR in the dam. The peak temperature increase due to the SAR was significantly (45%) lower in the fetuses than in the dams. For the plane wave exposures, the whole-body average SAR in the foetuses was about 17% lower and the peak temperature increase – about 55% lower than in the dams. The analyses were conducted to determine the influence of the higher water content of the foetal tissues. For this purpose, the plane wave exposure conditions were used, and computations were conducted assuming equal water content values in fetuses and in adult animals. Under the assumption of equal water content, the average SAR in the fetuses was about 40% lower than that in the dams; the peak increase in temperature was about 55% lower than in the dams.

Conclusion
The results of this study can be used to determine power levels required to produce given exposure levels in the mouse foetuses. The allowance for higher water content in the foetal tissues is important in calculations of SAR values and temperature changes.


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