Topic

Investigation of SAR distribution in laboratory animals exposed to electromagnetic fields

Start

15.12.1999

End

31.12.2002

Project Management

Integrated Systems Laboratory
Swiss Federal Institute of Technology, Zurich

Objective

The distribution of specific absorption rates (SAR) in the bodies of exposed test animals is to be determined with the help of numerical methods. A high resolution, spatial SAR distribution in man is to be used for comparison. Exposure conditions similar to far field exposure conditions in current standard exposure chambers or TEM cells, respectively, are to be applied. Model spatial resolution should be as fine as possible, e.g. by using magnetic resonance imaging (MRI). Minimum requirement for the animal model is a resolution of 1 mm³. Technical widespread frequencies and various model orientations in the field have primarily been studied. The specified frequencies were 450 MHz, 900 MHz, 1,8 GHz and 5 GHz. The project was divided into three work packages. In the first work package, computer models needed for a numerical examination were developed both for laboratory animals (rats and mice) and human beings. Model data of internal body structure were collected and linked to dielectric parameters typical of the respective tissues. In the second work package, these models were exposed to currently applied technical fields and SAR values in the body were determined numerically. In the third work package, a comparison between the results of the simulation and the measurements of the models was made based on the animal model.

Results

An improved method for creating voxel models was developed (a voxel can be pictured as a small, homogeneous cube. A voxel model simulates a real body by means of small cubes). The newly developed voxel models achieved a very high resolution: approx. 0,06 mm³ for the mouse, 0,2 mm³ for the rat and 8 mm³ in the human being. These resolutions are the highest achieved in animal models to date. More than 100 types of organs or tissues were differentiated in the voxel models and very realistic computer models have been developed. In application of these computer models, quantitative results on the expected SAR distribution in laboratory animals depending on the parameters of the applied electromagnetic fields have been obtained. In addition to the SAR values averaged over the whole body, organ-specific SAR values have also been determined and presented in tabular form. Limits of numerical simulation have also been determined. Limitations depending primarily on model resolution and, therefore, on computer capacity and memory. Consequently, for example, at 5GHz, there was no point in carrying out SAR distribution in the human model. Calculation verification as compared to measurements of simpler models (fluid-filled tubular bodies) showed higher than 30% conformity. The comparison of model calculations in an animal cadaver, however, showed a deviation of more than a factor of 2. When using voxel models based on whole body averages, the comparison between model calculation and the measurement of an animal carcass showed good agreement. Comparing results using the previously standard homogeneous ellipsoidal models resulted in deviations of up to a factor of 2.

The final report with a reduced resolution of the included picture can be downloaded as PDF-file in German (3506 kB).

Conclusions

The results are an important contribution to evaluating dosimetry as it relates to questions of radiation protection. Essential parameters influencing variation of results and bands of accuracy were pointed out. The results have particular importance in the future performance of animal experiments as they define essential details of the dosimetric boundary conditions to be taken into account, respective of investigated endpoints and animal models. They also highlight differences in absorption behaviour in human beings, which must be considered when transferring results to man. In addition, the results are used in dosimetric considerations and for decisions about future project designs in the German Mobile Telecommunication Research Programme (DMF).