Generation of Infant Anatomical Models for Evaluating Electromagnetic Field Exposures
Congsheng Li, Zhiye Chen, Lei Yang, Bin Lv, Jianzhe Liu, NadegeVarsier, Abdelhamid Hadjem, Joe Wiart, Yi Xie, Lin Ma, and Tongning Wu. Generation of Infant Anatomical Models for Evaluating Electromagnetic Field Exposures. Bioelectromagnetics 36(1):10–26, 2015.
In this work, we developed one 12-month-old male whole body model and one 17-month-old male head model from magnetic resonance images. The whole body and head models contained 28 and 30 tissues, respectively, at spatial resolution of 1 mm x 1 mm x 1 mm. Fewer identified tissues in the whole body model were a result of the low original image quality induced by the fast imaging sequence. The anatomical and physical parameters of the models were validated against findings in published literature (e.g., a maximum deviation as 18% in tissue mass was observed compared with the data from International Commission on Radiological Protection). Several typical exposure scenarios were realized for numerical simulation. Dosimetric comparison with various adult and child anatomical models was conducted.
Significant differences in the physical and anatomical features between adult and child models demonstrated the importance of creating realistic infant models.
Current safety guidelines for infant exposure to radiofrequency electromagnetic fields may not be conservative.
To protect against radiofrequency (RF) electromagnetic field (EMF) exposure, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published guidelines in 1998 for limiting excessive emission [ICNIRP, 1998]. Basic limits (e.g., specific absorption rate [SAR]) and reference levels (e.g., spatial power density) are used to evaluate RF EMF safety. Compliance with the reference levels is regarded as compliance with the basic limits. Measurement and numerical simulation are frequently used for compliance evaluation ...
... The infant model had the largest proportion of fat (tissue has lower conductivity and, thus, lower power absorption ability). Hence, the WBASAR of the infant model was the smallest among all of the surveyed models. By contrast, at higher frequency (e.g., 450 MHz), the penetration depth decreased to 0.05 m for brain tissues, muscles, and skin, and 0.20 m for bones. Therefore, the EMF power can penetrate deeper into the infant model (in terms of cross-sectional proportion) than into the larger models. Higher EMF powers cannot only deposit in superficial and less lossy layers (e.g., fat), but also in deeper and lossy tissues (e.g., muscles and internal organs) for the infant model. When averaging over the entire body mass, larger models tended to show smaller WBASAR than infant models. In this case, the ICNIRP guidelines may not be conservative for infants...
We reconstructed one whole-body model and one head model from the MR datasets of two 12- and 17-month old infants. The anatomical and physical parameters of these models were validated using data from published literature. We found significant physical differences between the infant models and models from other age groups. A rapid increase in brain mass was observed between the 12- and 17-month-old infant heads, which was not observed in other age groups. Three RF EMF exposure scenarios were established. Results revealed that safety limits prescribed in ICNIRP guidelines might not be conservative for infants. The individual anatomy of infants may significantly influence localized SAR. These findings confirm the necessity of filling the gaps between human anatomical models for evaluating EMF exposure effects. Simulation results covering larger frequency bands and exposure scenarios using the present models will be published in future reports.
Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley
Electromagnetic Radiation Safety
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