Biological effects due to whole-body radio-frequency exposure may be induced by core temperature elevation. According to the international safety guidelines/standards for human protection, the whole-body averaged specific absorption rate (WBA-SAR) is used as a metric. In order to understand the relationship between WBA-SAR and core temperature elevation, a theoretical solution or a closed formula for estimating core temperature elevation is essential. In the present study, we derived a formula for simply estimating core temperature elevation in humans and animals due to whole-body radio-frequency exposure. The core temperature elevation estimated with the formula is found to be in reasonable agreement with the computational results of finite-difference time-domain computation incorporated in anatomically-based models. Based on the formula, the WBA-SAR is found to be a good metric for estimating core temperature elevation. The main factors influencing the core temperature elevation are the perspiration rate and the body surface area-to-weight ratio.
2. ICNIRP, "International commission on non-ionizing radiation protection guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz)," Health Phys., Vol. 74, No. 4, 494-522, Apr. 1998.
3. IEEE, "IEEE standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3 kHz to 300 GHz,", C95-1, 2005.
4. Michaelson, S. M., "Biological effects and health hazard of RF and MWenergy; fundamentals and overall phenomenology," Biological Effects and Dosimetry of Nonionizing Radiation, 337-357, Press, New York, 1983.
5. D'Andrea, J. A., J. R. DeWitt, O. P. Gandhi, S. Stensaas, J. L. Lords, and H. C. Neilson, "Behavioral and physiological effects of chronic 2450-MHz microwave irradiation of the rat at 0.5mW/cm2," Bioelectromagnetics, Vol. 7, 45-56, 1986.
6. Adair, E. R. and D. R. Black, "Thermoregulatory responses to RF energy absorption," Bioelectromagnetics Suppl., Vol. 6, S17-S38, 2003.
7. Guidance for the submission of paremarket notifications for magnetic resonance diagnostic devices, Center for Devices and Radiologic Health, Food and Drug Administration, Rockville, MD, 1998, http://www.fda.gov/cdrh/ode/guidance/793.html.
8. Hirata, A., T. Asano, and O. Fujiwara, "FDTD Analysis of body-core temperature elevation in children and adults for whole-body exposure," Phys. Med. Biol., Vol. 53, 5223-5238, 2008.
9. Hirata, A., H. Sugiyama, M. Kojoma, H. Kawai, Y. Yamashiro, O. Fujiwara, S. Watanabe, and K. Sasaki, "Computational model for calculating body-core temperature elevation in rabbits due to whole-body exposure at 2.45 GHz," Phys. Med. Biol., Vol. 53, 3391-3404, 2008.
10. Fiala, D., K. J. Lomas, and M. Stohrer, "Computer prediction of human thermoregulation and temperature responses to a wide range of environmental conditions," Int. J. Biometeorol., Vol. 45, No. 3, 143-159, 2001.
11. Stolwijk, J. A. J. and J. D. Hardy, "Control of body temperature," Handbook of Physiology, Section 9, Reactions to Environmental Agents, H. K. Douglas (ed.), 45-69, American Physiological Society, Bethesda, MD, 1977.
12. Foster, K. R. and E. R. Adair, "Modeling thermal responses in human subjects following extended exposure to radiofrequency energy," Biomed. Online, Vol. 3, 4, 2004.
13. Nagaoka, T., S. Watanabe, K. Sakurai, E. Kunieda, S. Watanabe, M. Taki, and Y. Yamanaka, "Development of realistic high-resolution whole-body voxel models of Japanese adult male and female of average height and weight, and application of models to radio-frequency electromagnetic-field dosimetry," Phys. Med. Biol., Vol. 49, 1-15, 2004.
14. Nagaoka, T., E. Kunieda, and S. Watanabe, "Proportion-corrected scaled voxel models for Japanese children and their application to the numerical dosimetry of specific absorption rate for frequencies from 30MHz to 3 GHz," Phys. Med. Biol., Vol. 53, 6695-6711, 2008.
15. Wake, K., H. Hongo, S. Watanabe, M. Taki, Y. Kamimura, Y. Yamanaka, T. Uno, M. Kojima, I. Hata, and K. Sasaki, "Development of a 2.45-GHz local exposure system for in vivo study on ocular effects," IEEE Trans. Microwave Theory & Tech., Vol. 55, 588-596, 2007.
16. Taflove, A. and S. Hagness, Computational Electrodynamics: The Finite-difference Time-domain Method, 3rd Ed., Artech House, Norwood, MA, 2003.
17. Gabriel, S., R. W. Lau, and C. Gabriel, "The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues," Phys. Med. Biol., Vol. 41, 2271-2293, 1996.
18. Bernardi, P., M. Cavagnaro, S. Pisa, and E. Piuzzi, "Specific absorption rate and temperature elevation in a subject exposed in the far-¯eld of radio-frequency sources operating in the 10-900-MHz range," IEEE Trans. Biomed. Eng., Vol. 50, 295-304, 2003.
19. Wainwright, P. R., "The relationship of temperature rise to specific absorption rate and current in the human leg for exposure to electromagnetic radiation in the high frequency band," Phys. Med. Biol., Vol. 48, 3143-3155, 2003.
20. Bit-Babik, G., A. Faraone, C.-K. Chou, A. Radmadze, and R. Zaridze, "Correlation between locally averaged SAR distribution and related temperature rise in human body exposed to RF field," Proc. BEMS 2007, 2-5, 2007.
21. Pennes, H. H., "Analysis of tissue and arterial blood temperatures in resting forearm," J. Appl. Physiol., Vol. 1, 93-122, 1948.
22. Follow, B. and E. Neil, Circulation, Oxford Univ. Press, New York, USA, 1971.
23. Mohsin, S. A., N. M. Sheikh, and U. Saeed, "MRI induced heating of deep brain stimulation leads: Effect of the air-tissue interface," Progress In Electromagnetics Research, Vol. 83, 81-91, 2008.
24. Hirata, A., S. Watanabe, M. Kojima, I. Hata, K. Wake, M. Taki, K. Sasaki, O. Fujiwara, and T. Shiozawa, "Computational veri¯cation of anesthesia effect on temperature variations in rabbit eyes exposed to 2.45-GHz microwave energy," Bioelectromagnetics, Vol. 27, 602-612, 2006.
25. Ibrahiem, A., C. Dale, W. Tabbara, and J. Wiart, "Analysis of the temperature increase linked to the power induced by RF source," Progress In Electromagnetics Research, Vol. 52, 23-46, 2005.
26. Liu, Y., Z. Liang, and Z. Yang, "Computation of electromagnetic dosimetry for human body using parallel FDTD algorithm combined with interpolation technique ," Progress In Electromagnetics Research, Vol. 82, 95-107, 2008.
27. Hirata, A., K. Shirai, and O. Fujiwara, "On averaging mass of SAR correlating with temperature elevation due to a dipole antenna ," Progress In Electromagnetics Research, Vol. 84, 221-237, 2008.
28. Foster, K. R. and R. Glaser, "Thermal mechanisms of interaction of radiofrequency energy with biological systems with relevance to exposure guidelines ," Health Phys., Vol. 92, 609-620, 2007.
29. Hoque, M. and O. P. Gandhi, "Temperature distribution in the human leg for VLF-VHF exposure at the ANSI recommended safety levels ," IEEE Trans. Biomed. Eng., Vol. 35, 442-449, 1988.
30. Spiegel, R. J., "A review of numerical models for predicting the energy deposition and resultant thermal responses of humans exposed to electromagnetic fields," IEEE Trans. Microwave Theory & Tech., Vol. 32, 730-746, Aug. 1984.
31. Marai, I. F. M., A. A. M. Habeeb, and A. E. Gad, "Rabbits' productive, reproductive and physiological performance traits as affected by heat stress: A review," Livestock Prod. Sci., Vol. 78, 71-90, 2002.
32. Ebert, S., S. J. Eom, J. Schuderer, U. Spostel, T. Tillmann, C. Dasenbrock, and N. Kuster, "Response, thermal regulatory threshold of restrained RF-exposed mice at 905 MHz," Phys. Med. Biol., Vol. 50, 5203-5215, 2005.
33. Nakayama, T. and M. Iriki, "Physiology of energy exchange and thermoregulation," Handbook of Physiological Science, Vol. 18, Igaku-Shoin Ltd., Tokyo, 1987.
34. Wang, J., S. Kodera, O. Fujiwara, and S. Watanabe, "FDTD calculation of whole-body average SAR in adult and child models for frequencies from 30MHz to 3 GHz," Phys. Med. Biol., Vol. 51, 4119-4127, 2005.
35. WHO RF research agenda, 2006.