ID Number		333
Study Type		Engineering & Physics
Model		915 MHz (GSM) exposure and modeling of SAR distribution and surface heating using vascularized human FDTD models (including child vs. adult, eye)
Details		Human models used to calculate SARs at the head surface as well as in the deeper tissues of the brain by FDTD calculations using a model that included heat dissipation from blood vessels. The authors also verified skin temperature measurements with small thermocouple probes. They found that at max power (900 MHz, 250 mwatts avg, GSM), they calculated peak SARs of over 4 W/kg in some small muscle voxels in their FDTD calculations, but that the average over 1 gram of tissue in this region was 1.53 W/kg, and within 10 grams was 0.91 W/kg (within both US and European (ICNIRP) safety standards). In a subsequent paper (2002) the authors calculated SARs of 1.72 W/kg over 1 g avg and 0.98 W/kg over 10 g avg using a female head model. In verifying temperature increases, they found increases of 0.11 degrees C or below, mainly at the skin surface. They also calculated that the phone power would have to be increased to 6.8 watts average (it is currently set a 250 milliwatts average) to get a temperature rise of 3 degrees in the head, a level which must be achieved before significant biological damage would occur. The authors state that "Although these power distributions are not in compliance with all proposed safety standards, temperature rises are far too small to have lasting effects". The authors also performed studies to look at different effects of head size on mobile phone RF energy absorption (i.e., child vs. adult).In recent studies (2005), a high-resolution model of the human eye, including 21 different tissues and complete vascular structure, was developed for thermal modeling. The authors report that constant heat transfer coefficients previously determined from simplier human and rabbit eye models underestimate the actual value, suggesting that it is much more difficult to heat the eye, and the cooling ability of the vasculature more effective, than previously assumed. They conclude that the bioheat approach (as opposed to the heat transfer coefficient initially determined for heat transfer from sclera to body core) is appropriate for a first order approximation of temperature distribution due to RF heating at a homogeneous power density, but discrete vasculature on the order of 0.2 mm in diameter must be accounted for if temperature differences on a mm scale are of interest. Subsequent studies using a detailed and vascularized model of the human eye and orbit showed averaged SAR over the eye of 1.7, 2.5, and 2.2 W/kg for 900, 1500, and 1800 MHz (respectively) resulted in peak SARs in the humor of 4.5, 7.7, and 8.4 W/kg and a corresponding max temperature rise of 0.22, 0.27, and 0.25 degrees C. Although a simple linear extrapolation of avg SAR over 10 grams is not entirely appropriate, using such an extrapolation as a crude estimation from the above data might suggest a temperature rise of greater than 1 degree C at the occupational limit (10 W/kg over 10 grams - or the entire eyeball). Position of max temp at 900 MHz was the anterior lens, for 1500 MHz was the posterior lens, and for 1800 MHz was the encter of the eyeball. The authors identify that the peak SAR values are not in compliance with ICNIRP guidelines, but suggest since the associated temperature increase is small it would probably not support any adverse effect.
Findings		Effects
Status		Completed With Publication
Principal Investigator		Univ Hosp Utrecht, The Netherlands
Funding Agency		Private/Instit.
Country		NETHERLANDS
References		Flyckt, VM et al. Phys Med Biol, (2007) 52:2691-2701 Flyckt, VMM et al. Phys Med Biol. , (2006) 51:5007-5021 Van de Kamer, JB et al. Phys Med Biol, (2002) 47:1827-1835 Van Leeuwen, GM et al. Phys. Med. Biol., (1999) 44:2367-2379 Lagendijk, JJ Phys Med Biol, (1982) 27:1301-1311 Flyckt, VMM et al. Report., (2003) :- Flyckt, VMM et al. Report, (2003) :-
Comments		Similar results were obtained by Van Leeuwen (333), Wainwright (539), Wang (723), and Bernardi (763). Simple eye model without circulation [Bernardi et al, 1998; Takai & Fujiwara, 1998; Hirata et al, 2000] may produce higher temperature values per SAR input, although literature reports blood flow in retina and choroid may be 1020 times larger than in the brain [Follow & Neil, 1971; Alm & Bill, 1973].