乳幼児の電気定数を考慮した1-6GHz全身平均SARの推定

摘要

With much concern about health effects of children for radio-wave exposure, nowadays, analytical studies on whole-body averaged specific absorption rates (WBA-SARs) in anatomical based child models have actively been conducted. For the WBA-SAR calculation, however, dielectric constants of adult tissues have so far been employed. Since children have higher conductivity than adults do, there is a speculation that their WBA-SARs must be larger compared to the case for adults. In this study, we derived electric tissue constants of infants by using a formula for age-dependence of dielectric properties based on total body water (TBW), which was proposed by Wang, et al. in 2006, and thereby calculated their WBA-SARs with the FDTD method to compare the results with those used for adult tissue constants. As a result, we found that the WBA-SARs calculated for infant tissue constants unexpectedly become smaller than those done for adult constants, which are reduced by 1 % for 5 year child model and 3 % for 9 month infant model, respectively.%電波の子供に対する人体影響の関心が高まり，数値モデルに対するSAR(Specinc Absorption Rate)計算が盛んにおこなわれてはいるが，組織電気定数は成人のそれが用いられてきた．子供は発育途上にあるため，組織導電率は概して高く，それ故に全身平均SARは成人のそれよりも上昇するのではないかとの懸念がある．本研究では，2006年にWangらが提案した人体組織電気定数の体内総水分量に基づく年齢依存式から乳幼児の電気定数を算出し，乳幼児に対する全身平均SARのFDTD解析結果を，成人の電気定数を用いた場合との対比で示した．その結果，体内総水分量を考慮した電気定数に対する全身平均SARの計算結果は，意外にも成人の電気定数を用いた場合よりも小さく，その減少の程度は5歳児で1％,9ケ月幼児では3％と年齢が低いほど顕著になることがわかった．