米国のBrennerらは，小児のcomputed tomography(CT)の検査件数が10年前に比べて飛躍的に増加しており，それに伴い被ばくのリスクも増加していると警鐘を鳴らしている.米国でのCT検査件数のうち小児が占める割合は1989年頃には全体の4％程度であったが2002年には10％に増加しており，このうち33％が10歳以下，17％が5歳以下である.放射線感受性が高く，成長に伴い体格が変化する小児では，放射線被ばくに対する特別な対策が必要である.2001年に米国食品医薬品局(Food and Drug Administration: FDA)から，体重に合わせた小児CTに対する被ばく低減が提唱され，DonnellyらのシングルヘリカルCTのデータがその指標として採用された.更にDonnellyらは，2003年にmulti-detector-row CT(MDCT)を用いた体重別撮影法を提案している.%We aimed to apply the pediatric abdominal CT protocol of Donnelly et al. in the United States to the pediatric abdominal CT-AEC.Examining CT images of 100 children, we found that the sectional area of the hepatic portal region (y) was strongly correlated with the body weight (x) as follows: y=7.14x + 84.39 (correlation coefficient=0.9574). We scanned an elliptical cone phantom that simulates the human body using a pediatric abdominal CT scanning method of Donnelly et al. in, and measured SD values. We further scanned the same phantom under the settings for adult CT-AEC scan and obtained the relationship between the sectional areas (y) and the SD values. Using these results, we obtained the following preset noise factors for CT-AEC at each body weight range: 6.90 at 4.5-8.9 kg, 8.40 at 9.0-17.9 kg, 8.68 at 18.0-26.9 kg, 9.89 at 27.0-35.9 kg, 12.22 at 36.0-45.0 kg, 13.52 at 45.1-70.0 kg, 15.29 at more than 70 kg. From the relation between age, weight and the distance of liver and tuber ischiadicum of 500 children, we obtained the CTDI_(vol) values and DLP values under the scanning protocol of Donnelly et al. Almost all of DRL from these values turned out to be smaller than the DRL data of IAEA and various countries. Thus, by setting the maximum current values of CT-AEC to be the Donnelly et al.'s age-wise current values,and using our weight-wise noise factors, we think we can perform pediatric abdominal CT-AEC scans that are consistent with the same radiation safety and the image quality as those proposed by Donnelly et al.
展开▼
