Huda Walter, Lieberman Kristin A, Chang Jack, Roskopf Marsha L
Department of Radiology, SUNY Upstate Medical University, Syracuse, New York 13210, USA.
Med Phys. 2004 Mar;31(3):588-94. doi: 10.1118/1.1646232.
We investigated how patient age, size and composition, together with the choice of x-ray technique factors, affect radiation doses in head computed tomography (CT) examinations. Head size dimensions, cross-sectional areas, and mean Hounsfield unit (HU) values were obtained from head CT images of 127 patients. For radiation dosimetry purposes patients were modeled as uniform cylinders of water. Dose computations were performed for 18 x 7 mm sections, scanned at a constant 340 mAs, for x-ray tube voltages ranging from 80 to 140 kV. Values of mean section dose, energy imparted, and effective dose were computed for patients ranging from the newborn to adults. There was a rapid growth of head size over the first two years, followed by a more modest increase of head size until the age of 18 or so. Newborns have a mean HU value of about 50 that monotonically increases with age over the first two decades of life. Average adult A-P and lateral dimensions were 186+/-8 mm and 147+/-8 mm, respectively, with an average HU value of 209+/-40. An infant head was found to be equivalent to a water cylinder with a radius of approximately 60 mm, whereas an adult head had an equivalent radius 50% greater. Adult males head dimensions are about 5% larger than for females, and their average x-ray attenuation is approximately 20 HU greater. For adult examinations performed at 120 kV, typical values were 32 mGy for the mean section dose, 105 mJ for the total energy imparted, and 0.64 mSv for the effective dose. Increasing the x-ray tube voltage from 80 to 140 kV increases patient doses by about a factor of 5. For the same technique factors, mean section doses in infants are 35% higher than in adults. Energy imparted for adults is 50% higher than for infants, but infant effective doses are four times higher than for adults. CT doses need to take into account patient age, head size, and composition as well as the selected x-ray technique factors.
我们研究了患者的年龄、体型和组成，以及X射线技术因素的选择如何影响头部计算机断层扫描（CT）检查中的辐射剂量。从127例患者的头部CT图像中获取头部尺寸、横截面积和平均亨氏单位（HU）值。为了进行辐射剂量测定，将患者建模为均匀的水圆柱体。对18×7mm的切片进行剂量计算，在340mAs恒定条件下扫描，X射线管电压范围为80至140kV。计算了从新生儿到成年人的患者的平均切片剂量、传递能量和有效剂量值。头围在出生后的头两年迅速增长，随后直到18岁左右头围增长较为缓慢。新生儿的平均HU值约为50，在生命的前二十年中随年龄单调增加。成人的平均前后径和横径分别为186±8mm和147±8mm，平均HU值为209±40。发现婴儿头部相当于半径约为60mm的水圆柱体，而成人头部的等效半径大50%。成年男性的头部尺寸比女性大约5%，其平均X射线衰减约大20HU。对于在120kV下进行的成人检查，平均切片剂量的典型值为32mGy，传递的总能量为105mJ，有效剂量为0.64mSv。将X射线管电压从80kV增加到140kV会使患者剂量增加约5倍。对于相同的技术因素，婴儿的平均切片剂量比成人高35%。成人传递的能量比婴儿高50%，但婴儿的有效剂量是成人的四倍。CT剂量需要考虑患者的年龄、头部尺寸和组成以及所选的X射线技术因素。
