64层螺旋CT自动管电流调节技术在婴幼儿胸部低剂量CT扫描中应用的可行性研究

摘要

目的 探讨应用64层螺旋CT(MSCT),采用适宜噪声指数的Z轴自动管电流调节技术获得稳定的婴幼儿胸部CT扫描图像,并降低射线剂量的可行性研究.方法 选取100例根据临床需要行64层MSCT胸部扫描的3岁以下婴幼儿患儿,按年龄和体重用随机数字表法分为2组,每组各50例.对照组(中位年龄1.7岁)采用固定管电流扫描技术:1岁以下120 mA,≥1岁者150 mA;研究组(中位年龄1.4岁)采用z轴自动管电流调节扫描技术:1岁以下预设噪声指数为8,≥1岁为9,毫安设置范围为10～250 mA,其余扫描参数条件2组一致.记录2组CT剂最指数(CTDIvol)值.2名医师独立对图像质量采用5分制进行评估,＞13分被认为符合临床诊断要求.采用Kappa方法评价不同观察者评定结果间的一致性.结果 对照组的平均客观噪声和CTDIvol分别为(4.78 4±0.58)和(6.68±0.62)mGy,研究组的平均客观噪声和CTDIvol分别是(7.84±0.66)和(2.34±0.71)mGy;研究组和对照组的平均管电流分为(41.6 4±11.6)和(99.2±7.7)mAs.研究组的平均CTDIvol较对照组下降了 65%.研究组和对照组平均图像质量评分分别为(3.46±0.40)和(4.65±0.46)分,所用图像均获得了满意的临床诊断要求,2名医师的评估结果获得了中等一致性(Kappa值分别为0.474和0.536).结论 64层MSCT自动管电流调节技术应用于婴幼儿胸部扫描时可以在降低射线剂量的基础卜获得稳定的图像质量,噪声指数设定在8或9较为适宜.%Objective To assess the feasibility of using an automatic tube current modulation (ATCM)method to obtmn consistent image quality with reduced radiation dose for young children undergoing chest scans with a set of 64-slice spiral CT.Methods Fifry young children underwent chest scans on a GE 64-slice VCT with automatic tube current modulation.The noise index(NI)for this study group was set to 8 or 9 based on the proposed reference for pediatric chest imaging in our hospital.We compared image quality and radiation dose for the study group with the age-matched control group of 50 young children acquired with standard protocol of fixed-mAs(120 and 150 mAs for under 1 and above 1 year old,respectively).The volume CT dose index(CTDIvol)values were recorded for beth groups.Two experienced pediatric radiologists assessed image quality on a 5-point scale with 5 being the best.Scores greater than or equal to 3 were considered clinically acceptable.The degree of interobserver concordance was determined by Kappa statistics.Results The average objective image noise and CTDIvol for control group was(4.78±0.58)and(6.68±0.62)mGy,respectively.For the study group the mean value of objective mAs wag(41.6±11.6)(20-79 mAs)with mean CTDIvol of(2.34 4±0.71)mGy,and the use of ATCM produced mean noise of(7.84±0.66).The average CTDIvol with the use of NI of 8-9 was about 65% lower than that with the fixed mAs setting.The mean image quality score for the study group and control group was(3.46±0.40)and(4.65±0.46)respectively.All studies had acceptable image quality,and there was good inter-observer agreement in diagnostic acceptability(Kappa=0.474 and 0.536).Conclusion The automatic tube current modulation method could be used to obtain consistent image qualityfor young children undergoing 64-slice MSCT chest scans.With proper noise level setting(NI=8 or 9),one may obtmn clinically acceptable images with much reduced radiation dose.