辐射剂量和成像系统对测量肺磨玻璃密度结节CT体积准确性的影响

Impact of radiation dose and imaging system on the volumetric measurement accuracy of ground-glass opacity nodules

目的评价辐射剂量和成像系统对测量磨玻璃密度(GGO)结节体积准确性的影响。方法应用MDCT和宝石能谱CT(HDCT)在7种不同噪声指数(NI)下对含有14个相同大小GGO结节的胸部体模进行扫描,采用0.625mm层厚、骨算法重建获得图像,使用Lung VCAR软件测量GGO结节体积。根据CT机器测定的剂量指数(CTDI)计算每次扫描的有效辐射剂量(ED)。应用方差分析和配对t检验对所测结节体积进行分析。结果 14个结节标准体积均为981.25mm3,7种不同NI扫描时MDCT和HDCT检测的结节体积间差异有统计学意义(P均<0.05)。随着NI增加,MDCT和HDCT测得结节体积的误差率逐渐增大,而ED逐渐下降。相同NI下,宝石能谱CT的ED较MDCT降低34.48%～50.00%,差异有统计学意义。结论相同NI下,HDCT测量GGO体积的准确性优于MDCT。在NI=15时,HDCT的ED较低,测量GGO结节体积的误差较小。

Objective To evaluate the impact of the radiation dose and imaging system on the volumetric measurement accuracy of ground-glass opacity（GGO） nodules detection.Methods MDCT and HDCT scan were performed on chest phantom containing 14 identical artificial GGO nodules with 7 different noise indexes（NI=10,15,20,25,30,35,40）.All data were reconstructed with slice thickness of 0.625 mm and bone algorithm for reconstruction.Nodule volumes were measured using Lung VCAR software.Effective dose（ED） was calculated on the basis of dose length product and volumetric CT dose index.Analysis of variance and paired t test were used to analyze the measured nodule volumes.Results The standard volume of all artificial GGO nodules was 981.25 mm3.There were statistically significant differences between the groups of 7 different NI for the error of volumetric measurement of GGO nodules by MDCT and HDCT（all P0.05）.With the increase of NI,nodule volume error enlarged gradually measured with MDCT and HDCT,while ED gradually decreased.ED for the chest scan on HDCT was significantly lower than that on MDCT with 34.48%—50.00% in the same NI,and statistical difference was found between them.Conclusion In the same NI,the volume measurement accuracy of HDCT is superior to volume CT.When NI of 15,HDCT scan can not only ensure low ED,but also reduce the error of measurement on nodule volume.