Background and objective Sotfware oriented three-dimensional (3D) volumetric measurement of pul-monary nodules has been feasible in the follow-up of indeterminate pulmonary nodules, however, its value need a further vali-dation. hTe purpose of this study is to retrospectively analyze the chest CT data of patients with pulmonary nodules to compare the intra-observer variability of 3D and two-dimensional (2D) volumetric measurement. Methods Eighty-six pulmonary nod-ules in chest CT scans of 79 subjects were retrospectively analyzed. One radiologist measured the nodules twice with a 7 days interval using 2D and 3D methods respectively. hTe maximal diameter (X), the perpendicular diameter (Y) on maximal cross sectional area of the nodule and the caudo-cranial diameter (Z) were measured and the volume was calculated by two models:spherical and elliptical model. hTe 3D measurements were acquired with semi-automated sotfware with manual adjustment on unsatisifed nodule segmentation. Logistic regression analysis was performed to evaluate the effect of nodule location and mor-phology on 3D nodule segmentation. ANOVA and correlation test were used to evaluate the difference among three methods. Bland-Altman method was applied to quantify the intra-observer variability. Results Sotfware achieved satisifed segmentation for 86.4%nodules. hTe irregular and juxtavacular nodules have signiifcantly high odds rations (OR) of unsatisifed segmenta-tion as 4.0, 4.5, respectively. hTe volume measured by three method was signiifcantly different (F=6.5, P=0.012), while the repeated measurements did not led to signiifcant difference (F=1.813, P=0.182). hTe Spearman correlation effcient between 3D volume and 2D volume with sphere and ellipsoid model was 0.97, 0.88. hTe 95%limits of agreement of RD between two repeated measurements were-14%-11.6%,-37.7%-39.9%and-39.8%-45.8%for 3D, 2D with elliptical model and spherical model, respectively. Conclusion hTe 3D volume measurement of pulmonary nodules is more repeatable than 2D volume measurement. Unsatisifed segmentation can occurred on a small number of nodules, especially for irregular and juxtavascular nodules. For these nodules, the measurement of 3D diameters is recommended.%背景与目的未定性肺结节的随访需要精确测量结节体积确定其生长特性。结节体积的三维测量可通过软件实现并应用于临床，其在临床实践中的价值尚需进一步验证。本研究回顾性分析肺结节患者胸部CT平扫影像资料，比较三维体积测量与传统二维肺结节测量的观察者内的重复性。方法对2011年1月-2012年12月间在天津医科大学总医院行未定性肺结节CT随访研究的79例患者共86个结节的CT影像资料进行分析。由一名放射科医师对肺结节间隔1周行重复二维及三维体积测量。二维（two dimension,2D）测量结节轴位最大横截面上的最大径（X）、相应垂直径（Y）及结节的头尾径（Z），分别根据球体及椭球体模型体积计算公式计算结节体积。三维（three dimension,3D）测量通过计算机肺结节半自动体积测量软件进行，对结节自动体积分割效果不佳者行人工调整。应用Logistic回归分析评估结节的形态及位置对肺结节三维体积分割结果的影响。应用方差分析、相关分析评估3种体积测量方法的差异、Bland-Altman法评估3种方法的重复性。重复性定义为两次测量之间的相对差值（rela-tive difference, RD）。结果86例结节两次三维软件体积测量中，软件分割效果满意结节占81.4%。Logistic回归分析提示边缘不规则结节及与血管相连结节软件分割不满意的比率明显增高，似然比（odds ratios, OR）分别为4.0、4.5。方差分析显示经二维测量与三维软件体积测量所得体积具有明显差异（F=6.5, P=0.012），同一方法两次重复测量结节体积间无统计学差异（F=1.813, P=0.182）。软件测量体积与椭球体模型体积相关性较球体模型高（相关系数分别为0.974、0.882）。3D软件体积测量重复性最佳，RD 95%一致性区间为-14%-11.6%，其次为2D椭球体模型体积(-37.7%-39.9%)，最后为2D球体模型（-44.63%-46.4%）。结论肺结节软件三维体积测量较二维测量具有更高的重复性。对软件体积分割不满意结节，包括不规则形态及与血管相连结节，我们建议测量结节的三维径线并应用椭球体模型计算体积。
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