The Intra-observer Variability Of Volumetric Measurement And Percentage Volume Change Of Pulmonary Nodules:Comparison Of Two-dimensional And Three-dimensional Method

Background and ObjectiveSoftware oriented three-dimensional (3D) volumetric measurement of pulmonary nodules(PN) has been feasible in the follow-up of indeterminate pulmonary nodules, however, its value need a further validation. The purpose of this study is to retrospectively analyze the chest CT data of patients with pulmonary nodules to compare the intra-observer variability of3D and two-dimensional (2D) volumetric measurement. Then we analysis the impacts of volume measurement difference on pulmonary nodule percentage volume change(PVC) of follow-up patients and repeatability of each volume measurement method.Materials and MethodsEighty-six PNs in chest CT scans of79subjects were retrospectively analyzed. One radiologist measured the nodules twice with a7days interval using2D and3D methods respectively. The 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. The3D measurements were acquired with semi-automated software with manual adjustment on unsatisfied nodule segmentation. The definition of satisfaction is the nodule segmentation region just complete winding the lung nodule, otherwise is not.Logistic regression analysis was performed to evaluate the effect of nodule location and morphology on3D nodule segmentation. There were71nodules in3D segmentation with satisfaction, then comparing the volume change overtime, the PVC was defined as the difference between follow-up and baseline measuring volumes divided by the baseline volume.ANOVA and correlation test were used to evaluate the difference among three methods. Bland-Altman method was applied to quantify the intra-observer variability. We us25%as nodule growth standards of PVC to determine each nodule with different volume measurement method whether the result is positive, we use Kappa test to show the consistency of the three measurements.Results1.3D method achieved satisfied segmentation for81.4%nodules. The irregular and juxtavacular nodules have significantly high odds rations (OR) of unsatisfied segmentation as4.0,4.5, respectively.2. The volume measured by three method was significantly different(F=6.5, P=0.012),while the repeated measurements did not led to significant difference (F=1.813, P=0.182)3. The Spearman correlation efficient between3D volume and2D volume with sphere and ellipsoid model was0.97,0.88.4. The95%limits of agreement of RD between two repeated measurements were-14%～11.6%,-37.7%～39.9%and-39.8%～45.8%for3D,2D with elliptical model and spherical model, respectively.5. The the PVC measured by three method was no significant difference in the71nodules with satisfied segmentation (F=0.647, P=0.527). At the same time, the repeated measurements did not led to significant difference (F=0.687, P=0.410).The spearman correlation efficient showed that two repeated measurements of3D volume measurement had the highest correlation (0.948, P<0.001).6.3D volume measurement own the highest repeatability, The95%limits of agreement of AD between two repeated measurements were-15.98%～13.3%.7. The Kappa test show good consistency ratio between3D and2D sphere model volume measurements, but the consistency did not reach a high level(below0.55), Kappa value were of0.354(P<0.001) for3D and2D with sphere model volume,0.541(P<0.001)for3D and2D with ellipsoid model.Conclusion1. The3D volume measurement of pulmonary nodules is more repeatable than2D volume measurement. Unsatisfied segmentation can occurred on a small number of nodules, especially for irregular and juxtavascular nodules. For these nodules, the measurement of3D diameters is recommended.2. Three volume measurements can used to show the PVC of nodule between follow-up and baseline, but3D seems better for good repeatability. Nodule’s location and morphology can add3D PVC measurement variability, especially in follow-up examinations, we need to carefully observe the segmentation of the nodule, then give a good inspection and verification of the PVC of the same nodule.