OBJECTIVE. The objectives of our study were to evaluate the in vivo reproducibility of automated volume calculations of small lung nodules with both low-dose and standard-dose CT and to assess whether repeatability within each technique varies according to the diam�eter, site, or morphology of the nodule or to percentage of emphysema.
SUBJECTS AND METHODS. Sixty-six subjects with 83 solid pulmonary nodules between 5 and 10 mm in diameter were enrolled in this prospective study. Four consecu�tive MDCT data sets, two low dose and two standard dose, were obtained for each nodule on separate breath-holds during the same session. The volume of each nodule was calculated by automated software. Repeatability was evaluated by Bland-Altmans approach and the coef�ficient of repeatability. Associations of the percentage of volume variation between two mea�surements with nodule diameter, emphysema percentage, nodule site, and nodule morphology were assessed by Spearmans correlation coefficient and the Kruskal-Wallis test. A p value of
RESULTS. The range of variation of the volumes of pulmonary nodules between two subsequent measurements was -38% � 60% for low-dose CT and -27% � 40% for standard-dose CT. No significant statistical association was found between variation in volume mea�surements and nodule site, nodule diameter, nodule morphology, or emphysema percentage by semiautomated calculation of lung density.
CONCLUSION. Automated volume calculations of small pulmonary nodules can sig�nificantly differ between two subsequent breath-holds with both low-dose and standard-dose CT techniques; in clinical practice we recommend that a volume variation of greater than 30% for nodules between 5 and 10 mm should be confirmed by follow-up CT to be sure that a nodule is actually growing.