Background: In the screening of pulmonary subsolid nodules (SSNs), it is crucial to compare the quantitative parameters under consistent computed tomography (CT) acquisition conditions, including the same degree of lung inflation. When non-end-inspiratory chest CT scan is performed due to poor breath holding, there is a risk of inaccurate measurement of quantitative parameters and erroneous assessment of pulmonary nodule growth. This study aims to investigate the effect of respiratory phase on three-dimensional (3D) quantitative parameters of SSNs, and to further explore the impact of respiratory phase change on the judgment of SSNs growth during the follow-up of low-dose CT (LDCT) screening.
Methods: There were 255 pulmonary SSNs retrospectively found in 230 subjects who received low-dose paired inspiratory and expiratory chest CT screening. Quantitative parameters of lung and SSNs on paired inspiratory and expiratory CT were obtained. The change ratio of expiratory to inspiratory parameters was calculated and labeled as parameter(E-I)/I. Quantitative parameters were compared between inspiratory and expiratory CT. The difference of the change ratio of different quantitative parameters was also compared. The change ratio of quantitative parameters of SSNs was compared between different density types, sizes and locations. The 255 nodules were divided into two groups (the changed and unchanged group) according to the growth criteria. The quantitative parameters and the change ratio of quantitative parameters were compared between the two groups. The significant factors were included in the multivariate logistic regression analysis.
Results: There were statistical differences in all quantitative parameters of lung nodules between the inspiratory CT and the expiratory CT (all P<0.05). The change ratio of long axis diameter of nodules (7.14%) was the smallest, and the change ratio of volume of nodules (20.21%) was the largest. Significant differences were found in the change ratio of most quantitative parameters between part-solid nodules (PSNs) and pure ground-glass nodules (pGGNs). There was no statistical difference in the change ratio of all nodules' parameters between the ≤10 mm group and the >10 mm group (all P>0.05). Nodule density(E-I)/I in lower lobes was greater than that in upper lobes (P<0.001). Significant differences were found in the change ratio of lung volume, the change ratio of long axis diameter and density of nodules, and all quantitative parameters of nodules on inspiratory CT between the changed group and the unchanged group (all P<0.05). Multivariate logistic regression analysis showed that the lung density, long axis diameter, short axis diameter, surface area and density of nodules on inspiratory CT were independent indicators for predicting whether SSNs change with respiratory phase.
Conclusions: Respiratory phase had the greatest effect on the volume of pulmonary SSNs and the least effect on the long axis diameter. During follow-up, LDCT scan in different respiratory phases may interfere with the judgment of the growth of pulmonary SSNs.
