## 3 Results  
Segmentation and computerized analysis with ImageJ software were successfully performed for all PSNs. The quantitative CT features calculated from the baseline CT images are listed in Table 2.  
The time interval between the baseline and last follow-up CT scan ranged from 99 to 2224 days (median, 699 days; IQR, 263-1232 days). The LMD calculated from the last follow-up CT images ranged from 12.6 to 129.7 mg/mm (median, 42.4 mg/mm; IQR, 25.2-71.8 mg/mm). The LMD-DT calculated by matching the baseline and last follow-up CT images ranged from 343 to 25520 days (median, 1422 days; IQR, 1005-9018 days). A statistically significant correlation was observed between the LMD-DT and the quantitative CT features, including area, perimeter, mean Feret diameter, LMD, circularity and solidity (\(p\leq 0.031\)) (Table 2). The CR obtained from the Bland-Altman analysis was 11.3% (Figure 3). Therefore, only an increase in the LMD greater than 11.3% was considered significant growth. A significant increase in the LMD that exceeded the CR (i.e., \(>\)11.3%) between the baseline and last follow-up CT scan was detected in 33/50 (66%) PSNs. In this group of growing PSNs, the LMD increased from 12.3 to 235.2% (median, 55.4%; IQR, 30.9-89.9%) after a median time interval of 740 days (IQR, 340-1241 days) (Figure 4). The LMD-DT ranged from 343 to 5824 days (median, 1111 days; \begin{table}
\begin{tabular}{c c c c} \hline \hline
**CT Feature** & **Value** & **Spearman’s Rho \({}^{*}\)** & \(p\) Value \({}^{*}\)** \\ \hline Area (mm\({}^{2}\)) & 67 (40.5–86.8) & \(-\)0.306 & 0.031 \\ Perimeter (mm) & 36.9 (27.6–46.4) & \(-\)0.449 & 0.001 \\ Mean Feret diameter (mm) & 11 (8.3–13.2) & \(-\)0.365 & 0.009 \\ Mean attenuation (HU) & \(-\)497.3 (\(-\)563.5—449) & \(-\)0.069 & 0.633 \\ Median attenuation (HU) & \(-\)534.5 (\(-\)605—478) & \(-\)0.019 & 0.897 \\ Modal attenuation (HU) & \(-\)703 (\(-\)758—596) & \(-\)0.029 & 0.842 \\ Standard deviation (HU) & 226 (202.2–248.6) & \(-\)0.241 & 0.092 \\ Skewness & 0.67 (0.46–0.91) & \(-\)0.003 & 0.983 \\ Kurtosis & \(-\)0.17 (\(-\)0.61–0.53) & 0.124 & 0.390 \\ LMD (mg/mm) & 31.4 (20–43.5) & \(-\)0.326 & 0.021 \\ Circularity & 0.64 (0.52–0.75) & 0.519 & \(<\)0.001 \\ Solidity & 0.81 (0.74–0.87) & 0.457 & \(<\)0.001 \\ \hline \hline \end{tabular} \({}^{*}\)Spearman rank correlation between the quantitative features and the LMD doubling time. Data are presented as the median (interquartile range). LMD, linear mass density.  
\end{table} 
Table 2: Quantitative CT features calculated from the baseline CT images of all part-solid nodules. IQR, 828-1520 days) with the minimum time interval needed to detect growth ranging from 40 to 880 days (median, 143 days; IQR, 101-217 days). In this growing group, 12/33 (36.4%) PSNs were surgically removed with a histological diagnosis of pulmonary adenocarcinoma (nine minimally invasive adenocarcinomas graded as pT1 mi and three invasive adenocarcinomas graded as pT1a). In 3/33 (9.1%) growing PSNs, stereotactic radiotherapy or radiofrequency ablation was performed due to the clinical status and comorbidities of the patients. In the nongrowing group, which comprised 17/50 (34%) PSNs, the computerized analysis did not detect a significant change in the LMD after a median time interval of 349 days (IQR, 193-1026 days). The quantitative CT features that were significantly different between the groups of growing and nongrowing PSNs were area, perimeter, mean Feret diameter, standard deviation of CT attenuation, LMD, circularity and solidity (\(p\leq 0.013\)) (Table 3). The relationships between PSN growth and independent variables (patient age, sex, smoking and oncologic history, emphysema status and PSN lobe location) were listed in Table 4.  
Only oncologic history was significantly associated with PSN growth (\(p\) = 0.004). The relationship of nodule growth with sex (\(p\) = 0.062) and smoking history (\(p\) = 0.061) was just outside the limit of significance.