Statistical analysis
All statistical analyses were performed with R software (version 3.5.1; Receiver-operating characteristic (ROC) curves were applied to assess the predictive ability of the models in distinguishing benign from malignant SPSNs, and accuracy, sensitivity, specificity, and the area under the curve (AUC) were calculated respectively. The DeLong test was used to compare the AUC between different models or different datasets. Calibration curves were plotted and the Hosmer-Lemeshow test was used to assess the fitness of the models. Decision curves were used to compare the clinical usefulness of models.