Statistical analysis
All statistical analyses were carried out using SPSS for Windows 15.0 (SPSS Inc., Chicago, IL, USA). Continuous variables with normal distribution were expressed as mean ± standard deviation (SD), and categorical variables were expressed as number and percentage. Sensitivity and specificity values, accuracy, positive and negative predictive values were analyzed by the contingency table and calculated for CDUS CTA as the gold standard method. Bland-Altman plot was generated to evaluate agreement between two measurements of sac diameter (CDUS and CTA) by constructing limits of agreement. These limits are calculated by using the mean and standard deviation of the differences between two measurements. At least 95% of paired measurements were expected to lie within ± 2 SD of the mean difference. Linear regression analysis was conducted to assess proportional bias. Type-I error of 0.05 was set as statistically significant.