Background: Solitary pulmonary nodule (SPN) evaluation based on analyses of combined wash-in (WI) and washout (WO) values obtained by helical dynamic CT (HDCT) scanning is useful for malignant SPN characterization, because this method has higher specificity and accuracy than that based on analyses of WI values only. However, increased specificity results in reduced sensitivity and the missing of malignant SPNs. Thus, the purpose of this study was to seek the most effective method for SPN characterization during HDCT scanning.
Methods: After obtaining unenhanced CT scans, dynamic CT scanning was performed using a helical technique (images were obtained at 30, 60, 90, and 120 s, and at 5 and 15 min after the initiation of IV contrast administration) in 486 patients with a solid or partly solid SPN. Diagnostic efficacies were compared for three approaches involving considerations of WI values (in Housfield units [HU]) only, both WI and WO HU values, and WI HU values and morphologic characteristics.
Results: Considering WI values only (≥ 25 HU), sensitivity, specificity, and accuracy for malignancy were 98% (233 of 237 nodules), 46% (114 of 249 nodules), and 71% (347 of 486 nodules), respectively. Using both a WI value of ≥ 25 HU and a WO value of 5 to 36 HU, the corresponding values were 89% (212 of 237 nodules), 79% (197 of 249 nodules), and 84% (409 of 486 nodules), respectively; for a WI value of ≥ 25 HU and a malignant morphology, the corresponding values were 92% (219 of 237 nodules), 79% (197 of 249 nodules), and 86% (416 of 486 nodules), respectively (these values were significantly different between the WI-only group and the other two groups; p = 0.001).
Conclusions: The efficacy of SPN evaluation based on analyses of WI values plus morphologic features during HDCT scanning appears to be equivalent to that based on analyses of WI plus WO values, thus obviating the need for WO scans, which saves time and reduces radiation exposure of the patient.