The "solid" component within subsolid nodules: imaging definition, display, and correlation with invasiveness of lung adenocarcinoma, a comparison of CT histograms and subjective evaluation

ObjectiveTo validate three proposed definitions of the solid component of subsolid nodules, as compared to CT histograms and the use of different window settings, for discriminating the invasiveness of adenocarcinomas in a manner that facilitates routine clinical assessment.MethodsWe retrospectively analyzed 328 pathologically confirmed lung adenocarcinomas, manifesting as subsolid nodules. Three-dimensional CT histograms were generated by setting 11 CT attenuation intervals from -400 to 50HU, at 50HU intervals, and the voxel percentage within each CT attenuation interval was generated automatically. Three definitions of the solid component were proposed, and 10 medium window settings were set to evaluate the solid component. The diagnostic performance of the three definitions for identifying invasive adenocarcinoma was compared with that of CT histogram analysis and subjective evaluation with medium window settings.ResultsA parallel diagnosis using five intervals with the largest AUC (AUC0.797) demonstrated good differential diagnostic performance, with 78% sensitivity and 73.7% specificity. Definition 2 (visibility in the mediastinum window) yielded higher accuracy (75.6%) than the other two definitions (p<0.01). A medium window setting of -50 WL/2 WW gave a larger AUC than the other nine medium window settings as well as definition 2, with 82.5% specificity and 88.5% PPV, which was higher than those of parallel diagnosis with CT histogram and definition 2.ConclusionUsing -50 WL/2 WW is the optimum approach for evaluating the solid component and discriminating invasiveness, superior to using 3D CT histograms and definition 2, and convenient in routine clinical assessment.Key Points center dot -50 WL/2 WW gave a larger AUC than definition 2.center dot The specificity of -50 WL/2 WW was higher than CT histograms.center dot -50 WL/2 WW offers the best evaluation of the solid component.