Figure 2.

Measurement of the depth ratio in a 3D-CTBA image. The center of the bronchial opening of the pulmonary lobe to which the lung nodule belongs is marked as point O, and the center of the pulmonary nodule is labeled as point A. Extend the line connecting points O and A towards the visceral pleura. The extension that intersects the rib-facing visceral pleura or the well-developed interlobar pleural membrane is marked as point B. The depth of the pulmonary nodule from the hilum is approximately represented by the ratio BA/BO. Nodules with a depth ratio of 0–33.3%, 33.4–66.6%, and 66.7–100% are defined as outer region, middle region, and inner region nodules, respectively. CTBA, computed tomography bronchography and angiography.