Fig. 2

The phase of maximal inhalation was visually identified from respiratory motion, and oblique axial/coronal images parallel to the right MPA were created at that phase (a (1, 2) red line). In the oblique sagittal image, we determined the cross-section located exactly in the middle of the right MPA; from the trunk of the pulmonary artery—the right MPA bifurcation to the right MPA—right superior pulmonary artery bifurcation (a (3)). We manually traced the right MPA as finely as possible in this cross-section (b). This was followed by auto-tracing to the remaining phases, e.g., inhalation phase (c (1)), intermediate phase (c (2)), and exhalation phase (c (3)). The cross-sectional area (mm²) of the right MPA in each phase was then output. MPA, Main pulmonary artery