Lung volume segmentation steps.

a) Original image, b) 3D image of the main trachea and bronchus tree, c) binary image in which the main trachea and bronchus tree were filled, d) initial segmented lung regions and local enlarged view of the fused position, e) fused lung region separated into two distinct regions and local enlarged view of indentation location, f) boundary repairing, g) 3D image of lung volume with artifacts and other tissue and h) 3D image of lung after removing other structures.