Fig. 3.

Example deformed lungs from NLM-Montgomery dataset [59]. Green contour is expected lung anatomy delineated by a radiologist [36]. Red contour is the algorithm’s decision as lung boundary. a, b The algorithm could not detect the lung boundary correctly due to opacity caused by fluid in the lung space. c The left diaphragm is elevated, and there is a large air-distended colon loop below the lung which is incorrectly combined with the lobe into a single region by the algorithm. d Detected lung boundary includes the air cavity below left lung