Fig. 2

Male patient, 45 years old, chronic heavy smoker. a–c HRCT images with subtle bilateral diffuse emphysematous changes. d–f After applying density mask, image segmentation. g Lung density histogram. Although pulmonary function tests were normal, there were bilateral emphysematous changes with both lower lobes more emphysematous than both upper lobes as regarding the low-density index that of both lower lobes was 18.2%while that of both upper lobes was 15.7%, and the left lung is more emphysematous than the right lung. Findings revealed more pronounced bilateral diffuse emphysematous changes, more pronounced at the left lower lobe (left lower lobe low-density index 19.9%), and to a lesser degree left upper lobe(left upper lobe low-density index 18.5%)