Remy-Jardin et al.10 did not detect GGO in CT scans of 51 non-smokers. A study of Vikgren et al.22 found GGO to be a part of smoking-induced disease. They showed that the progression in the extent of GGO was seen among smokers in a 6-year interval, but that the occurrence of GGO was higher among ex-smokers than among never-smokers. Septal lines were found in both never- and current smokers.