Fig. 3

a Axial CT scan (lung window) was done for metastatic workup of the patient, showed a peripheral left upper lobe ground-glass pulmonary nodule, b CT histogram for the segmented nodule. GGN showed type α (sharp peak at low CT value), mean density: − 423.2 HU, maximum density: − 255 HU, minimum density: − 830 HU, STD: 146.7, and skewness was negative. Kurtosis was positive with peak frequency 24%. c Note the changes on follow-up after 2 years as follows: histogram of the segmented GGN showed type β, mean density: − 434.1 HU, maximum density: − 348 HU, minimum density: − 714 HU, STD: 78.6, skewness is negative, and kurtosis is positive with peak frequency 36%