2.2 Chest CT protocols
Non-enhanced chest CT were performed in either of the four CT units (SOMATOM Definition AS128, Siemens; uCT 780, United Imaging; Optima 660, GE; SOMATOM Definition AS+, Siemens) with the slice thickness of 10 mm. The scanning range covered from lung apex to diaphragm on axial plane taken under free breathing with the patients in supine position. If necessary, 0·50ml/kg body mass of 10% chloral hydrate was taken orally before the examination. Thin-section CT images were reconstructed with 0·625 mm collimation with a standard algorithm and then sent to the Picture Archiving and Communication System (PACS) for analyzing.