Chest CT scan
CT scans were performed on a 64-slice spiral CTs (Philips, iCT, Netherlands) .The scan parameters are 120 kV (tube voltage) , 210 mA ( tube current ) , FOV 500 mmx500 mm, matrix 512x512, pitch 0.975, rotation time 0.35-0.5 s/circle, scanning layer thickness 5 mm, reconstruction layer thickness 1 mm.