The initial chest CT data of 56 patients from Chongqing Three Gorges Central Hospital were obtained by using a 16-slice spiral CT scanner (Emotion 16 VC20B, Siemens Healthcare GmbH) with the following scanning protocol: a tube voltage of 120 kV, smart mA tube current modulation, a slice thickness of 1.5 mm, and a detector width of 1.5 mm.