Lung density in HU was respectively measured at the level of aortic arch, the carina area and the level of inferior pulmonary vein stem. The mean lung density (MLD) at various dosage and collimation was calculated and a statistical analysis was made.

• 分别在主动脉弓、气管隆突、下肺静脉干平面测量肺密度 (HU) ,计算不同剂量、层厚平均肺密度并进行统计学分析。