Inclusion Criteria:  age > 18 years and BMI ≤ 30 kg/m2 fewer than four pulmonary nodules without calcification solid nodules (SNs) with a diameter of 4~15 mm and subsolid nodules (SSNs) with a diameter of 5~20 mm and containing part-solid nodules (PSNs) and ground-glass nodules (GGNs) (the diameter is the mean of the longest diameter and perpendicular diameter of a nodule) acceptable diagnostic image quality of LDCT.  Exclusion Criteria:  None