2.2. CT and PFTs
Before CT scanning, all patients received instructed training to achieve full-inspiratory and end expiratory breath hold. CT scans during full inspiration and end expiration were obtained craniocaudally in the supine position throughout the entire thorax without intravenous contrast material. All CT examinations were performed using a helical CT scanner (Somatom Force, Siemens Medical Systems, Erlangen, Germany) using a 250–350 mm field of view, a 512×512 reconstruction matrix, 80~100 kVp, effective mAs (CARE Dose 4D), and a tube rotation time of 0.25 ms. For lung parenchymal analysis, images were reconstructed using the following parameters: 1 mm thickness, no interval, and Br36 kernel. CT attenuation measurements were taken using the CT Pulmo 3D application in a 3D solution program (Syngovia; Siemens). The application calculated the attenuation coefficient for each voxel in the lung and a frequency distribution of voxels with specific attenuation numbers.
All PFTs were performed with a Vmax instrument (Sensor Medics, VIASYS Healthcare, Yorba Linda, CA) according to guidelines from the American Thoracic Society and European Respiratory Society.