Image interpretation and data analysis

Three-dimensional volume rendering lung images were created using a commercially available, user-friendly imaging software program (Ziostation 2^®; Ziosoft, Inc., Tokyo, Japan). Threshold limits of −600 to −1,024 HU were applied to segment the entire lungs and to exclude soft tissues surrounding the lungs and the large vessels, atelectasis, fibrosis, and tumors within the lung. The volume of a lung that was segmented by a certain threshold limit can be readily obtained with the imaging software program. We called the volume of the entire lungs (−600 to −1,024 HU), the total lung volume (TLV). The lungs were divided into two areas: low-attenuation areas, representing emphysematous lung tissue (<−950 HU); and normal-attenuation areas (−600 to −950 HU), representing normal lung fields. We calculated the entire volume and the low-attenuation volume (LAV) for each lobe and the entire lungs.