Chen et al. normality of central airways underwent spiral thin-section CT scanning with 3-D SSD imaging. In 41 of the 126, all chest radiographs and routine thick-section CT, thin-sec- tion spiral CT, MPR and 3-D SSD images were available. This retrospective study was based on these 41 cases. Fifteen of the patients were men and 26 were women, and they were aged between 21 and 71 (mean, 45) years. The final diagnoses were endobronchial tuberculosis (n = 18), bronchogenic carcinoma (n = 10), congenital abnor- mality (n = 3), post-operative stenosis (n = 2), and others (n = 8), conditions which were confirmed either histopathologically or clinically. In 33 cases, chest radiographs were obtained using a film-screen system and the high-voltage technique, and in eight, by means of computed radiography. For all spiral CT examinations, a Somatom Plus-S or Plus 4 scanner (Siemens Medical Systems, Erlangen, Germany) was used, while for routine CT (RCT) scans, the spiral technique (8- 10-mm collimation, pitch of 1) was employed. Scan para- meters for thin-section spiral CT (TCT) scans were 2 3- mm collimation, 4-mm table feed, and 1 2-mm recon- struction interval. Intravenous contrast medium was used in all cases involving RCT scanning, and in 25 involving TCT. For this modality, the length of the z-axis was 9 20 cm, and all such scans were obtained during a single breath hold. Axial images were obtained at both mediastinal win- dow setting (window width 300 400 HU, window level 0 40 HU) and lung window setting (window width 1300 1500 HU, window level -650 to -750HU). The TCT data were used to create both MPR and SSD images on the CT workstation. In all cases, coronal and sagittal MPR images were obtained along the long axis of the trachea (Fig. 1A), and in selected cases, oblique or curved reformatted images (Fig. 1B) were added. In all cas- es, MPR images were obtained at mediastinal window set- ting (window width 300 400 HU, window level 0 60 HU), and in selected cases at lung window setting (window width 1400 1800 HU, window level -470 to -600 HU). SSD images were obtained using double threshold voxel selection (5); the lower threshold was -700 HU, and the upper was between -200 and - 250 HU. In 25 cases, SSD images were edited to remove unnecessary lung parenchy- mal structures, using the cutting facility of the 3-D package (Fig. 2). In the remaining 16 cases (including all five of left upper lobar lesions), images were preprocessed with slice by slice editing to remove unwanted volumetric image data (Fig. 3). Three-dimensional images were obtained at a win- dow width of 300 HU and window level of 900 1100 HU. In each patient, chest radiographs RCT, TCT, 2-D MPR, and SSD images were retrospectively evaluated by two chest radiologists (Q.C., J-G.I), who reached a consensus. Images obtained by means of various techniques were ana- lyzed for detectability, localization, extent, and characteri- zation of the lesion, information on its relationship with adjacent structures, and overall information. Each feature A B Fig. 1. Bronchogenic carcinoma in a 66-year-old man. A. Coronal MPR image shows apparent total obstruction of the left main bronchus by a polypoid soft tissue lesion (arrow). B. Curved reformatted image along the axis of the left upper lobe shows focal wall thickening of the left main bronchus (arrow). 136 Korean J Radiol 1(3), September 2000