Han et al. and 11 because chest radiographs performed at other insti- tutions showed positive findings of pneumoconiosis. Eighty-two patients were men, and three were women, and their age range was 25 57 (mean, 44) years. A history of exposure to dust fumes was available for 53 individuals, and the duration of this ranged from three to 30 (mean 15) years. In the study group of arc-welders, we had no pathologic proof of the existence of pneumoconiosis, and because of this, and because smoking may effect their CT findings, we included in this study, for comparative purposes, a group of smokers with a smoking history of 10 pack-years or more. It consisted of 43 men, 29 71 (mean, 55) years old, who between February and August 1995 underwent thin- section CT for the following reasons: evaluation of lung mass or nodule (n = 16), suspicion of active tuberculosis (n = 10), chronic obstructive lung disease (n = 10), pneumoth- orax (n = 3), hemoptysis (n = 2), suspicion of pulmonary metastasis (n = 1), and Loeffler’s syndrome (n = 1). Patients whose CT scans revealed diffuse parenchymal ab- normalities were not included in this group. The range of their smoking history was 10 50 (mean, 25) pack-years. Clinical findings and pulmonary function tests Among welders, documents regarding clinical findings were available for 53 individuals who answered a ques- tionnaire designed to elicit clinical information including the presence of cough, sputum production, dyspnea (classi- fied as one of four grades, according to the New York Heart Association), longevity of occupational exposure his- tory, and smoking history (pack-year). All 53 underwent pulmonary function tests which included measurement of forced vital capacity (FVC), and forced expiratory volume at 1 second (FEV1). FEV1/FVC was expressed as a per- centage. Imaging studies All subjects in both the welders’ (n = 85) and the smokers’ (n = 53) group underwent thin-section CT, performed using either a HiSpeed Advantage scanner (GE Medical Systems, Milwaukee, WI) (n = 98) or a Somatom Plus-S scanner (Siemens Medical Systems, Erlangen, Germany) (n = 40). Scans were obtained with 1-mm collimation at full inspira- tion and at five designated levels: 4-cm above the carina, at the carina, 4 cm and 8 cm below the carina, and at the di- aphragmatic dome. In no case was intravenous contrast medium administered. A high-spatial-resolution algorithm (bone algorithm) was used for image reconstruction, and im- ages were photographed with window widths and levels ap- propriate for visualization of the pulmonary parenchyma (window width, 1500 H; window level, -700H). 80 Imaging analysis Images of thin-section CT scans were interpreted retro- spectively by two radiologists experienced in thoracic imaging and decisions were reached by consensus. Findings were classified as either poorly-defined centrilobular mi- cronodules, branching linear structures, or ground-glass at- tenuation. Poorly-defined centrilobular micronodules were defined as those showing fuzzy centrilobular round opacity no greater than 7 mm in diameter, and 2 3 mm apart from the interlobular septae or pleural surface (5); branching lin- ear structures as poorly-defined X-or Y-shaped centrilobu- lar densities which did not taper peripherally as normal bronchovascular structures; ground-glass attenuation as poorly-defined opacity greater than 7mm in diameter which did not obliterate the parenchymal architecture. In each patient, the predominant pattern as well as its vertical and horizontal distribution was analyzed. Vertical distribu- tion referred to whether the findings were observed pre- dominantly in the upper lung zone (above the carina) or the lower (below the carina). Horizontal distribution re- ferred to whether they were noted predominantly in the peripheral lung zone (less than 3 cm from the parietal pleu- ra) or the central (more than 3 cm from the parietal pleura). Fig. 1. 46-year-old man whose smoking and exposure history were not available. Thin-section CT at the level of the origin of the right middle lobar bronchus shows poorly-defined centrilobular micronodules (ar- rows). Visual assessment indicated that the extent of abnormali- ties was 30 - 40%. Korean J Radiol 1(2), June 2000