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Silicosis in 76 Men: Qualitative and Quantitative CT Evaluation—Clinical-Radiologic Correlation Study¹

¹ From the School of Professional and Continuing Education, Dept of Radiology (G.C.O., P.L.K., H.N., I.W.T.H., F.L.C.), Depts of Diagnostic Radiology and Medicine (K.W.T.T., M.S.M.I., W.K.L., M.C.Y.), and Div of Traditional Chinese Medicine (T.F.C.), Univ of Hong Kong, Queen Mary Hosp, F/4, Block K, Pokfulam, Hong Kong SAR, China; and Hong Kong Wanchai Chest Clinic, Dept of Health (C.M.T.). Received May 15, 2002; revision requested Jul 26; final revision received Nov 22; accepted Jan 14, 2003. Supported by a CRCG grant from the Univ of Hong Kong and by the Hong Kong Pneumoconiosis Fund Board. Address correspondence to G.C.O. (e-mail: cgcooi@hkucc.hku.hk).

PURPOSE: To use qualitative and quantitative computed tomography (CT) to test the hypothesis that impaired lung function with silicosis is due to progressive massive fibrosis (PMF) and associated emphysema.

MATERIALS AND METHODS: Seventy-six men with silicosis underwent volumetric and thin-section CT of the thorax. Lung function, Borg scale dyspnea grade, silica exposure duration, and cigarette consumption were determined. Nodular profusion (NP) at chest radiography was graded according to the International Labor Organization radiographic classification system; NP and PMF at CT were visually graded by using five-point (ie, grades 0–4) and four-point (grades 0–3) scales, respectively. Emphysema and NP, which together are defined as the NP index, were quantified by using attenuation threshold values of less than -950 HU and greater than -100 HU, respectively. Mean lung attenuation was also determined. Relationships among the CT, chest radiographic, and clinical parameters were analyzed by using Spearman correlation.

RESULTS: NP at chest radiography correlated (r > 0.50) with all CT parameters of nodularity. CT PMF had the highest correlation with emphysema (r = 0.58, P < .001). NP at chest radiography and all CT parameters were inversely related to lung function. At multiple regression analysis, PMF and emphysema index (both at CT) were significant determinants of forced expiratory volume in 1 second (FEV₁) (P = .006 and .03, respectively) and FEV₁ to forced vital capacity (FVC) ratio (P = .007 and .02, respectively). Mean lung attenuation remained related to FVC (P = .03), diffusing capacity of lung for carbon monoxide (P = .04), and Borg scale grade (P = .01). Cigarette consumption and silica exposure duration had no independent effects on lung function.

CONCLUSION: Qualitative and quantitative CT parameters can be used as indirect measures of functional impairment in silicosis. PMF and emphysema are independently related to airflow obstruction, whereas mean lung attenuation is related to clinical dyspnea and reduced lung volume.

© RSNA, 2003

Index terms: Emphysema, pulmonary, 60.751 • Lung, CT, 60.12111, 60.12118 • Lung, fibrosis, 60.6113 • Lung, function • Silicosis, 60.771

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