Journal of Hong Kong College of Radiologists

Volume 4 Number 1, 2001

Lung volume measurement in chronic obstructive pulmonary disease: Application of helical computed tomography

GC Ooi1, KWT Tsang2, TF Cheung3, WK Lam2, CYM Fok1, FML Ng4, FL Chan4, H Ngan1
1Department of Diagnostic Radiology and 2Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong
3Division of Traditional Chinese Medicine, SPACE, The University of Hong Kong
4Department of Radiology, Queen Mary Hospital, Hong Kong

Objectives: To evaluate correlation of static lung volumes obtained by helical computed tomography (CT) with standard physiological methods, and to assess the relationship between CT-derived emphysema volume (EV) with lung function parameters in patients with chronic obstructive pulmonary disease (COPD). Methods: Twenty-five patients with suspected COPD were recruited. Lung function tests, high resolution CT (HRCT) and inspiratory and expiratory helical CT were performed. An attenuation threshold of -400 and -1024 HU was applied to inspiratory and expiratory helical data sets to obtain three dimensional (3D)-CT TLC and 3D-CT RV respectively. A threshold of -910 and -1024HU was applied to inspiratory helical data set to obtain 3D-CT EV. HRCT and CT axial images were evaluated for visual emphysema. Pearson's correlation analysis was used to evaluate relationship between helical CT and physiological lung volumes, and between 3D-CT EV and lung function and clinical parameters. Two patients who refused lung function tests were excluded. Results: Of 23 patients [3 women, mean age SD (68.9 8.7 years)], three had no quantifiable emphysema. There was a correlation between CT-derived and physiologically measured TLC and RV (r=0.61, p=0.002; r=0.71, p=0.0003 respectively). Overall CT-EV correlated with RV (r=0.50, p<0.05), while CT-EV more than 100mL (n=10) showed a relationship with DLCO (r=-0.63, p<0.05). CT-EV less than 100mL (n=10), correlated with FEV1 and FEV1/FVC (r=-0.64, p<0.05; r=-0.65, p<0.05 respectively). Smoking did not exert any effect on either lung function or emphysema volume. Conclusions: Helical CT is a feasible method of quantifying static lung and emphysema volumes, and provides an indirect measure of lung function in COPD patients. (J HK Coll Radiol 2001;1:53-58)

Key words : Computed Tomography, Emphysema, Helical, Lung volume

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