Clinical usefulness of helical computed tomography in evaluating chronic obstructive pulmonary diseases

To assess the usefulness of helical computed tomography (CT) in evaluating pathophysiological abnormalities in chronic obstructive pulmonary disease, we compared the results of helical CT with those of pulmonary function tests in 46 subjects with pulmonary emphysema. We obtained 3-D images of emphysematous lung tissue by choosing voxels with values less than -930 HU because the mean CT score in 10 normal subjects was -869 ± 29 HU. For each patient the total lung volume (TLV) was computed from the 3-D image of the entire lung with CT score less than -600 HU, and the volume of emphysematous lung tissue (ELV) as computed from the lung with CT score less than -930 HU. TLV measured on inspiration correlated significantly with TLC (r = 0.601, p < 0.001), and TLV measured on expiration correlated significantly with RV (r = 0.836, p<0.0001). The difference between inspiratory TLV and expiratory TLV correlated significantly with VC (r=0.781, p<0.001). ELV both on inspiration and on expiration correlated significantly with FEV₁/FVC (p<0.001) and with RV (p<0.01, p<0.001, respectively. These results suggest that the volume data obtained by helical CT reflect functional abnormalities of the lung. In addition to volume data, the distribution of abnormal lung tissue is easily assessed by helical CT. We conclude that helical CT is useful in evaluating pathophysiological abnormalities in chronic obstructive pulmonary disease.