Visual and Automated CT Measurements of Lung Volume Loss in Idiopathic Pulmonary Fibrosis.

OBJECTIVE. The purpose of this study is to establish the relationship between CT markers of lung volume and pulmonary function test (PFT) parameters of lung volume in idiopathic pulmonary fibrosis (IPF). MATERIALS AND METHODS. The relationships between PFT-derived parameters of lung volume (forced vital capacity [FVC] and total lung capacity [TLC]) and both CT-derived automated lung volume and manually derived surrogate measurements of lung volume on CT were evaluated in 273 patients (212 men and 61 women; median age, 67 years) with a multidisciplinary diagnosis of IPF. All patients underwent unenhanced volumetric high-resolution CT of the thorax. Automated lung volume was extracted using commercially available software. Three manual CT surrogate measurements of lung volume previously tested in the setting of radiation-induced lung fibrosis were evaluated by two raters. These measurements were lung height, aortosternal distance, and oblique fissure retraction distance. Fibrosis extent on CT was scored by two observers. Correlation coefficients and multivariable regression analyses were performed to assess the relationship between CT measurements and percentage of predicted FVC (hereafter referred to as "percentage FVC") and TLC. Interobserver agreement for CT markers was evaluated on the basis of the intraclass correlation coefficient. RESULTS. There was a strong correlation between CT-derived automated lung volume and TLC (rP = 0.92; p < 0.0005). There was excellent interobserver agreement for all manual CT measurements (intraclass correlation coefficient, 0.82-0.96). There were significant correlations between manual CT measurements and percentage FVC. Lung height had the strongest relationship with percentage FVC (rP = 0.44; p < 0.0005). In multivariable analysis, the CT measurements were independent determinants of lung volumes, after adjustment for fibrosis and emphysema (R2 = 0.48; p < 0.0005 and p < 0.003, respectively). Lung height had the most significant impact on the fit against lung volumes. CONCLUSION. Automated and manual CT measurements of lung volume are significantly related to PFT-derived parameters of lung volume, independent of fibrosis and emphysema.