Quantitative computed tomographic indexes in diffuse interstitial lung disease: Correlation with physiologic tests and computed tomography visual scores

PURPOSE: To assess the correlation among quantitative indexes of computed tomography (CT), spirometric pulmonary function tests (PFTs), and visual scores (VSs) of CT in patients with diffuse interstitial lung disease (DILD) and to prove the estimated value of CT quantification for the prediction of the possibility of pulmonary function impairment. METHODS AND MATERIALS: A total of 157 patients (male to female ratio, 96:61; mean age, 63 ± 11 years) with DILD were enrolled in this study. All patients underwent volume thin-section CT in the supine position at full inspiration. During the same period, 23 people (male to female ratio, 10:13; mean age, 55 ± 13 years) with no history of DILD and with normal PFTs and CT findings were used as a control group. Quantitative indexes were obtained using a commercial CAD system (Brilliance Workspace v3.0; Philips Medical Systems). Quantitative indexes included total lung volume (TLV), mean lung attenuation, variation of lung attenuation, emphysema volume (<-950 Hounsfield units [HU]), functioning lung volume (-700 HU > pixel > -950 HU), and interstitial lung disease volume (>-700 HU). Visual scores were measured semiquantitatively and included the overall extent of pulmonary parenchymal abnormality as well as the extent of consolidation, ground glass opacity, reticulation, and honeycomb opacities. Quantitative indexes were correlated with PFT and VSs using the Pearson correlation test. RESULTS: Quantitative indexes, PFT results, and VSs differed significantly between the DILD group and the control group, except for emphysematous parameters (P < 0.05).Pulmonary function test results showed significant correlation with quantitative indexes in the DILD group. Functioning lung volume showed positive correlation with forced vital capacity and forced expiratory volume in 1 second (r = 0.80 and 0.73, P < 0.001). Total lung capacity showed positive correlation with TLV (r = 0.83, P < 0.001).Visual scores were correlated with the ratio of a specific volume to TLV (indicated as ®). Interstitial lung disease volume® showed positive correlation (r = 0.53, P < 0.001), and FLV® showed a negative correlation with the overall extent of ILD (r = -0.52, P < 0.001). variation of lung attenuation showed a positive correlation with honeycombing extent (r = 0.37, P < 0.001), and mean lung attenuation showed a positive correlation with reticulation extent (r = 0.42, P < 0.001). CONCLUSIONS: Quantitative indexes measured by a commercial workstation showed good correlation not only with the extent of DILD estimated by visual inspection but also with PFT results. Quantitative indexes can be used as an objective tool for quantitative evaluation of disease extent and for follow-up of the progression or improvement of a DILD.