The characteristics of emphysema and pulmonary perfusion derived from spectral CT in smokers

Tobacco smoking may cause pulmonary perfusion abnormality. Assessment of the lung perfusion characteristics is very significant to timely treatment and prevent disease progression in smokers. The purpose was to investigate the value of iodine maps from spectral dual-layer detector computed tomography (DLCT) in assessing lung perfusion changes in smokers.

Nineteen smokers and 29 non-smokers who underwent dual-phase contrast enhanced scans on a spectral DLCT were retrospectively collected. Emphysema on non-contrast images and perfusion defect (PD) on iodine maps were scored visually at bilateral lung fields of three anatomic levels (on the slice of the aortic arch, the carina, and the aperture of the inferior pulmonary veins). The scores were calculated based on the ratio of the abnormality occupied in the pulmonary field of each slice as described below: point 0, no abnormality; point 1, 0%< abnormality scope ≤25%; points 2, 25%< abnormality scope ≤50%; points 3, 50%< abnormality scope ≤75%; points 4, abnormality scope >75%. The sum of scores for each patient was calculated. The iodine density (ID) of PD and thoracic aorta were measured respectively (ID_defect, ID_{thoracic aorta}), then calculating the ratio as the normalized ID (nID). Emphysema index (EI) was defined as the volume percentage of the lung attenuation below -950 Hounsfield units. The percentage of forced expiratory volume in 1 second (FEV₁) to the predicted value (FEV₁%) and the ratio of FEV₁ to forced vital capacity (FVC) were recorded. The differences of the emphysema and PD visual scores, ID_defect, nID, EI were analyzed by analysis of variance between smokers and non-smokers. Correlations between emphysema, PD and FEV₁%, FEV₁/FVC were evaluated by Spearman correlation analysis.

The PD visual scores on ID images were significantly higher in smokers compared with that in non-smokers (P=0.014), while no significantly difference was found for emphysema visual scores (P=0.402). Both ID_defect and nID were significantly lower in smokers compared with non-smokers (P=0.003; P=0.029), while no significantly difference was found for EI (P=0.061). Besides, PD visual scores were negatively correlated with FEV₁% (r=-0.61, P=0.025) and FEV₁/FVC (r=-0.62, P=0.024) for smokers.

Compared with emphysema, the iodine map derived from spectral DLCT showed higher sensitivity for the evaluation of the pulmonary abnormalities of smokers.