Quantitative CT in Chronic Obstructive Pulmonary Disease: Inspiratory and Expiratory Assessment

OBJECTIVE. The purpose of this study was to determine whether measurements of lung attenuation at inspiration and expiration obtained from 3D lung reconstructions reflect the severity of chronic obstructive pulmonary disease. SUBJECTS AND METHODS. Seventy-six patients with chronic obstructive pulmonary disease underwent MDCT with 3D postprocessing at full inspiration and full expiration. Inspiratory and expiratory mean lung density, percentage of lung volume with attenuation values less than -910 HU and -950 HU at inspiration and expiration, expiratory to inspiratory mean lung density ratio, and fifth and 15th percentiles of the lung attenuation distribution curve at inspiration and expiration were measured. RESULTS. When forced expiratory volume in the first second of expiration (FEV1) was 50% or greater than predicted value, mean lung density and lower attenuation volume measured from inspiratory MDCT scans correlated better with FEV1 and ratio of FEV1 to forced vital capacity (FVC) than did those from expiratory scans. When FEV1 was less than 50% of predicted value, mean lung density and lower attenuation volume measured from expiratory MDCT scans correlated better with FEV1 and ratio of residual volume to total lung capacity than did those values from inspiratory scans. Fifth percentile and 15th percentile of the lung attenuation distribution curve at both full inspiration and full expiration correlated well with FEV1/FVC and diffusing capacity of the lung for carbon monoxide as a percentage of predicted value but not well with FEV1 as a percentage of predicted value regardless of FEV1. CONCLUSION. Measurements of lung attenuation obtained at inspiration and visual score better reflect abnormal results of pulmonary function tests in patients with less severe chronic obstructive pulmonary disease than do measurements obtained at expiration. Measurements of lung attenuation obtained at expiration better reflect pulmonary function abnormalities in patients with severe chronic obstructive pulmonary disease.