Quantification of Emphysema in Chronic Obstructive Pulmonary Disease by Volumetric Computed Tomography of Lung

Abstract

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease with small airway inflammation and emphysema. Emphysema is permanent enlargement of air spaces distal to terminal bronchioles accompanied by destruction of alveolar walls. These morphological changes can be studied on quantitative computed tomography (CT). Thirty-four patients diagnosed to have COPD as per Global Initiative for Chronic Obstructive Lung Disease guidelines underwent chest CT using full inspiration with low dose radiation protocol. Pulmo-CT software was used to analyse the scans. The primary aim was to quantify emphysema and emphysema clusters and secondary aim was to assess correlation between percentage emphysema and lung function. Their mean [standard deviation (SD)] age was 66.4 (7.0) years; 11 (32.4%) were current smokers (median pack years 45.5). Their mean (SD) forced expiratory volume in the first second (FEV1%) was 55.6 (17.6), mean (SD) %emphysema was 26.8 (11.1), mean (SD) lung density was -848.35 (29.5) Hounsfield units (HU), median (interquartile range) %cluster class 4 emphysema was 22.4 (13.5-32.6). There was no significant difference in %low attenuation volume (%LAV) in current and exsmokers (p=0.4); across various severity grades of COPD (p=0.15). Further, no significant correlation was observed between %emphysema and post-bronchodilator FEV1%. Volumetric CT can detect and quantify emphysema. Majority of emphysema clusters in COPD are >25mm. The %emphysema does not correlate to the severity of the disease. Quantitative CT is a good objective method to study emphysema and can be used to phenotype COPD radiologically.