Quantitative computed tomography in chronic obstructive pulmonary disease.

TLDR: Quantitative computed tomography is being increasingly used to quantify the features of chronic obstructive pulmonary disease, specifically emphysema, air trapping, and airway abnormality.

Abstract: Quantitative CT is increasingly used to quantify the features of COPD, specifically emphysema, air trapping, and airway abnormality. For quantification of emphysema, the density mask technique is most widely used, with threshold on the order of-950 HU, but percentile cutoff may be less sensitive to volume changes. Sources of variation include depth of inspiration, scanner make and model, technical parameters, and cigarette smoking. On expiratory CT, air trapping may be quantified by evaluating the % of lung volume less than a given threshold (e.g. -856 HU), by comparing lung volumes and attenuation on expiration and inspiration, or more recently by co-registering inspiratory and expiratory CT scans. These indices all correlate well with the severity of physiologic airway obstruction. By constructing a three-dimensional model of the airway from volumetric CT, it is possible to measure dimensions (external and internal diameters, and airway wall thickness) of segmental and subsegmental airways orthogonal to their long axes. Measurement of airway parameters correlates with severity of airflow obstruction and with history of COPD exacerbation.