High-resolution CT (HRCT) scanning and dynamic CT techniques have significantly improved our ability to image morphologic abnormalities associated with chronic airflow obstruction. Abnormalities visible on HRCT include emphysema, lung cysts, and large airways abnormalities, such as bronchiectasis, which are accurately assessed using this technique. Also visible are small airways abnormalities, such as bronchiolar dilation and filling of bronchioles with mucus or fluid. Perfusion abnormalities resulting from abnormal lung ventilation result in regional differences in lung attenuation, so-called mosaic perfusion. Expiratory HRCT scans or dynamic scans during expiration can show areas of air trapping.