HRCT features of interstitial pulmonary fibrosis. A. Normal aspect of the lung. B. Mild. C. Moderate. D. Severe. A'. US examination of healthy interlobular septa at lung surface level. Note as the pleura is a linear and regular hyperechoic band (arrow). B'-D'. US examinations showing different scores of fibrotic pulmonary involvement: B'. Mild. C'. Moderate. D'. Severe.