Images in a 34-year-old female patient show severe smoking-associated small airway disease with patchy ground-glass opacities and mosaic pattern. The images were generated with spectral postprocessing on a coronal plane at (A) inspiration (warped for voxelwise matching with expiration), (B) ventilation, (C) perfusion, (D) expiration, (E) CT angiography, and (F) late contrast enhancement. Quantitative parameters include whole lung or lobar volume, and inspiratory (A) and expiratory (D) attenuation and functional parameters such as ventilation (B), perfusion (C), and late contrast enhancement (F). They are described using descriptive statistics or histogram analysis. Corresponding functional maps show inhomogeneous ventilation with lobular air-trapping in the lower lobes and matched perfusion inhomogeneities. CT angiography (E) and late contrast enhancement (F) images show no abnormal findings. Credit: Radiological Society of North America

Representative coronal preoperative ventilation-perfusion CT (A–C) and postoperative ventilation-perfusion CT (D–F) images obtained after pulmonary endarterectomy in a 64-year-old female patient with chronic thromboembolic pulmonary hypertension. Circles show pathology. (A) CT angiographic image obtained before surgery shows a wall-adherent thrombus in the central right pulmonary artery extending into the upper lobe artery. (C) Perfusion image shows a corresponding lobar defect in the right upper lobe; region of interest (circle) placed in right upper lobe with a normalized iodine uptake of 4%. (B) Ventilation is homogeneous (region of interest in right upper lobe, 0.46) and preserved at normal level, representing a ventilation/perfusion mismatch. After surgical removal of the thrombus (circle in D), the perfusion in the right upper lobe increased (circle in F; from 4% to 13%), and ventilation remained stable within normal range and comparable before (B) and after (E) surgery. Credit: Radiological Society of North America

Representative coronal images obtained in an 82-year-old male patient with persisting shortness of breath 1 month after COVID-19 infection. Circles indicate pathology. The virtual noncontrast-enhanced images at (A) inspiration, (B) warped inspiration, and (C) expiration show areas of ground-glass opacifications in the right upper lobe, as well as emphysema in the left lung. The perfusion image (E) and the late enhancement image (F) show corresponding high values with ground-glass opacifications in the affected areas of the lung. (D) The ventilation image is heterogeneous, with areas of low to no ventilation in areas of emphysema, normal ventilation in healthy areas, and increased ventilation (ie, collapse) in the ground-glass opacifications. Exemplary measurements with region of interest in the right upper lobe are as follows: ventilation, 0.61; perfusion, 18% of vessel contrast; and late enhancement, 79% of vessel contrast. Credit: Radiological Society of North America