Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable semi-upright radiograph of the chest demonstrates low lung volumes . The cardiac silhouette is unremarkable and stable since the prior examination . The mild engorgement of the pulmonary vasculature in comparison to the most recent study . Left basilar opacity may represent atelectasis versus pneumonia .
    OUTPUT:
    
Left basilar opacity may represent atelectasis versus pneumonia .