Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Moderate to severe left lower lobe atelectasis is improving from prior collapse . Lung volumes are unchanged . The cardiomediastinal silhouette and hilar contours are stable . There is no large pleural effusion or pneumothorax . There is no concerning focal opacity .
    OUTPUT:
    
Improving left lower lobe atelectasis .