Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: As compared to chest radiograph from same day , substantial improved aeration of the left lung post bronchoscopy . Persistent retrocardiac opacity likely reflects ongoing left lower lobe atelectasis . No pulmonary edema . Likely small left effusion . No pneumothorax .
    OUTPUT:
    
Substantial improved aeration of the left lung with persistent left lower lobe atelectasis .