Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Examination is technically limited due to suboptimal patient positioning . Retrocardiac opacity is either atelectasis or aspiration . The lungs appear clear . Cardiomediastinal contour is within normal limits . No pleural effusion or pneumothorax .
    OUTPUT:
    
Retrocardiac atelectasis or aspiration . Followup radiographs are recommended .