Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Since the prior radiograph , there has been no significant change . Lung volumes are again low , probably due to poor inspiration . Retrocardiac opacity is similar in appearance to prior on the frontal but improved onthe lateral likely from better inspiratory effort . There is no pneumothorax or pleural effusion . The cardiomediastinal silhouette is unchanged and mildly enlarged . The osseous structures are unremarkable .
    OUTPUT:
    
No significant change since the prior radiograph . Retrocardiac opacity likely due to atelectasis ; however , infectious process can not be completely excluded .