Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to the prior radiograph , there has been interval decrease in lung volumes , which accentuates the cardiomediastinal contours and bronchovascular structures . Small right sided pleural effusion is unchanged since the prior study . Right lung base opacity may represent infection or atelectasis , and is similar since the prior study . No pneumothorax . Hilar and mediastinal contours are otherwise within normal limits . No bony abnormality is seen .
    OUTPUT:
    
Right lower lung field opacity may be infection or atelectasis . Small right pleural effusion is unchanged since ___ , given lower lung volumes .