Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single AP upright portable chest radiograph demonstrates no focal opacity convincing for pneumonia . Relative to prior study dated ___ , the cardiomediastinal and hilar contours are stable in appearance with slightly unfolded calcified aorta . Lung volumes are low with mild atelectasis . There is no large pleural effusion or pneumothorax . Osseous structures are unremarkable .
    OUTPUT:
    
No acute intrathoracic abnormality .