Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral radiographs of the chest demonstrate clear lungs with minimal retrocardiac opacification which is similar to the prior radiograph . No definite evidence of pneumonia . The cardiac and mediastinal contours are normal . No pleural abnormality is detected .
    OUTPUT:
    
Unchanged retrocardiac opacification since ___ , with no definite evidence of pneumonia .