Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A portable frontal chest radiograph demonstrates low lung volumes . Bilateral opacities are consistent with mild pulmonary edema . A retrocardiac opacity may be secondary to atelectasis / edema , but a superimposed infectious process can not be excluded . There may be a trace left pleural effusion . No pneumothorax is identified . The visualized upper abdomen is unremarkable .
    OUTPUT:
    
Low lung volumes , with mild pulmonary edema . A retrocardiac opacity may be due to a combination of atelectasis and edema , but superimposed pneumonia can not be excluded .