Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP and lateral views of the chest are compared to previous exams from ___ . Linear opacities identified at the lung bases , most suggestive of atelectasis given their configuration . There is also subtle residual retrocardiac opacity which has improved since ___ . Elsewhere , the lungs are clear . Cardiomediastinal silhouette is normal . Osseous and soft tissue structures are unremarkable .
    OUTPUT:
    
Subtle residual retrocardiac opacity , which has improved since exam from ___ , which could represent resolving infection ; however , repeat examination is recommended in four to six weeks to document complete resolution of this finding . Bibasilar atelectasis .