Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear unchanged . Within the limitations of technique , the lungs appear clear aside from questionable vague increased posterior density suggesting minor atelectasis or crowding of bronchovascular structures . Evaluation is somewhat limited , however , by low lung volumes .
    OUTPUT:
    
No definite evidence of acute cardiopulmonary disease . Low lung volumes .