Clinical diagnosis of acute pulmonary embolism. When should a V/Q scan be ordered?

@article{Dalen1991ClinicalDO,
  title={Clinical diagnosis of acute pulmonary embolism. When should a V/Q scan be ordered?},
  author={James E. Dalen},
  journal={Chest},
  year={1991},
  volume={100 5},
  pages={1185-6}
}