Which one of the following diagnostic techniques is most specific for pulmonary embolism?

Pulmonary angiography is the standard test for the diagnosis of pulmonary embolism. Algorithms have been developed for patients with appropriate clinical data and high-probability results on ventilation and perfusion lung scanning; in such cases, this combined technique has almost the diagnostic accuracy of pulmonary angiography. Abnormal results on aerial blood gas analysis and chest x-ray are too nonspecific to be helpful. When ventilation and perfusion scanning, aerial blood gas analysis, or both produce normal results and the alveolar-aerial P02 is normal, pulmonary embolism is extremely unlikely