<prompt> Which one of the following diagnostic techniques is most specific for pulmonary embolism?Pulmonary angiographyVentilation lung scanningPerfusion lung scanningAerial blood gas analysis  <response>: 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 