<prompt> Gold standard for diagnosis of pulmonary embolismChest X-rayPulmonary angiographyVentilation perfusion scintiscanCT  <response>: CT-pulmonary angiography CTPA is the gold standard test for pulmonary embolism.It has the advantages of visualising the distribution extent of the emboli,or highlighting an alternative diagnosis,such as,consolidation,pneumothorax, or aoic dissection.A definitive diagnosis of PE depends on visualisation of an intraluminal filling defect in more than one projection.Secondary signs of PE include abrupt occlusion cut-off of vessels,segmental oligemia or avascularity,a prolonged aerial phase with slow filling, and touous,tapering peripheral vessels. Reference:Harrisons medicine-18th edition,page no:2174. 