32 year old Kalpana presented with complaints of difficulty in breathing, chest pain, and increased rate of breathing. Pulmonary thromboembolism is suspected. Investigation useful in acute pulmonary thromboembolism is:

The ventilation-perfusion scan (V/Q) has been the most common diagnostic test for suspected pulmonary embolism. 99Tc-radiolabeled albumin is injected intravenously into the pulmonary capillary bed followed by inhalation of a radioactive gas to assess ventilation. A diagnosis of pulmonary embolism is based on the pattern of ventilatory and perfusion defects with PE causing large segmental decrease in perfusion with preserved ventilation. Major disadvantages of this test are the limitations posed by the presence of comorbid lung disease and the test's lack of sensitivity for small clots. Ref: Nana-Sinkam P. (2003). Chapter 19. Pulmonary Thromboembolism. In M.E. Hanley, C.H. Welsh (Eds), CURRENT Diagnosis & Treatment in Pulmonary Medicine.