A 75 year old man who had been on bed rest for the past 14 days, complains of breathlessness and chest pain. The chest X-ray is normal. The next investigation should be:

This patient might be having pulmonary embolism, for which Pulmonary aeriography is diagnostic. Actually Chest CT with contrast has viually replaced invasive pulmonary angiography as a diagnostic test. Lung scanning has become a second-line diagnostic test for PE, used mostly for patients who cannot tolerate intravenous contrast. Echocardiography is not a reliable diagnostic imaging tool for acute PE because most patients with PE have normal echocardiograms. Ref: Harrisons principles of internal medicine, 18th edition, chapter 262.