A 45-year-old woman presents with sudden onset pleuritic chest pain and shortness of breath 2 days after returning from a long-haul flight. She has a swollen right calf. Her oxygen saturation is 93% on room air and she is haemodynamically stable. Chest X-ray is normal. Wells score suggests a high probability of pulmonary embolism. What is the most appropriate next investigation to confirm the diagnosis?