This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
A 55 year old man who has been on bed rest for the past 10 days, complain of breathlessness and chest pain. The chest X-ray is normal. The next step in the investigation should be – 
Select and explain. 
A. Lung ventilation – perfusion scan, B. Pulmonary arteriography, C. Pulmonary venous wedge angiography, D. Echocardiography
A: Lung ventilation – perfusion scan
Answer: A: Lung ventilation – perfusion scan 
Explanation: This patient has a high clinical likelihood of pulmonary embolism because clinical assessment score is more than 4:-


Signs & symptoms of PE (Breathlessness & chest pain) → score 3.0
Immobilization (bed rest) > 3 days → score 1.5


So, the total score is 4.5. Therefore, imaging test should be done. CT contrast is the imaging test of choice.