A 75 - year - old lady with severe chronic obstructive pulmonary disease (COPD) presents with acute breathlessness. The chest X - ray shows there is no focal consolidation. She is afebrile, but D - dimers are markedly elevated. Which of the following is best investigation to diagnose this condition ?
MRI Ventilation - perfusion (V/Q) scan High resolution CT thorax CT pulmonary angiography