A 29-year-old woman presents to the Acute Medical Unit with sudden onset shortness of breath and pleuritic chest pain. She returned from a 12-hour flight 5 days ago. Observations: HR 115 bpm, RR 24/min, SpO2 94% on room air, Temp 37.1°C, BP 125/80 mmHg. Chest examination is clear, and CXR is normal. Her Wells score for Pulmonary Embolism (PE) is calculated as 5 (Clinical signs of DVT=0, PE most likely diagnosis=3, HR>100=1.5, Immobilisation/surgery=0, Previous PE/DVT=0, Haemoptysis=0, Malignancy=0. Adjusted for flight >4h + Recent Travel ~ 1.5 + 3 + 1.5= 6). Let's use score 6. According to NICE NG158, what is the most appropriate next diagnostic step?