MRCP2-4274

A 68-year-old man with a history of ischaemic heart disease, left ventricular hypertrophy, hypertension, and type 2 diabetes presents to the Acute Medical Assessment Unit with progressive shortness of breath. He has been a heavy smoker for the past 50 years. His blood tests show a slightly elevated white blood cell count and C-reactive protein level, but are otherwise unremarkable. A chest x-ray reveals bilateral pleural effusions, cardiomyopathy, and pleural plaques. The patient responds well to intravenous diuresis, but a significant residual pleural effusion remains on the right side. What further investigation should be performed for this patient?