This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
[{'content': 'Investigation of choice in bronchiectasis is \nSelect and explain. \nA. Bronchoscopy, B. MRI thorax, C. HRCT lung, D. Chest X-ray', 'role': 'user'}, {'content': 'Answer: C \nExplanation: HRCT chest is more specific for bronchiectasis and is the imaging modality of choice for confirming the diagnosis.CT findings include airway dilation(detected as parallel "tram tracks" or as the "signet-ring sign"-a cross sectional area of the airway with a diameter at least 1.5 times that of the adjacent vessel),lack of bronchial tapering(including the presence of tubular structures within 1 cm from the pleural surface.),bronchial wall thickening in dilated airways,inspissated secretions (eg.,the " tree-in-bud" pattern ),or cysts emanating from the bronchial wall(especially pronounced in cystic bronchiectasis.) Reference:Harrison\'s medicine-18th edition,page no:2143.', 'role': 'assistant'}]