Investigation of choice in bronchiectasis is

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.