An MRI method is disclosed for the geometrical characterisation of pulmonary airways on the basis of a first tridimensional image of at least one bronchus of a bronchial tree and includes: acquiring a first MRI image, an MRI sequence being synchronised with a respiratory frequency; filtering the first image; segmenting a portion of the filtered image including the contours of the bronchial tree and its inner volumetric portion; estimating at least one plane of cut of a bronchus; generating at least one image slice of a bronchus; estimating, for each image slice, an area contained within the bronchial wall and/or a bronchial wall thickness.