1. A method for producing an image of the lung of a subject with a magnetic resonance imaging (MRI) system, the steps comprising: a) acquiring image data from the lung using the MRI system and a pulse sequence that solicits an NMR response from lung tissue; b) reconstructing a lung density map from the image data acquired in step a) that indicates the density of lung tissue at each image pixel; c) filling the lung with a gas that includes a NMR responsive gas; d) acquiring magnetic resonance elastography (MRE) image data from the lung using the MRI system and a second pulse sequence that solicits an NMR response from the NMR responsive gas; e) reconstructing a spatial frequency map from the MRE image data acquired in step d) that indicates frequency of a strain wave at each image pixel; and f) calculating a shear modulus image from the lung density map and the spatial frequency map that indicates mechanical stiffness at each image pixel.