1. A method of assessing lung function using a first set of lung volumetric images obtained at inspiration and a second set of volumetric images obtained at expiration, the method comprising: a) processing the first and second set of images to identify known anatomical structures of the lungs; b) registering the first set of images to the second set of images to match voxels of the first set of images to voxels of the second set of images as matched pairs of inspiratory and expiratory voxels; c) calculating a continuous probability of a lung characteristic at a location of the matched pairs of voxels of step b); d) displaying a result of step c) on a display.