1. A method for validating non-rigid image registration, comprising: acquiring a source image and a target image; performing registration from source image to target image using a non-rigid registration technique to produce a forward transformation map; performing registration from the target image back to the source image using the non-rigid registration technique to produce a backward transformation map; measuring consistency registration error as an indication of a change in local volume of the source with respect to the target image using the produced forward transformation map and the produced backward transformation map; and validating the non-rigid registration technique based on the measured consistency registration error.