1. A method for reducing the effect of physiological motion in image data acquired from a sequence of medical images of a subject comprising: acquiring a sequence of medical images containing image data of a target region of a subject during the occurrence of cyclical physiological motion affecting the target region; using changes in image data in a region of at least some of the images in the sequence to identify cycles of the physiological motion; identifying images acquired during a certain range of phases of the identified motion cycles; and processing image data of the identified images to assess a property of the target region.