1. A method comprising: acquiring first modality image data while an imaged object moves over a range of motion and reconstructing the first modality image data into a motion artifacted first modality image, the first modality image being one of a positron emission tomography (PET) image or a single positron emission computed tomography (SPECT) image; acquiring second modality image data and reconstructing the second modality image data into second modality images which represent the object in respective states of motion with as few motion artifacts as possible, the second modality images being one of computed tomography (CT) images and magnetic resonance (MR) images; from the second modality images, determining a motion model which characterizes states of motion assumed by the object while moving through the states of motion; forming an intermediate image of the object from the motion model and the second modality images, the intermediate image representing the object as if it had moved during the acquiring of the second modality image data over the range of motion over which the object moved as the first modality imaging data was acquired, forming the intermediate image includes: forming other images of other states of motion of the object from the second modality image data; weighting and subsequently superimposing the other images and the second modality images in conformity with a frequency at which each of the other states of motion were assumed by the object while moving over the range of motion while the first modality image data was acquired; forming a combination image from the intermediate image and the first modality image.