1. A method for retrospective internal gating comprising: acquiring a series of images at times t 1. .. tn; extracting time-activity information for individual voxels; prioritizing voxels for phase analysis, and assigning weighting factors; applying frequency filter to voxel time-activity curves; using prioritization, combining voxel time-activity information into a time varying object motion function; using the time varying object motion function for the mapping of image data to corresponding motion phases; and using the mapping of image data to corresponding motion phases to generate at least one motion corrected image.