1. An imaging system for compensating for mask frame misalignment with non-mask frames in an image sequence, comprising: an image data processor for: determining a compensation zoom factor for individual image frames of an image sequence in response to data indicating distance between an object of interest and a radiation detector for said individual image frames, associating individual zoom factors with corresponding individual image frames of said image sequence, storing said individual zoom factors associated with corresponding individual image frames of said image sequence in a repository, applying an individual determined zoom factor to align an associated corresponding image frame and a mask frame comprising an image frame of the image sequence prior to detection of contrast agent, to provide an aligned image frame; and determining data representing an image difference frame comprising a difference between data representing said aligned image frame and a mask frame; and a user interface for generating data representing a display image presenting said image difference frame.