1. A method for reconstructing a time series of image frames of a subject with an imaging system, the steps comprising: a) acquiring, with the imaging system, image data from the subject; b) producing a prior image using the acquired image data; c) producing a plurality of image frame estimates using the acquired image data and the prior image; d) reconstructing a plurality of image frames using the prior image and the plurality of image frame estimates; and e) iteratively repeating step d) until a stopping criterion is satisfied, wherein the plurality of image frame estimates are updated after each iteration.