12. The method of claim 9 , wherein the different directions comprise orthogonal directions.
9. A reconstruction method, comprising: acquiring a set of projection data from a plurality of views around an imaged volume; performing an iterative reconstruction of the set of projection data by solving an objective function comprising at least a dictionary-based term, wherein the dictionary-based term employs dictionary learning that employs at least one dictionary comprising two-dimensional image patches oriented in different directions; and generating a reconstructed image upon completion of the iterative reconstruction.