1Computer Science and Engineering, University of Oulu, Oulu, Finland, 2Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland, 3Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland, 4Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland, 5Department of Applied Physics, University of Eastern Finland, Kuopio, Finland, 6Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland