1Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tuebingen, Tuebingen, Germany, 2Institute of Signal Processing and System Theory, University of Stuttgart, Stuttgart, Germany, 3Department of Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, Germany, 4Section on Experimental Radiology, Department of Radiology, University Hospital Tuebingen, Tuebingen, Germany