1Department of Radiology and Nuclear Medicine, St. Olav's University Hospital, Trondheim, Norway, 2IMTEK - Laboratory for Simulation, University of Freiburg, Freiburg, Germany, 3Institute of Microstructure Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany, 4IMTEK - Laboratory for Microactuators, University of Freiburg, Freiburg, Germany