1High Field MR Center, Max Planck Institute for biol. Cybernetics, Tuebingen, Germany, 2IMPRS for Cognitive and Systems Neuroscience University of Tuebingen, Tuebingen, Germany, 3Institute of Microelectronics, University of Ulm, Ulm, Germany, 4Institute for Biomedical Engineering, ETH Zürich, Zurich, Switzerland, 5Univ Copenhagen, Hvidovre Hosp, Danish Res Ctr Magnet Resonance, Hvidovre, Denmark, 6Tech Univ Denmark, Biomed Engn Sect, Lyngby, Denmark, 7Department of Biomedical Magnetic Resonance, University Tuebingen, Tuebingen, Germany