1. Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, Aachen 52056, Germany
2. Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, 13 South Drive, Bethesda, Maryland 20892, United States
3. Institut Laue-Langevin, DS/LSS, 71 Avenue des Martyrs, CS 20156, Grenoble Cedex 9 38042, France