1. Divisions of Molecular Surface Physics and Nanoscience, Chemistry, and Applied Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden, Center for Medical Image Science and Visualization (CMIV), Linköping University, SE-581 85 Linköping, Sweden, and Department of Medical and Health Sciences (IMH)/Radiology, Linköping University, SE-581 85 Linköping, Sweden