1The Intervention Centre, Oslo University Hospital, Oslo, Norway, 2Dept. of Physics, University of Oslo, Oslo, Norway, 3Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States, 4Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States, 5Center for Neuro-Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, United States, 6Siemens Healthcare Health Services, Malvern, MA, United States, 7MGH-HST A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States