1 Magnetic resonance imaging perfusion is associated with disease severity and activity in multiple sclerosis Piotr Sowa (1, 2), Gro Owren Nygaard (3), Atle Bjørnerud (4, 5), Elisabeth Gulowsen Celius (3, 6), Hanne Finstad Harbo (2, 3), Mona Kristiansen Beyer (1, 7) (1) Department of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway (2) Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway (3) Department of Neurology, Oslo University Hospital, Oslo, Norway (4) Intervention Center, Oslo University Hospital, Oslo, Norway (5) Department of Physics, University of Oslo, Oslo, Norway (6) Institute of Health and Society, Faculty of Medicine, University of Oslo, Oslo, Norway (7) Department of Life Sciences and Health, Oslo and Akershus University College of Applied Sciences, Oslo, Norway ABSTRACT Purpose The utility of perfusion weighted imaging in multiple sclerosis (MS) is not well investigated. The purpose of this study was to compare baseline normalized perfusion measures in subgroups of newly diagnosed MS patients. We wanted to test the hypothesis that this method can differentiate between groups defined according to disease severity and disease activity at one year follow-up. Methods Baseline magnetic resonance imaging (MRI) including a dynamic susceptibility contrast perfusion sequence was performed on a 1.5 Tesla scanner in 66 patients newly diagnosed with relapsing-remitting MS. From the baseline MRI, cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) maps were generated. Normalized (n) perfusion values were calculated by dividing each perfusion parameter obtained in white matter lesions by the same parameter obtained in normal appearing white matter. Neurological examination was performed at baseline and at follow-up approximately one year later to establish the multiple sclerosis severity score (MSSS) and evidence of disease activity (EDA).