[1] Univ Helsinki, Cent Hosp, Dept Neurol, FIN-00290 Helsinki, Finland
[2] Univ Helsinki, Cent Hosp, Dept Radiol, FIN-00290 Helsinki, Finland
[3] Univ Helsinki, Dept Phys Sci, FIN-00014 Helsinki, Finland
[4] Aarhus Univ Hosp, Dept Neuroradiol, DK-8000 Aarhus, Denmark
[5] Synarc Inc, San Francisco, CA USA
[6] Helsinki Brain Res Ctr, Funct Brain Imaging Unit, Helsinki, Finland