[1] Univ Washington, Sch Med, Dept Neurol, Seattle, WA 98104 USA
[2] Ernst Moritz Arndt Univ Greifswald, Dept Neurol, Greifswald, Germany
[3] Univ Washington, Sch Med, Dept Biostat, Seattle, WA 98104 USA
[4] Univ Washington, Sch Med, Dept Radiol, Seattle, WA 98104 USA