[1] Univ Utah, Dept Radiol, Salt Lake City, UT 84132 USA
[2] Univ Utah, Dept Imaging Sci, Salt Lake City, UT 84132 USA
[3] Univ Utah, Dept Neurosurg, Salt Lake City, UT 84132 USA
[4] Univ Utah, Dept Neurol, Salt Lake City, UT USA
[5] Univ Washington, Dept Radiol, Seattle, WA 98195 USA