[1] Univ Penn, Perelman Sch Med, Philadelphia, PA 19104 USA
[2] Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA
[3] Univ Calif San Francisco, Dept Radiol & Biomed Imaging, San Francisco, CA 94143 USA
[4] Cleveland Clin, Imaging Inst, Cleveland, OH 44106 USA
[5] Univ Texas Austin, Dell Med Sch, Dept Diagnost Med, Austin, TX 78712 USA
[6] Univ Penn, Dept Neurosurg, Philadelphia, PA 19104 USA