1 Division of Neuroradiology, Department of Radiology, University of North Carolina School of Medicine, 3326 Old Infirmary, Campus Box 7510, Chapel Hill, NC 27599-7510, USA. Electronic address: carlos_zamora@med.unc.edu.
2 Department of Radiology, University of North Carolina School of Medicine, 3327 Old Infirmary, Campus Box 7510, Chapel Hill, NC 27599-7510, USA. Electronic address: mauricio_castillo@med.unc.edu.