1 Division of Neuroimaging and Neurointervention, Department of Radiology, Stanford University School of Medicine, Stanford Health Care, Stanford Initiative for Multimodality Neuro-Imaging in Translational Anatomy Research (SIMITAR), Center for Academic Medicine, Radiology MC: 5659, 453 Quarry Road, Palo Alto, CA 94304, USA. Electronic address: tmassoud@stanford.edu.