1. From the Neuroradiology Research Laboratory (D.D., Y.H.D., M.A.D., R.K., D.A.L., H.J.C., D.F.K.), Department of Radiology, Mayo Clinic, Rochester, Minn; the Department of Physiology and Biomedical Engineering (L.W.H., W.-Z.Z., G.C.S.), Mayo Clinic, Rochester, Minn; and the Department of Neurosurgery (G.A.H.), University of Virginia, Charlottesville, Va.