1. From the Department of Radiology (J.S.M., A.B.K., C.H.H., J.J.S., R.P.H., D.F.K., R.J.M.), Department of Quantitative Health Sciences (N.B.L.), Division of Allergic Diseases (D.E.M.), and Department of Neurosurgery (D.F.K.), Mayo Clinic, 200 1st St SW, Rochester, MN 55905.