A schematic of the PET imaging protocol used to study the healthy volunteers. The imaging protocol consisted of 5 sub-studies: 15O-water (before cyclosporine infusion, for evaluation of regional cerebral blood flow), 11C-verapamil (before cyclosporine infusion, for evaluation of regional P-gp activity at the BBB), 15O-water (during cyclosporine infusion, approximately 1 hr after onset of the cyclosporine infusion), 11C-verapamil (during cyclosporine infusion), and 11C-CO (for evaluation of tissue vascular volume).