A Study of Two Methodologies for Measuring Blood Flow in the Brain in Response to Non-Drug Stimuli (P08085/MK-0000-180)

This study will identify a dose of ferumoxytol that can reliably detect changes in blood flow/volume in response to non-drug stimuli. The study will determine whether signal detection for functional magnetic resonance imaging (fMRI) using ferumoxytol is better than that for blood oxygen level-dependent (BOLD) fMRI in response to sensory stimulation. The following procedures will be conducted in each of two study periods: arterial spin labeling (ASL) imaging study with increasing exposure to carbon dioxide (CO2); BOLD fMRI study with sensory stimulation; MRI studies with sensory stimulation in the presence of increasing doses of ferumoxytol; MRI study with increasing exposure to CO2 in the presence of ferumoxytol. There will be a 3-week interval between the two study periods. The study will enroll 8 subjects, but an additional 4 subjects are permitted to enroll to preserve study power.