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.

Study Design: Translational Medicine - Imaging Platform Development

Inclusion Criteria:

• Participant weighs approximately 55-75 kg and has a Body Mass Index (BMI) of 18-25 kg/m^2
• Participant is in good health
• Participant is a nonsmoker and/or has not used nicotine or nicotine-containing products for at least 6 months

Exclusion Criteria:

• Participant has a contraindication to MRI including cardiac pacemaker, brain aneurysm clip, implanted neurostimulator, insulin pump, cochlear implant, metal slivers in the eyes, or any other MRI-incompatible metal implants that cannot be safely removed
• Participant has a condition that would limit his ability to complete MRI procedures, such as claustrophobia or chronic back pain
• Participant plans to undergo MRI studies in the 3 months following the post-study visit
• Participant has a history of hemochromatosis or other conditions of iron overload or disease of iron metabolism
• Participant has a known sensitivity to ferumoxytol or iron-containing products or has a history of severe allergies, anaphylactic reaction, or intolerance to drugs and/or foods
• Participant has a history of stroke, chronic seizures, or major neurological disorder
• Participant is unable to refrain from the use of any medication, including prescription and non-prescription drugs or herbal remedies from approximately 2 weeks prior to the first dose of ferumoxytol until the post-study visit
• Participant has a history of significant head injury/trauma with loss of consciousness lasting for 15 minutes and one or more of the following: a) recurring seizures resulting from head injury; b) persistent neurological or cognitive sequelae of the injury; c) cognitive rehabilitation following the injury