Time-of-flight magnetic resonance angiography is used for craniocervical arterial evaluation. Absent flow-related signal may be the result of slow flow, complex flow, or focal susceptibility effects. We report a case with complete absence of flow-related signal in the intracranial and cervical vessels due to ferumoxytol infusion given 5 days before magnetic resonance angiography. Ferumoxytol is a newly approved parenteral therapy for iron-deficiency anemia in patients with renal failure and awareness of this drug-magnetic resonance imaging interaction is needed.
