Synopsis
Ferumoxytol has seen increasing use as a contrast agent in both clinical and research MRI. This talk will describe some of the potential uses and risks associated with the agent.
Ferumoxytol - what is it?
Ferumoxytol
is an ultrasmall superparamagnetic iron oxide (USPIO) agent initially approved
by the Food and Drug Administration (FDA) as an iron replacement therapy for
patients with anemia due to chronic renal failure. It is composed of iron oxide
particles surrounded by a carbohydrate coat. Recently, ferumoxytol has been
investigated extensively as an intravenous contrast agent in magnetic resonance
imaging (MRI). It has been postulated as an alternative to gadolinium-based
contrast agents (GBCAs) in patients in whom GBCA administration is
contraindicated due to renal dysfunction, dialysis dependence, and other risk
factors for nephrogenic systemic fibrosis (NSF).
What can it be used for?
Since
it causes regional T1 and T2 * shortening in vivo, conventional pulse sequences
can be used following ferumoxytol administration to demonstrate signal
enhancement or loss. Ferumoxytol can be administered as either a rapid bolus or
slow infusion, though the FDA advises against bolus administration. It has a long intravascular half-life on the
order of 14-15 hours, making it a potentially useful agent for vascular and
perfusion-weighted MRI.
A
variety of intravascular applications of ferumoxytol have been described,
including aortoiliac imaging, assessment for endoleaks after stent-graft
repair, DVT imaging, and renal transplant vascular imaging. In addition, it may
have utility as an intravascular contrast agent in assessing vascular invasion
by tumors such as renal cell carcinoma and hepatocellular carcinoma, in
patients who cannot receive GBCAs.
Ferumoxytol
is ultimately taken up by macrophages and broken down, with trafficking of the
iron moieties into the reticuloendothelial system in the liver, spleen, and
lymph nodes. This uptake mechanism is
being explored as a novel imaging technique for vascular lesions, tumors, and
lymph nodes. In this setting,
ferumoxytol functions as an in vivo
label for macrophages and can be used to track macrophage localization. Small studies have suggested that cerebral
aneurysms and carotid plaques at elevated risk for rupture can be
differentiated from stable lesions based on localization of ferumoxytol-labeled
macrophages. Imaging for lymph node
metastases has also been described, based on absence of macrophage/ferumoxytol
accumulation in nodes replaced by metastasis.
Brain tumor imaging using the same mechanism has also been described.
What are the risks?
In
comparison to other USPIOs, ferumoxytol is less limited by allergic and
idiosyncratic reactions. However,
serious reactions to ferumoxytol administration have been described, including
hypotension and anaphylaxis. Reaction
rates appear to be higher than those associated with gadolinium-based contrast
agents, thus risks and benefits must be weighted carefully prior to choosing to
administer ferumoxytol. Like any
medication, ferumoxytol must be administered in a setting where appropriate
support and timely response to reactions is available.
Acknowledgements
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