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Background
Ferumoxytol is an ultrasmall superparamagnetic iron oxide used off-label as an intravenous contrast agent for magnetic resonance imaging (MRI). Unlike gadolinium-based contrast agents (GBCAs), ferumoxytol remains in the intravascular space for an average half-life of 14-21 hours with studies demonstrating adequate intravascular signal for up to 72 hours after bolus administration. In this educational exhibit, we will demonstrate the benefit of ferumoxytol in transplant imaging.

Educational Goals / Teaching Points
Feromuxytol MRA can be used to identify transplant vasculature stenoses and thromboses as well as the presence of early collateralizations. Its use has been successfully demonstrated in renal, hepatic, and pancreatic transplantation. The prolonged plasma half-life of ferumoxytol allows for exquisite high-resolution base acquisitions, which can then be utilized in three-dimensional reconstruction. Other obtainable sequences include dynamic TWIST to generate virtual angiograms and curved planar maximal intensity projections to display vascular anatomy much like catheter angiography. Coadministration with GBCAs allows for additional imaging utility as well. With ferumoxytol’s extended plasma half-life, imaging protocols can be optimized around gadolinium excretion into the collecting system, enabling one study to localize both urinary and vascular lesions. Examples of ferumoxytol’s clinical utility include identification of transplant renal artery stenosis, simultaneous transplant renal artery stenosis and ureteral stricture, renal vein stenosis with capsular collateralization, hepatic artery thrombosis with collateralization, transplant portal vein thrombosis, extensive transplant pancreas vein thrombosis with simultaneous renal transplant artery and vein stenosis, and a technical artifact mimicking stenosis. In these cases, ultrasound and traditional cross-sectional imaging were equivocal or nondiagnostic.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Ferumoxytol-enhanced MRA in solid organ transplant evaluation provides strong technical advantages for vascular imaging beyond traditional GBCA MRA and CTA alone, facilitating evaluation of treatment-altering lesions earlier in presentation.

Conclusion
In this educational exhibit, we provide a case-based review of ferumoxytol MRA to illustrate its benefits in transplant imaging. Selected cases demonstrate use cases and technical advantages of ferumoxytol including high-resolution vascular imaging without background parenchymal activity and repeat imaging without additional contrast. Specific examples of virtual angiography and coadministration of GBCAs are highlighted. In these cases, ultrasound and traditional cross-sectional imaging were equivocal or nondiagnostic. Additional cases will highlight: renal vein stenosis with capsular collateralization (treatment altering), hepatic artery thrombosis with collateralization, transplant portal vein thrombosis, extensive transplant pancreas vein thrombosis with simultaneous renal transplant artery and vein stenosis, and a technical artifact mimicking stenosis.