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Off-Resonance Angiography: A New Method to Depict Vessels—Phantom and Rabbit Studies¹

¹ From the Russell H. Morgan Department of Radiology and Radiological Science (G.K., S.S., E.J.V., W.D.G., M. Schär, L.T., D.L.K., R.G.W., M. Stuber) and Department of Medicine, Division of Cardiology (R.G.W.), Johns Hopkins University School of Medicine, 600 N Wolfe St, Park Bldg, Room 338, Baltimore, MD 21287; School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pa (R.C.B.); and Center for Molecular Imaging Research, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (D.E.S., R.W.). Received September 26, 2007; revision requested January 10, 2008; revision received February 26; accepted April 7; final version accepted April 17. Supported by NIH grants 1 K08 EB004922-01, R01 HL084186, R01 HL61912, and R24 CA92782, as well as by the Donald W. Reynolds Foundation. Address correspondence to M. Stuber (e-mail: mstuber{at}mri.jhu.edu).

Purpose: To evaluate the utility of inversion recovery with on-resonant water suppression (IRON) in combination with injection of the long-circulating monocrystalline iron oxide nanoparticle (MION)-47 for contrast material–enhanced magnetic resonance (MR) angiography.

Materials and Methods: Experiments were approved by the institutional animal care committee. Eleven rabbits were imaged at baseline before injection of a contrast agent and then serially 5–30 minutes, 2 hours, 1 day, and 3 days after a single intravenous bolus injection of 80 µmol of MION-47 per kilogram of body weight (n = 6) or 250 µmol/kg MION-47 (n = 5). Conventional T1-weighted MR angiography and IRON MR angiography were performed on a clinical 3.0-T imager. Signal-to-noise and contrast-to-noise ratios were measured in the aorta of rabbits in vivo. Venous blood was obtained from the rabbits before and after MION-47 injection for use in phantom studies.

Results: In vitro blood that contained MION-47 appeared signal attenuated on T1-weighted angiograms, while characteristic signal-enhanced dipolar fields were observed on IRON angiograms. In vivo, the vessel lumen was signal attenuated on T1-weighted MR angiograms after MION-47 injection, while IRON supported high intravascular contrast by simultaneously providing positive signal within the vessels and suppressing background tissue (mean contrast-to-noise ratio, 61.9 ± 12.4 [standard deviation] after injection vs 1.1 ± 0.4 at baseline, P < .001). Contrast-to-noise ratio was higher on IRON MR angiograms than on conventional T1-weighted MR angiograms (9.0 ± 2.5, P < .001 vs IRON MR angiography) and persisted up to 24 hours after MION-47 injection (76.2 ± 15.9, P < .001 vs baseline).

Conclusion: IRON MR angiography in conjunction with superparamagnetic nanoparticle administration provides high intravascular contrast over a long time and without the need for image subtraction.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2491071706/DC1

© RSNA, 2008

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