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

Abstract

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 mol of MION-47 per kilogram of body weight (n ϭ 6) or 250 mol/kg MION-47 (n ϭ 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-tonoise ratio, 61.9 Ϯ 12.4 [standard deviation] after injection vs 1.1 Ϯ 0.4 at baseline, P Ͻ .001). Contrast-to-noise ratio was higher on IRON MR angiograms than on conventional T1-weighted MR angiograms (9.0 Ϯ 2.5, P Ͻ .001 vs IRON MR angiography) and persisted up to 24 hours after MION-47 injection (76.2 Ϯ 15.9, P Ͻ .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.

Nanomedicine Strategies for Molecular Targets with Mri and Optical Imaging

“…While both were reported to be effective, ferumoxytol had optimal luminal signal intensity 3 days post-treatment and ferumoxytol-treated rabbits had peak measurements 5 days after injection [11,8]. Recently, new magnetic resonance pulse sequences and image postprocessing techniques have been developed to reverse the dark contrast appearance into a bright positive contrast effect [119–126]. For example, inversion-recovery with ON-resonant water suppression (IRON) allowed the dark magnetic distortion artifacts associated with T 2 * USPIO imaging to be viewed as positive contrast that correlated with macrophage counts in hyperlipidemic rabbits best approximately 72 h post-treatment [123].…”

Theoretical and experimental study of ON-Resonance Saturation, an MRI sequence for positive contrast with superparamagnetic nanoparticles

“…Previous studies [38,[40][41][42][43] have demonstrated the possibility to get positive contrast with ONRS in vitro and in vivo but did not provide any theoretical understanding of the contrast dependence on the sequence and the SPM particle parameters.…”

“…Finally, the ON-Resonance Saturation method (ONRS) has been developed by Stuber et al [38], and tested in vivo in [39][40][41][42]. This sequence uses a saturation pulse to destroy the signal created by the on-resonance water protons, situated far from the SPM particles.…”

Iron Oxide Nanoparticles Imaging Tracking by MR Advanced Techniques: Dual-Contrast Approaches

“…The utility of IRON method combined with injection of the long-circulating MION-47 has been recently evaluated by investigators in Johns Hopkins University School of Medicine (Korosoglou, 2008a) for developing a novel contrast-enhanced MR angiography technique.…”