IRON magnetic resonance: a robust technique for angiography providing high blood-to-tissue contrast within the clinically approved dosage of superparamagnetic nanoparticles
KeywordsContrast Agent Abdominal Aorta Thoracic Aorta Image Subtraction Peripheral Vessel
Conventional MR angiography (MRA) exploits the property of exogenous contrast agents to shorten the T1 relaxation time. However, undesirable signal from surrounding tissue due to T1 recovery remains. IRON MRA is a promising off-resonance imaging technique, and provides in conjunction with superparamagnetic nanoparticles high intravascular contrast between the blood-pool and background tissue without need for image subtraction while T1 recovery of the surrounding tissue is no longer a problem.
Experiments were approved by the institutional animal care committee. Twelve rabbits were imaged at baseline and serially after the administration of 10 incremental dosages of 0.57 mg Fe (P904)/Kg. Conventional T1-weighted and IRON MRA were performed on a clinical 1.5-T imager. We performed angiography of the thoracic aorta (n=6), and angiography of the abdominal aorta and peripheral vessels (n=6). Contrast-to-noise ratios (CNR) were obtained in the thoracic and abdominal aorta of the rabbits and vessel sharpness was quantified in peripheral iliac and femoral vessels.
IRON MRA provides significantly higher blood-to-tissue contrast both in the aorta and in small peripheral rabbit vessels compared to T1-weigthed angiography within the dose range of approved for clinical human use. High CNR and vessel sharpness remain stable over a very wide range of contrast agent concentrations, which may possibly allow for more robust MRA acquisitions in clinical applications.
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