Enhancement of phase-contrast MR angiography with superparamagnetic iron oxide

The effect of superparamagnetic iron oxide particles (AMI-227) was assessed in three-dimensional (3D) phase-contrast (PC) MR angiography (MRA), with various scanning parameters for rats at 1.5 T. The blood T1 and T2 before and after 20 micromol Fe/kg of AMI-227 injection were measured sequentially at .47 T. The visualization of abdominal aorta, renal artery, inferior vena cava, and portal vein was respectively evaluated before and after AMI-227 injection qualitatively by the four confidence levels and quantitatively by analysis of signal-to-noise ratio (SNR) of vessels. The blood T1 and T2 were sufficiently shortened for at least 1 hour after AMI-227 injection. The visualization of each vessel was improved by AMI-227 at various velocity encoding (VENC) value, suggesting the extended application of PC-MRA in various conditions. The optimal flip angle was increased from 20 degrees to 30 degrees in higher VENC after AMI-227 injection, resulting in higher signal from blood flow. Quantitative analyses showed that the optimal flip angle to achieve the maximum SNR seemed to be 20 degrees in unenhanced images, but the optimal flip angle of the high speed flow was increased by contrast enhancement. The postcontrast PC-MRA provides the increased sensitivity of slow flow components, even with a high VENC gradient. AMI-227 can significantly improve SNR to blood vessels during 3D-PC-MRA with various scanning parameters.