Application of superparamagnetic iron oxide (AMI-227) for 3D phase-contrast MR angiography.

Abstract

Time-of-flight (TOF) MR angiography (MRA) has been utilized in evaluating vascular abnormalities, although there is still a limitation of saturation effect of intravascular spins in imaging slab. The use of contrast material is one of the solutions to reduce the saturation effect. Gadolinium (Gd)-chelating MR contrast agents have been applied for TOF MRA, particularly in body MRA within a short period (1,2). Recently, ultrasmall superparamagnetic iron oxide (USPIO) particles, targeted to RES (reticuloendothelial system), have been applied to TOF MRA (3,4). Their greater T1 relaxivity and longer blood half-life than Gd chelates are additionally promising for MRA. A disadvantage of using Gd chelates in TOF MRA is enhanced background, which is overlaid on vascular structares under maximum-intensity-projection (MIP) method. This problem can be circumvented by three-dimensional (3D) phase-contrast (PC) MRA. The advantage of contrast-enhanced PC MRA over contrast-enhanced TOF MRA is that all stationary tissues are subtracted in PC MRA, improving the visualization of small vessels with signal intensity close to the background. Although the clinical application of Gd-based MR contrast agents for PC MRA has been documented (5,6), the effect of USPIOs in PC MRA is not investigated. In this study, we applied USPIOs for 3D PC MRA and evaluated the efficacy in various scanning parameters.