Contrast‐enhanced 3D‐TOF MRA of peripheral vessels: Intravascular versus extracellular MR contrast media

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Abstract
MR contrast media have been used to improve MR angiography (MRA). Their effect has been particularly beneficial for extracranial MRA. This study evaluated the efficacy of a new formulation of ultrasmall super‐paramagnetic iron oxide particles (USPIO) on three‐dimensional (3D) time of flight (TOF) MRA in the pelvis and lower limb circulation. Each of six dogs received 3 mg/kg of USPIO and .2 mmol/kg of gadolinium‐dieth‐ylenetriamine pentaacetic acid (Gd‐DTPA) bis‐meth‐ylamide (BMA) by intravenous infusion on separate examinations. Precontrast and postcontrast 3D‐TOF MRA images of the lower extremities were acquired over the course of 45 minutes postinjection. Signal intensity (SI) was measured on axial views along the external iliac, femoral, and popliteal arteries. USPIO provided clear demarcation of the major primary, secondary, and tertiary vessels and the improved contrast‐to‐noise ratio (CNR) was maintained for 45 minutes. Gd‐DTPA‐BMA provided less signal enhancement than USPIO. The increase in CNR with this agent had significantly declined by 15 minutes after injection. The major vessels could no longer be visualized at 30 and 45 minutes after injection of Gd‐DTPA‐BMA. This study demonstrates the efficacy of USPIO as a contrast medium for 3D‐TOF MRA. It was concluded that USPIO provided effective and persistent enhancement of the peripheral vessels.