ENHANCEMENT OF MR-ANGIOGRAPHY WITH IRON-OXIDE - PRELIMINARY STUDIES IN WHOLE-BLOOD PHANTOM AND IN ANIMALS

OBJECTIVE. We hypothesized that the previously observed T1 effect of a small monocrystalline iron oxide preparation can be exploited to decrease T1 relaxation time of blood. Such a decrease, particularly if present for a long time, could be used to improve the quality of MR angiograms. To test the hypothesis, we performed phantom studies and in vivo animal experiments. MATERIALS AND METHODS. The effect of the monocrystalline iron oxide preparation on the MR signal intensity (spoiled gradient-recalled acquisition in the steady state pulse sequences, various timing parameters) of human whole blood was first tested in a phantom (dose range of monocrystalline iron oxide preparation, 0-3 mu mol Fe/ml). Subsequent experiments were performed in rats (n=7) and in rabbits (n=6) to determine whether predicted changes in signal intensity could be observed in vivo. RESULTS. Dose optimization studies in rats indicate that injected doses of 15-50 mu mol Fe/kg (0.8-2.8 mg Fe/kg) of monocrystalline iron oxide preparation resulted in threefold to fourfold increases of aortic signal-to-noise ratio. Because of its long plasma half-life (180 min in rats), the iron oxide preparation markedly improved the quality of images of the vasculature of the lungs, abdomen, and extremities. CONCLUSION. Our experimental results suggest that this and possibly other iron oxide preparations are alternatives to compounds containing macromolecular gadolinium and could be useful for clinical MR angiography.