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 mumol 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 mumol 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.