Experimental study of the pharmacokinetics and dose response of ferrite particles used as a contrast agent in MRI of the normal liver of the rabbit.

Superparamagnetic ferrite is a specific magnetic resonance imaging (MRI) contrast agent for the liver and the spleen. The large electronic magnetic moments of the ferrite particles create local field inhomogeneities that shorten the transversal relaxation time and reduce the spin-echo amplitude and the intensity of the liver and spleen signals in MR images. MRI was performed at 1.5 T using a SE sequence with TR/TE = 300/15 milliseconds. Pharmacokinetics were studied on five rabbits during five hours and up to 11 days after ferrite injection with doses ranging from 0.2 to 1 mg Fe/kg. Dose responses (0.2 mg to 8 mg Fe/kg) were studied on 11 additional rabbits, at three hours and three days after injection. Results show that the effect of ferrite on the liver images is stable between 30 minutes and 6 hours, and that the liver images recover their intensities before injection after about two days. The liver intensity drops to half its value for a dose of 1.25 mg Fe/kg (for TR/TE = 300/15 milliseconds). Our results support the conclusions from studies on other animal species that ferrite should be considered a useful MRI contrast agent for clinical investigations of the liver.