Fractionated manganese-enhanced MRI.

We investigated the use of manganese-enhanced MRI (MEMRI) with fractionated doses as a way to retain the unique properties of manganese as a neuronal contrast agent while lessening its toxic effects in animals. First, we followed the signal enhancement on T1-weighted images of the brains of rats receiving 30 mg/kg fractions of MnCl2 . 4H2O every 48 h and found that the signal increased in regions with consecutive fractionated doses and ultimately saturated. Second, we used T1 mapping to test whether the amount of MRI-visible manganese that accumulated depended on the concentration of manganese in the fractions. For a fixed cumulative dose of 180 mg/kg MnCl2 . 4H2O, increasing fraction doses of 6 x 30 mg/kg, 3 x 60 mg/kg, 2 x 90 mg/kg and 1 x 180 mg/kg produced progressively shorter T1 values. The adverse systemic health effects, including complications at the injection site and poor animal well-being, also rose with the fraction dose. Thus, fractionated MEMRI can be used to balance the properties of manganese as a contrast agent in animals against its toxic effects.