Magnetic resonance imaging of monkey placenta with manganese enhancement

Magnetic resonance imaging of pregnant cynomolgus monkeys in the last trimester was done on a Picker instrument (Picker International, Inc. 11 Northford, Connecticut) operating at 0.26 tesla. Both inversion-recovery and spin-echo proton images were obtained, demonstrating good detail of fetal and maternal anatomy. The placenta was particularly easy to identify, and its image was further enhanced by a bolus infusion of manganese chloride. Manganese is one of several paramagnetic ions that shortens proton relaxation times, and as a result alters signal intensity in magnetic resonance imaging. An infusion of 10 μmol/kg of manganese chloride was chosen on the basis of an in vitro experiment demonstrating shortening of the spin-lattice relaxation time at increasing concentrations of manganese. Additional studies showed rapid serum clearance of manganese after an intravenous dose with subsequent rapid uptake in the placenta. These results demonstrate that manganese is potentially suitable for studying placental blood flow with magnetic resonance imaging.