Temporal changes in the T1 and T2 relaxation rates (ΔR1 and ΔR2) in the rat brain are consistent with the tissue-clearance rates of elemental manganese

Temporal changes in the T and T relaxation rates (ΔR and ΔR) in rat olfactory bulb (OB) and cortex were compared with the absolute manganese (Mn) concentrations from the corresponding excised tissue samples. In vivo T and T relaxation times were measured before, and at 1, 7, 28, and 35 d after intravenous infusion of 176 mg/kg MnCl. The values of ΔR , ΔR, and absolute Mn concentration peaked at day 1 and then declined to near control levels after 28 to 35 d. The Mn bioelimination rate from the rat brain was significantly faster than that reported using radioisotope techniques. The R and R relaxation rates were linearly proportional to the underlying tissue Mn concentration and reflect the total absolute amount of Mn present in the tissue. The in vivo Mn r and r tissue relaxivities were comparable to the in vitro values for aqueous Mn. These results demonstrate that loss of manganese-enhanced MRI (MEMRI) contrast after systemic Mn administration is due to elimination of Mn from the brain