Lateral diffusion of manganese in the rat brain determined by T(1) relaxation time measured by (1)H MRI

In order to optimize manganese ion-enhanced MRI in thalamic and hypothalamic nuclei, we analyzed the diffusion of manganese in the brain followed by the intra-cerebroventricular application of manganese-bicine (Mn-bicine). T(1)-weighted MRI intensities, with 9-pixel ROIs in the hypothalamus perpendicular to the third ventricle, were measured during continuous infusion of Mn-bicine solution in the lateral cerebroventricle. Using a relationship between the image intensity of T(1)-weighted MRI and T(1) relaxation time, the image intensity was converted into the concentration of manganese. Assuming a simple diffusion process, the apparent diffusion coefficient (D (ap)) of manganese (4.2 × 10(-5) mm(2) s(-1)) is much lower than that of water (6 × 10(-4) mm(2) s(-1)), and the D (ap) tended to decrease when the distance from the third ventricle increased. These results suggest (1) the Mn(2+) ion is trapped by neural cells during diffusion and (2) the manganese efflux is discharged from the brain via veins.