Sequential change of MR signal intensity of the brain after manganese administration in rabbits - Correlation with manganese concentration and histopathologic findings

RATIONALE AND OBJECTIVES. High signal intensity in the basal ganglia on T1- weighted MR imaging has been reported in chronic manganese (Mn) poisoning. However, the exact meaning of the high signal intensity remains unclear: do es it result from Mn itself, secondary pathologic changes of the brain tiss ue, or both? The goal of this study was to evaluate the sequential change o f MR signal intensity and to correlate the MR intensity of the globus palli dus and the hypothalamus with the Mn concentration in the blood and the bra in tissue, and with the histopathologic findings. METHODS. Ten milligrams per kilogram of Mn was administered once a week for 4 weeks to 14 rabbits. The rabbits in the control group (n = 2) were kille d without Mn administration; those in group I (n = 4) were killed 1 day aft er the completion of Mn administration, those in group II (n = 4) were kill ed at 4 weeks, and those in group III (n = 6) were killed at 8 weeks. Seque ntial MR imaging, blood and tissue concentration measurement, and pathologi c examination were performed. Sequential changes of the percent contrasts, contrast-to-noise ratios, and T1 relaxation times were analyzed with blood and tissue concentrations and histopathologic findings. RESULTS. The signal intensity of the basal ganglia on T1-weighted imaging w as highest 1 day after cessation of Mn administration and sequentially wash ed out. The contrast, contrast-to-noise ratio, and T1 relaxation time showe d significant correlations with blood concentration. Only the T1 relaxation time of the globus pallidus showed a significant correlation with tissue c oncentration. Histopathologic examination disclosed mild abnormalities in t he globus pallidus, thalamus, and hypothalamus. CONCLUSIONS. The high signal intensity on T1-weighted MR imaging presumably indicates mainly the exposure marker of Mn, although mild pathologic findi ngs were observed.