Significance of Brain Magnetic Resonance Imaging (MRI) in the Assessment of Occupational Manganese Exposure

ABSTRACT

Manganese is an essential element in the body. It is mainly diposited in the liver and to a lesser degree in the basal ganglia of the brain and eliminated through the bile duct. Rapid turnover of manganese in the body makes it difficult to evaluate the manganese exposure in worker, especially in those with irregular or intermittent exposure, like welder. Therefore, conventional biomarkers, including blood and urine manganese can provide only a limited information about the long-term or cumulative exposure to manganese. Introduction of magnetic resonance imaging (MRI) made a progress in the assessment of manganese exposure in the medical conditions related to manganese aculmulation, e. g., relaxation time on MRI due to its paramagnetic property, resulting in high signal intensity(HSI) on T1-weighted image(T1WI) of MRI. Manganese deposition int he brain, therefore, can be visualized as an HSI in the globus pallidus, the substantia nigra, the putamen and the pituitary. Clinical and epidemiologic studies regarding the MRI findings in the cases of occupational and non-occupational manganese exposure were reviewed. Relationships between HSI on T1WI of MRI and age, gender, occupational manganese exposure, and neurological dysfunction were analysed. Relationship between biological exposure indices and HSI on MRI were also reviewed. Literatures were reviewed to establish the relationships between HSI, manganese deposition in the brain, pathologic findings, and neurological dysfunction. HSI on T1WI of MRI reflects regional manganese deposition in the brain. This relationship enables an estimation of regional manganese deposition in the brain by analysing MR signal intensity. Manganese deposition in the brain can induce a neuronal loss in the basal ganglia but functional abnormality is supposed to be related to the cumulative exposure of manganese is relatively too short to reflect the long-term cumulative exposure of manganese in the brain, use of brain MRI for the assessment of exposure in a group of workers seems to be hardly rationalized, while it can be a useful adjunct for the evaluation of manganese exposure in the cases with suspected manganese-related health problems.