The appropriate concentration of a metal lies within a very narrow range, and any excess or shortage easily causes toxic effects in vivo. On the other hand, excess amounts of such metals induce cellular and tissue damage, leading to a variety of adverse effects and diseases. Several metals are essential nutrients in humans, and metal shortages lead to a variety of deficiency diseases or syndromes. Metals play an important role in diverse biochemical and physiological functions in humans, and various enzymes and vitamins contain metals. Thus, when analyzing metal deposition using MRI, caution should be exercised when interpreting the validity and reliability of the obtained data. However, because nonparamagnetic materials and other coexisting metals also affect the signal intensity of brain MRI, the quantitative analysis of metal concentrations is difficult. Typically, manganese overload causes high signal intensity on T1-weighted images (T1WI) in the globus pallidus, iron overload causes low signal intensity in the globus pallidus on T2-weighted images, and gadolinium deposition causes high signal intensity in the dentate nucleus, globus pallidus, and pulvinar of thalamus on T1WI. We reviewed the history of brain metal analysis with histologic findings. However, the brain contains many kinds of metals that affect the signal intensity of MRI, which has led to numerous misunderstandings in the history of metal analysis. Metal concentration abnormalities may cause metal deposition in the brain, and magnetic resonance imaging (MRI) is the most potent and sensitive technique now available for detecting metal deposition given the difficulties associated with performing brain tissue biopsy. Various metals are essential nutrients in humans, and metal shortages lead to a variety of deficiency diseases.
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