Neuroimaging in manganism.

Neuroimaging such as magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) have been used in the last decade for investigating the neurotoxicolgy of manganese (Mn). Increased signal intensities on a T1-weighted image may reflect increased Mn deposits (e.g., due to exposure to Mn) but not necessarily manganism. In a biologically based dose-response model, our recent results strongly suggest that signal intensities in T1-weighted MRI reflect a target site dose. However, the threshold of signal intensity associated with clinical symptoms of manganism remains to be solved. Functional neuroimaging such as PET or SPECT examines the integrity of the nigrostriatal dopaminergic system, and thus is very important for the differential diagnosis of manganism. However, neuroimaging research should also aim at developing specific and sensitive parameters for manganism in Mn-exposed individuals.