Objective Occupational exposure to Mn is subject to regulation due to potential neurotoxic effects. Mn-exposed animals show a selective deposition in the basal ganglia. Magnetic resonance imaging is a non-invasive method to assess the brain accumulation of Mn by a reduction of the T1 relaxation time (T1). Here, we explored the association between exposure to Mn and T1.

Material and methods We obtained data on T1 from the globus pallidus (GP), substantia nigra (SN), and frontal lobe (FL) in both hemispheres, Mn in blood (MnB), and carbohydrate-deficient transferrin (CDT) from 46 welders, 20 former welders, 31 men with Parkinson’s disease, 13 men with hemochromatosis, and 34 male controls. In active welders, respirable Mn was measured during one shift. Mixed models were applied to estimate group differences with controls as reference group, and the effects of Mn in blood or air on T1 for each region of interest adjusted for age and CDT.

Results Active welders had slightly lower T1 in the GP (indicative of Mn accumulation) than all other groups, although not significant and also not associated with airborne Mn. Former welders had no indication of a persistent Mn accumulation in this brain region. Increasing MnB resulted in reduced T1 signals in GP and FL, although the quality of the images influenced the effect estimate. In FL we observed higher T1 (indicative of lower metal concentrations) by increasing age and in hemochromatosis patients.

Conclusions Although Mn is strongly regulated in blood we found an association with T1 in GP and FL. However, effect estimates were influenced by the quality of the images. This innovative non-invasive method requires consensus about data quality and processing in epidemiological studies and on potential bias and confounding.