Figure 1: Interpreting the contribution of iron to MRI signal in the substantia nigra of an elderly case without Parkinson's disease.

a, Photograph showing brown deposits of neuromelanin, typically found in dopaminergic neurons (scale bar, 1 mm). b, Corresponding X-ray fluorescence map of iron distribution from low (blue) to high (red) concentration (scale bar, 1 mm). c, T2* MRI microscopy in original block of unfixed tissue (scale bar, 500 μm). For further details, see ref. 6. Picture credits: J. F. Collingwood (a–c), University of Warwick; M. R. Davidson (b), A. Mikhailova (a), J. P. Bullivant (c), V. Antharam (a, c), C. Batich (c) and J. Forder (c), University of Florida; J. Dobson (b), Keele University; and P. D. Quinn (b) and J. F. W. Mosselmans (b), Diamond Light Source.