Longitudinal Analysis of Quantitative Brain MRI in Astronauts Following Microgravity Exposure

Background and purpose: Assessment of the effects of microgravity on astronauts' brains using microstructural measures by utilizing quantitative MRI, before and after spaceflight would help understand the structural changes.

Methods: Quantitative MRI data sets in 19 astronauts were acquired before and after space missions. Both diffusion tensor metrics and volumetric measures were analyzed in the brain regions involved in the visual function.

Results: The fractional anisotropy was reduced in the right posterior thalamic radiations (P = .0009) and remained significant after a false discovery rate (FDR) correction (P = .03). A trend of increase in the mean diffusivities of different subregions of the occipital cortex on the right side, including calcarine, middle occipital, inferior occipital, and fusiform gyri, was noted and became insignificant after FDR correction. Similarly, there was a trend of cortical thinning involving the right occipital lobe and bilateral fusiform gyri, volume reduction of the left thalamus, and increase in lateral ventricular volume in the postflight scans.

Conclusion: Gray and white matter alterations are detected by quantitative MRI before and after space flight. Our findings may be used to understand the neuroanatomical mechanisms of possible brain dysfunction or neuroplasticity in microgravity condition in the future studies.