Detecting temperature-driven microstructural modulations in tissue using diffusion MRI

In this study, we uncover that the signal fraction of a fully restricted diffusion compartment in fixed white matter tissue, the so-called dot fraction, is dependent on the tissue temperature. In particular, we report a sudden increase in its nominal value of this fraction when the tissue temperature drops below approximately 32°C. The underlying mechanism remains unexplained, but its impact on modeling of ex vivo diffusion MRI cannot be underestimated. The observation corroborates our hypotheses of a temperature-dependent disruption of the multilamellar structure of the myelin sheath, leading to water trapped in vacuoles that are formed in the myelin sheath.