Abstract #3764

From in situ to ex vivo: the effect of autolysis and fixation on quantitative MRI markers for myelin

Siawoosh Mohammadi^1,2,3, Jan Sedlacik⁴, Martina F Callaghan², Jens Fiehler⁴, Gunther Helms⁵, and Christian Sprenger^1,6

¹Department of Systems Neuroscience, Medical Center Hamburg-Eppendorf, Hamburg, Germany, ²UCL Institute of Neurology, University College London, London, GA, United Kingdom, ³Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ⁴Department of Neuroradiology, Medical Center Hamburg-Eppendorf, Hamburg, Germany, ⁵Medical Radiation Physics, Lund University, Sweden, ⁶Department of Engineering, University of Cambridge, United Kingdom

Ex vivo histology remains the gold standard against which MRI biophysical models, e.g. the MR g-ratio which characterises the fraction of a fibre’s diameter that is myelinated, are evaluated. The MR g-ratio model requires a measure of myelin density, for which magnetization transfer saturation (MT) has been used as a biomarker. However, changes occurring post mortem, e.g. autolysis, temperature changes and fixation, significantly alter the MRI signal. Here we investigate how these changes impact MT. We found that MT decreased post mortem but greatly increased upon fixation. These effects are similar to reported changes of other established MRI myelin-markers.

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