Investigating the influence of post-mortem interval on diffusion anisotropy of whole human brains

Motivation: The ISMRM-Diffusion-Study-Group recommends a post-mortem interval (PMI) under six hours to avoid degeneration in ex-vivo tissue for validation of microstructure parameters estimated using preclinical MRI. Fractional anisotropy (FA) deviation from the in-vivo value serves as a quality indicator.[1]Goal(s): Investigating the influence of PMI and tissue size on FA. Approach: Five human whole-brains (PMI 15-24h) and a temporal-lobe (TL) specimen (PMI 2h) were examined with diffusion MRI (dMRI) before and after fixation. Results: The FA of the unfixed whole-brain samples didn’t show differences to the in-vivo values, but between unfixed and fixed states. The FA of the TL specimen was unaffected during fixation. Impact: For the PMIs examined here, myelin decomposition may not significantly affect FA from dMRI of unfixed post-mortem specimens. However, it can affect whole-brain samples during immersion fixation - an effect that may be mitigated by using smaller samples.