Longitudinal assessment of MD and FA in four whole human brains using the DTI model

We investigated the longitudinal fixation effect of 4% paraformaldehyde and phosphate-buffered saline on diffusion imaging-derived mean diffusivity (MD) and fractional anisotropy (FA) across deep gray, cortical gray and white matter in human brains using suboptimal and optimal diffusion protocols with varying maximal b-values. We had two main findings: (1) a suboptimal diffusion protocol led to increased bias in the FA and MD up to 36.26% and 38.11%, the same trend was also observed for the across-brain variation; (2) MD changed by a maximum of 26.42% within the first 14 days in fixative and saturated afterward, whereas FA remained almost constant.