A time-course study of actively stained mouse brains: DTI parameter and connectomic stability over one year

Abstract

While the application of diffusion tensor imaging (DTI), tractography, and connectomics to fixed ex-vivo tissue is a common practice today, there have been limited studies examining the effects of fixation on brain microstructure over extended periods. This time-course study reports the changes of regional brain volumes and diffusion scalar parameters, such as fractional anisotropy across twelve representative brain regions as measures of brain structural stability. The scalar DTI parameters and regional volumes were highly variable over the first two weeks after fixation. The same parameters were stable over a two to eight-week window after fixation which means confounds from tissue stability over that scanning window are minimal. Quantitative connectomes were analyzed over the same time period with extension out to one year. While there is some change in the scalar metrics at one year after fixation, these changes are sufficiently small, particularly in white matter to support reproducible connectomes over a period ranging from two weeks to one year post fixation. These findings delineate a stable scanning period during which brain volumes, diffusion scalar metrics and connectomes are remarkably stable.

Evaluation of early microstructural changes in the R6/1 mouse model of Huntington's disease by ultra-high field diffusion MR imaging

“…As an example, clinical studies have shown that formalin fixation promotes a decrease in MRI relaxometry (T1 and T2), a decrease in myelin water fraction (MWF) measurements but accounting for minimal changes in diffusion tensor imaging (DTI) parameters such FA and mean diffusivity, (MD) (Shatil et al, 2018). Specifically, to mouse brain DTI and tractography studies, there is some change in the scalar metrics at one year after fixation, these changes are sufficiently small, particularly in WM to support reproducible connectomes over a period ranging from two weeks to one-year post-fixation (Xiao et al, 2020).…”