Table 1.
Cellular Alterations Known to Follow TBI and Associated dMRI Changes
| Cell type or compartment | TBI‐related alterations | Tissue environment | Expected diffusion changes | Major citations | dMRI evidence |
|---|---|---|---|---|---|
| Neurons | cell loss necrosis and apoptosis | atrophy, cavitation, unmasking | decreased diffusivity and anisotropy, increased anisotropy | Sato et al., 2001; Chen et al., 2003; Coleman, 2005; Stoica & Faden, 2010 | Assaf et al., 1997; Van Putten et al., 2005; Immonen et al., 2009; Laitinen et al., 2015 |
| axonal injury | axon morphology changes including beading and varicosities | reduction in anisotropy and reduction in diffusion, especially in the axial direction | Johnson et al., 2013 | Mac Donald, Dikranian, Bayly, et al., 2007; Budde et al., 2009; Jiang et al., 2011; Li et al., 2011; Bennett et al., 2012; van de Looij et al., 2012 | |
| neural plasticity sprouting, arborization | increased number of coherent processes and new collaterals | increased anisotropy and/or changed orientation | Bach‐y‐Rita, 2003; Yiu & He, 2006; Werner & Stevens, 2015; Meaney & Smith, 2015 | Kharatishvili et al., 2007; Hutchinson et al., 2012; Sierra et al., 2015 | |
| Oligodendrocytes | demyelination direct damage, chronic pathology | degenerating or lost | decreased anisotropy | Armstrong et al., 2016 | Jiang et al., 2011; Budde et al., 2011; Li et al., 2014; Mac Donald, Dikranian, Song, et al., 2007 |
| myelination repair remyelination | regenerating | normalized anisotropy | |||
| Astrocytes | Hypertrophy | increased number or thickness of glial processes, possibly organized or directional | increased or decreased anisotropy, decreased diffusivity | Norton et al., 1992; Sofroniew, 2005, 2009; Sofroniew & Vinters, 2010; Wilhelmsson et al., 2006; Suzuki et al., 2012; Sun & Jakobs, 2012; Pekny et al., 2014; Burda et al., 2016 | Budde et al., 2011; Zhuo et al., 2012; Mac Donald, Dikranian, Song, et al., 2007 |
| proliferation | increased cellularity | decreased diffusivity | |||
| glial scaring | dense glia, increased organization | decreased diffusivity, increased anisotropy | |||
| Microglia | phagocytosis | amoeboid stage microglia | increased diffusivity | Kreutzberg, 1996; Graeber, 2010; Wake & Fields, 2011; Ziebell et al., 2012; Roth et al., 2014 | |
| neural repair and support | rod‐microglia | possible increased anisotropy | |||
| Intracellular space | cytotoxic edema | cell swelling | decreased diffusivity | Moseley et al., 1990; Pierpaoli et al., 1993; Bramlett & Dietrich, 2004 | Hanstock et al., 1994; Smith et al., 1995; Alsop et al., 1996; Unterberg et al., 1997; Assaf et al., 1997; Stroop et al., 1998; Albensi et al., 2000; Van Putten et al., 2005; Immonen et al., 2009; Frey et al., 2014 |
| Extracellular space | vasogenic edema | excess extracellular fluid | increased diffusivity |
Note: For each major cell type of the brain (column 1), different types of abnormalities that have been observed to follow experimental brain injury are categorized (column 2). The resulting changes to the tissue environment (column 3) and water diffusivity and anisotropy (column 4) are given as well as relevant citations for the neurobiological phenomenon (column 5) and dMRI observations (column 6).