Abstract
Cognitive impairment after traumatic brain injury remains hard to predict. This is partly because axonal injury, which is of fundamental importance, is difficult to measure clinically. Advances in MRI allow axonal injury to be detected after traumatic brain injury, but the most sensitive approach is unclear. Here, we compare the performance of diffusion tensor imaging, neurite orientation dispersion and density-imaging and volumetric measures of brain atrophy in the identification of white-matter abnormalities after traumatic brain injury. Thirty patients with moderate–severe traumatic brain injury in the chronic phase and 20 age-matched controls had T1-weighted and diffusion MRI. Neuropsychological tests of processing speed, executive functioning and memory were used to detect cognitive impairment. Extensive abnormalities in neurite density index and orientation dispersion index were observed, with distinct spatial patterns. Fractional anisotropy and mean diffusivity also indicated widespread abnormalities of white-matter structure. Neurite density index was significantly correlated with processing speed. Slower processing speed was also related to higher mean diffusivity in the corticospinal tracts. Lower white-matter volumes were seen after brain injury with greater effect sizes compared to diffusion metrics; however, volume was not sensitive to changes in cognitive performance. Volume was the most sensitive at detecting change between groups but was not specific for determining relationships with cognition. Abnormalities in fractional anisotropy and mean diffusivity were the most sensitive diffusion measures; however, neurite density index and orientation dispersion index may be more spatially specific. Lower neurite density index may be a useful metric for examining slower processing speed.
Highlights
Outcomes after traumatic brain injury (TBI) are often poor and remain hard to predict (Maas et al, 2017)
A comparison of moderate–severe lesion (n 1⁄4 20) and non-lesion TBI (n 1⁄4 10) patients showed no difference between the measures of reaction time (W 1⁄4 115, Punc. 1⁄4 0.33) and delayed memory recall (W 1⁄4 81, Punc 1⁄4 0.41) or executive function measured by DKEFS Stroop (W 1⁄4 123, Punc. 1⁄4 0.31)
No relationship was present for orientation dispersion index (ODI). These results suggest that Neurite Orientation Dispersion and Density Imaging (NODDI) can be used to clarify the location and extent of white matter (WM) damage, in such a way that it is relevant to improving our understanding of post-traumatic cognitive impairment
Summary
Outcomes after traumatic brain injury (TBI) are often poor and remain hard to predict (Maas et al, 2017). A major reason for this is the difficulty in determining the degree of underlying brain injury. Diffuse axonal injury (DAI) has a key role in the pathophysiology of TBI but it is difficult to measure clinically. Conventional diagnostic imaging approaches such as visual inspection of CT and standard MRI often underestimate the severity of DAI. Susceptibility weighted imaging is sensitive to diffuse vascular injuries, but diffusion imaging provides distinct information about the microstructure of the white matter (WM), which is disrupted by DAI and often appears normal on standard imaging (Kinnunen et al, 2011; Jolly et al, 2021). Major advances have been made over the last decade in the use of magnetic resonance imaging (MRI) to quantify post-traumatic axonal injury; the most sensitive approach is unclear
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