A longitudinal study of high-resolution diffusion tensor tractography in rats of middle cerebral artery occlusion

Abstract

Objective To evaluate the damage of white matter fiber tracts in the center and periphery of infarcts in the model rats of ischemic stroke.  Methods A total of 25 Sprague-Dawley (SD) rats were randomly divided into control group (N = 10) and middle cerebral artery occlusion (MCAO) group (N = 15). MCAO model was established by occluding with suture. At 3 h, 6 h, 1 d, 2 d, 3 d, 4 d and 7 d after model establishment, perform diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) at high-field 7.0T MRI, choose cortex, subcortex and corpus callosum of infarct side as regions of interest (ROIs) and calculate the values of fractional anisotropy (FA), mean diffusion coefficient (MD), radial diffusivity (λ║) and axial diffusivity (λ┴), choose internal capsule as ROI and calculate number of tracts (NT).  Results At different time points, FA value (P = 0.000, for all), MD value (P = 0.000, for all), λ║ value (P = 0.000, for all) and λ┴ value (P = 0.000, for all) in the cortex, subcortex and corpus callosum ofinfarct side had significant difference between 2 groups. As time extended, in MCAO group FA value in cortex, subcortex and corpus callosum of infarct side was slowly increased in superacute phase (≤ 6 h; P = 0.000, for all), obviously decreased in acute phase (6 h to 3 d; P= 0.000, for all) and kept stable in subacute phase (3 d to 8 weeks). MD value, λ║ value and λ┴ value were obviously increased in acute phase (P = 0.000, for all) and kept stable in subacute phase. FA value in cortex, subcortex and corpus callosum of infarct side (P = 0.003, 0.000, 0.000), MD value in subcortex (P = 0.013), λ║ (P = 0.012, 0.001) and λ┴ (P = 0.001, 0.036) values in subcortex and corpus callosum had significant differences between 2 groups. At different time points, NT value of infarct side had significant difference between 2 groups (P = 0.000). As time extended, NT value of infarct side in MCAO group was slowly decreased in superacute phase (P = 0.032), obviously decreased in acute phase (P = 0.000, for all) and kept stable in subacute phase. Compared to control group, NT value of infarct side in MCAO group was significantly lower at each time point (P = 0.000). DTT showed the white matter fiber tracts of infarct side in MCAO group were twisted and fractured. The damaged fibers tended to be around the edge of the lesion 1 d after MCAO model establishment.  Conclusions At the superacute phase to acute phase after ischemic stroke, nerve damage persisted until neural remodeling appeared in the subacute phase. DTT observed the damaged fibers tended to be around the edge of the lesion, suggesting the protective effect of damaged fibers surrounding the lesion.

DOI: 10.3969/j.issn.1672-6731.2018.01.008