Introduction: Diffusion tensor imaging (DTI) is increasingly being used to interrogate microstructural changes in white matter integrity during developmental and pathological processes. We have applied DTI to the widely used middle cerebral artery occlusion (MCAO) model of cerebral ischemia.
Methods: We performed ex vivo DTI 35 days after 60 min transient focal ischemia in male spontaneously hypertensive rats and generated fractional anisotropy, mean, axial and radial diffusivity maps. Regions of interest corresponding to external capsule, corpus callosum and internal capsule were compared among sham and stroked rats. We also compared tractographic projections of white matter fiber patterns and examined white matter integrity by Luxol fast blue histological analysis. We also determined infarct lesion volumes at 24 hr post-ischemia by T2-weighted magnetic resonance imaging or at 35 days by histological staining with cresyl violet.
Results: We found evidence of alterations in external capsule and internal capsule, but not corpus callosum, as represented by decreased fractional anisotropy. We also observed increased mean, axial and radial diffusivities in the external and internal capsule regions of interest. The size of the ischemic lesion detected subacutely by T2-weighted magnetic resonance imaging or at 35 days by histological staining correlated with the extent of decline in fractional anisotropy in the affected structures. Tractography revealed disruption of fiber trajectories through the external capsule and reorientation of fibers within the caudate putamen of rats subjected to MCAO. Similarly, loss of white matter integrity in the external capsule and increased white matter density in the caudate putamen along the infarct border zone was also evidenced by Luxol fast blue staining.
Conclusions: Diffusion tensor imaging therefore allows for monitoring of white matter injury and reorganization in hypertensive rats.
Patient Care: Better understanding of ischemic cerebral injury will provide valuable information for cerebrovascular diseases.
Learning Objectives: Diffusion tensor imaging detects succesfully white matter injury and reorganization in hypertensive rats.