Résumé
Purpose@#The corticospinal tract (CST) is a major tract for motor function. It can be impaired by stroke. Its degeneration is associated with stroke outcome. Diffusion tensor imaging (DTI) tractography plays an important role in assessing fiber bundle integrity. However, it is limited in detecting crossing fibers in the brain. The crossing fiber angular resolution of intra-voxel structure (CFARI) algorithm shows potential to resolve complex fibers in the brain. The objective of the present study was to improve delineation of CST pathways in monkey brains scanned by conventional DTI. @*Materials and Methods@#Healthy rhesus monkeys were scanned by diffusion MRI with 128 diffusion encoding directions to evaluate the CFARI algorithm. Four monkeys with ischemic occlusion were also scanned with DTI (b = 1000 s/mm2, 30 diffusion directions) at 6, 48, and 96 hours poststroke. CST fibers were reconstructed with DTI and CFARI-based tractography and evaluated. A two-way repeated multivariate analysis of covariance was used to determine significances of changes in DTI indices, tract number, and volumes of the CST between hemispheres or poststroke time points. @*Results@#CFARI algorithm revealed substantially more fibers originated from the ventral premotor cortex in healthy and stroke monkey brains than conventional DTI tractography. In addition, CFARI improved sensitivity in detecting CST abnormality compared to DTI tractography following stroke. @*Conclusion@#CFARI significantly improved delineation of the CST in the brain scanned by DTI with 30 gradient directions. It showed better sensitivity in detecting abnormity of the CST following stroke. Preliminary results suggest that CFARI could facilitate prediction of function outcomes after stroke.
Résumé
Purpose@#Investigation of stroke lesions mostly focuses on the grey matter (GM). White matter (WM) degeneration during acute stroke has remained understudied. In the present study, monkeys were employed to investigate the alterations in GM and WM in the brain following ischemic occlusion using diffusion tensor imaging (DTI). @*Materials and Methods@#Permanent middle cerebral artery occlusion was induced in rhesus monkeys (n = 6) using an interventional approach. Serial DTI was conducted on a clinical 3 T in the hyperacute phase (2–6 hours), 48, and 96 hours post-occlusion. Regions of interest in GM and WM of lesion areas were selected for data analysis. @*Results@#Mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) in WM decreased substantially during hyperacute stroke, similar to those seen in GM. No obvious fractional anisotropy changes were seen in WM during the hyperacute phase until 48 hours poststroke when significant fiber loss was observed. Pseudo-normalization of MD, AD, and RD was seen at 96 hours. Pathological changes in WM and GM were observed in ischemic areas at 8, 48, and 96 hours poststroke. Relative changes in MD, AD, and RD of WM were correlated negatively with infarction volumes at 6 hours poststroke. @*Conclusion@#The present study revealed the microstructural changes in GM and WM of monkey brains during acute stroke using DTI. The preliminary results suggest that AD and RD may be sensitive surrogate markers to assess specific microstructural changes in WM during the hyperacute stroke.