A MRI Study On Structural Changes Of Gray And White Matter In Chronic Strokes

Objective:To investigate the neural mechanisms of motor impairment after stroke, we explored the structural changes of gray and white matter, and the relationship between them by combining voxel-based morphometry (VBM) analysis and diffusion tensor imaging (DTI) in chronic basal ganglia stroke patients.Methods:Twenty well-recovered patients with a unilateral chronic infarction of basal ganglia area were compared with twenty-two age-and sex-matched healthy participants. GE3.0T HDX MR Scanner with an8-channel head coil was used to obtain high resolutions anatomy images and DTI data. The comparison of gray matter volume (GMV) between the two groups was performed by VBM8software in the whole brain level. We defined the areas where were significantly different in GMV as masks and obtained their GMV values. The preprocessing of DTI data was carried out by the FSL4.1software. Bilateral pyramidal tracts (PT) between the precentral gyrus and pontine were reconstructed. And the DTI parameters (fiber number [Num], fractional anisotropy [FA], mean diffusivity [MD], axial diffusivity [λ‖], radial diffusivity [λ⊥]) of PT were calculated. We tested the side differences in the diffusion indices of the PT in the two groups using a paired-samples t test. Asymmetry indices of fiber number and other parameters comparing ipsilesional with contralesional hemispheres were used to assess the structural integrity of the PT and correlate with GMV values obtained by VBM. For the phased analysis, we divided the PT into8segments per centimeter and compared their diffusion indices between the two groups. All of the datas were analysed with the SPSS software package version18.0(SPSS Inc., Chicago, IL, USA).Results:1. Decreased GMV in ipsilesional primary motor cortex (M1) was detected in patients group by VBM (P<0.05, FDR correction).2. In the DTI study, we did not find any significant changes in the diffusion indices of the contralesional PT in the stroke patients. However, Num and FA value asymmetry significantly differed between the two groups with lower values in the patients’ipsilesional hemispheres, while MD and λ⊥value asymmetry increased in patients group (P<0.05).3. Phased analysis revealed that the segments (Seg) of the ipsilesional PT exhibited differences in diffusion indices, such as the rFA decreased in Seg3-7, and the rMD increased in Seg3-6. We also found that the impairment of the ipsilesional PT was centered on the primary lesion, and extended both above and below the lesion in our study.4. In addition, the changes of GMV values in ipsilesional Ml obtained by VBM were correlated with the rFA and rλ⊥of the ipsilesional PT in the patients group.Conclusions:1. Chronic infarction of basal ganglia area induced structural changes in ipsilesional Ml which may infered structral injury in cortical area remote from lesion site.2. Secondary degeneration of the ipsilesional PT was centered on the primary lesion, and extended both anterograde and retrograde in chronic basal ganglia stroke patients. In addition, closer to the primary lesion, the degeneration was more seriously.3. Retrograde degeneration of the ipsilesional PT which manifested as axonal degeneration and demyelination appears to account for the atrophy of ipsilesional Ml.4. Structural changes in ipsilesional M1were correlated with the integrity of the ipsilesional PT in chronic strokes. And the GMV of ipsilesional Ml decreased with the secondary degeneration of PT.