| Description |
Improved understanding of radiological signal changes and their relation to patient outcomes after ischemic motor stroke is needed to improve prognosis and recommend therapy. The corticospinal tract, in particular the region known as the posterior limb of the internal capsule (PLIC), is central to motor function, and this work proposes new, image-based methods for prognosis based on interhemispheric differences in the PLIC. Nine ischemic stroke patients received a baseline, 208 direction diffusion Magnetic Resonance Imaging (MRI) scan and clinical assessment 3-12 days post-stroke and were compared to 9 age-matched controls. Asymmetries based on the mean and Kullback-Leibler divergence in the ipsilesional and contralesional posterior limb of the internal capsule were calculated for diffusion tensor imaging (DTI) and diffusion spectrum imaging (DSI) measures from the baseline scan. Upper extremity Fugl-Meyer scores at 5-week follow-up from the stroke patients were then correlated with the asymmetry measures of the PLIC. The ipsilesional hemisphere PLIC differed significantly between stroke patients and controls in both DTI and DSI parameter maps. The orientation dispersion index best captured interhemispheric differences (mean and Kullback-Leibler divergence) in the PLIC and was highly correlated with upper extremity Fugl-Meyer outcomes (r2=0.89;p=0.0001). Generalized Fractional Anisotropy (GFA) also showed good correlation for mean difference (r2=0.67;p=0.0071) and KLD (r2=0.66;p=0.0079) in the PLIC. Stroke patients who displayed worse upper extremity functional outcomes at 5 weeks had elevated values of the orientation dispersion index in the ipsilesional PLIC, and decreased GFA relative to controls. These changes are likely indicative of demyelination of white matter. DSI measures such as the orientation dispersion index and GFA better capture these microstructural differences than DTI methods. The orientation dispersion index appears to be more sensitive to interhemispheric differences in the PLIC than GFA, and measuring the divergence of the ipsilesional and contralesional PLIC distributions through the Kullback-Leibler divergence is a promising method to relate asymmetries measured in MRI brain scans after stroke to functional outcomes. |
