The Role of Dynamic Contrast-Enhanced MR in Evaluating Level III Collateral Circulation in a Rat Model of Acute Ischemic Stroke.

The study aimed to investigate the correlations between parameters of permeability magnetic resonance (MR) and the intensity of vasculature in the focal ischemic cortex of a rat model of middle cerebral artery occlusion. In the present study, sham operation or ischemic-reperfusion with tissue plasminogen activator (tPA) thrombolysis were performed in rats. Cranial MR scans and brain tissue samples were obtained from all animals. Brain slices were stained for immunohistological analyses with confocal fluorescence microscopy, and the intensities of microvessels and capillaries were calculated. Consistency between collateral circulation imaging classification and pathological vascular density was analyzed. We found that the K trans value and capillary intensity have the similar trends of declining and increasing, according to different time points, if compared with the sham operation group (P < 0.05). Permeability parameters have better correlations with capillary intensity, and K trans value had the best correlation at 4.5 h (kappa = 0.764, P < 0.001), while injection area under curve (IAUC) at 7 days (kappa = 0.725, P < 0.001). Susceptibility-weighted imaging (SWI) exhibited better correlation with microvessel intensity at both 3 days (kappa = 0.715, P < 0.001) and 7 days (kappa = 0.719, P < 0.001). In conclusion, the permeability parameters, such as IAUC and K trans map, can quantitatively assess capillary intensity, which may indicate angiogenesis categorized as level III collateral circulation after ischemic stroke.