Investigating microbleeding in cerebral ischemia rats using susceptibility-weighted imaging

Purpose: To detect the distribution and prevalence of cerebral microbleeding (CMB) in rats after acute ischemic stroke using susceptibility-weighted imaging (SWI).

Method: After middle cerebral artery occlusion, 3T MR scanning was performed on 10 rats at 4h and 24h after ischemia. T2-weighted images (T2WI), T2 maps and diffusion-weighted images (DWI) were generated to estimate the severity of the brain ischemia. The SWI data were used to analyze location counts, size and distribution of the CMBs. The brain injury was evaluated and determined by hematoxylin and eosin (H&E) staining.

Result: At 24h after onset of ischemia, 13 CMBs were found in seven of the nine ischemic rats, whereas only two CMBs were found at 4h after ischemia onset in one of the nine ischemic rats. All visible CMBs detected in the SWI data were located in the ischemic lateral cortex, with diameters ranging from 0.2 to 0.5mm. In addition, we observed thickened vessels near the CMBs in the ischemic hemisphere in the SWI minimum intensity projections that did not appear in the symmetrical regions on the contralateral hemisphere. Histopathological results confirmed the CMBs, and increased microvascular density was observed in the ipsilateral hemisphere.

Conclusion: SWI technique allows the detection of CMBs and the accompanying thickened vessels in vivo in a rat model of cerebral ischemia, which appear to be challenging tasks using T2WI and DTI. The results reported in this work provide a better understanding of the pathophysiological mechanism of acute stroke.