RESUMO
Objective To observe signal changes induced by USPIO accords with iron swallowed by macrophages in brain tissue sections in rats. Methods Thirty-eight SD rats were divided into two groups randomly. Three of them were involved in sham operation group, other thirty-five rats were divided into five subgroups averagely according to 7.0T MR scanning time (6 h, 12 h, 24 h, 48 h and 72 h). After establishment of MCAO models, USPIO was injected to tail intravenous and monitored with high resolution MRI at different time point, while rats in control group were injected with the same dose of sodium chloride. Brain tissue wax section was acquired after MR scanning. Cell necrosis, iron particle and activated macrophages were observed with HE dying, Prussian Blue dying and CD68 immunochemistry staining respectively. Results The ischemic lesion was detected as hyperintense area on T2WI after occlusion and perfusion of MCA. The accumulation of USPIO appeared as hypointense on T2WI but hyperintense on T1WI. The maximum signal change was observed at 48-72 h in both T1WI and T2WI (P>0.05). The iron particle accumulation was found in the boundary of ischemic lesion and necrotic area with Prussian Blue dying. Activated microglia was manifested with CD68 immunochemistry staining, the number of microglia at 72 h was more than those of the other time points. Conclusion USPIO can be used as a contrast agent to monitor rat ischemic stroke in vivo, and the signal changes induced by USPIO approximately accord with iron swallowed by macrophages in brain tissue sections. The cells which swallow USPIO are mainly activated macrophages.