[Usefulness of magnetite as an MRI contrasting agent in an experimental cerebral ischemic model evaluation of injecting time point].

The superacute stage of focal ischemia can be visualized using T2-weighted MRI following the injection of superparamagnetic iron oxide particles (magnetite). In this study we evaluated the optimal time point, i.e. the time producing the strongest signal, for the injection of magnetite using T2-weighted MRI following left parmanent middle cerebral artery occlusion (lt.-PMCAO). Male Sprague-Dawley rats were anesthetized and the left middle cerebral artery (lt.-MCA) was permanently occluded. Magnetite was then injected into the femoral vein after 20 to 30 min of lt.-PMCAO. T2-weighted MR images were taken immediately, and 15 and 30 min after magnetite injection. A high signal area at the region of the lt.-MCA was clearly seen on the T2-weighted MRI immediately after magnetite injection. However, it became less clear after 15 min, and by 30 min could not be distinguished. These results suggest that magnetite should be injected immediately prior to T2-weighted MR imaging during the superacute stage of focal ischemia.