Central nervous system inflammatory response after cerebral infarction as detected by magnetic resonance imaging

Brain inflammation contributes to the tissue injury caused by ischemic stroke. Macrophages as the most abundant inflammatory cell population in stroke lesions can be visualized using ultrasmall superparamagnetic iron oxide (USPIO) as a cell-specific contrast agent for magnetic resonance imaging (MRI). The aim of our present study was to delineate the inflammatory response during experimental cerebral infarction by means of USPIO-enhanced MRI and to correlate the spatial distribution of USPIO-induced MR signal alterations with cellular infiltration and iron deposition. To this end USPIOs were administered to Wistar rats 5 days after photothrombotic cerebral infarction. MR imaging at 7 T performed 24 h later displayed a rim-like signal loss around the infarction in the USPIO treated animals. On histological brain sections obtained from the same animals after MRI the distribution of iron and ED1+ phagocytes was in full spatial agreement with the signal loss seen on T2*-weighted images. Our study validates USPIO-enhanced MRI as an important tool for the noninvasive visualization of brain inflammation in stroke and other CNS pathologies.