In vivo macrophage activity imaging in the central nervous system detectedby magnetic resonance

Cell-specific imaging has been proposed to increase the potential of magnet ic resonance imaging (MRI) for tissue analysis. The hypothezis of the prese nt work was that following intravenous injection of ultra-small particle ir on oxide, a contrast agent that accumulates in mononuclear phagocyte cells, macrophages with iron burden would be detectable by MRI within the central nervous system at sites of inflammatory cellular activity. In experimental autoimmune encephalomyelitis in Lewis rats (in which intense macrophage ac tivity results from both hematogenous macrophages and activated microglia), lesions have been seen by MRI as low signal intensities related to magneti c susceptibility effects induced by iron particles. Electron microscopy has revealed the presence of such particles within the cytoplasm of cells that had the morphological aspect of macrophages. Macrophage activity imaging m ight increase MRI capability with regard to the in vivo pathophysiological aspects of central nervous system (CNS) diseases and might help in therapeu tic trials in the numerous CNS diseases in which macrophages are involved. (C) 1999 Wiley-Liss, Inc.