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Figure 5 Striking Positive Signal Enhancement Corresponding to Macrophage-Rich Plaque on IRON Images

On conventional magnetic resonance (MR) images, subtle areas of signal hypointensity (negative contrast) were detected in the aorta (solid arrows and overlaid regions of interest in panels B and D) of hyperlipidemic rabbits after MION-47 injection compared with baseline images (A and C). On IRON images, tissue was homogeneously suppressed at baseline (E and G), while positive signal was seen after MION-47 injection (solid arrows in panels F and H). The positive signal corresponds to iron deposition in matched slices on histology (fast nuclear red staining in panels I and K and combined acid phosphatase and Prussian blue staining in panels J and L). The dotted red lines on the MR images correspond to the cross section of the vessel. In both Watanabe and control rabbits, positive signals were present in paraspinal ribs (dotted arrows in panels F, M, and O) and in lymph nodes (arrowheads in panel O). As expected, normal rabbits showed no plaque on histology (N and P). Abbreviations as in Figure 4.