In rabbits treated with dose 3 of D-or DM-USPIO (n = 3, respectively), MRA images obtained in vivo showed irregularities, seen as spotty signal voids in the aortic wall. These were interpreted as indicating iron deposits. Before treatment with either agent, the aortic wall appeared smooth, without any evidence of atherosclerotic plaque formation. The SNR of the aortic wall was significantly lower after treatment with D-and DM-USPIO than before treatment. The difference between the SNR obtained before and after the injection of nanoparticles was significantly greater in rabbits treated with DM-rather than D-USPIO (P , 0.05) (Figure 2 ).