In vivo MRA showed that the SNR-reducing effect of DM-was greater than that of D-USPIO (P , 0.05). With in vitro MRI scans, SNR was significantly lower in rabbits treated with dose 2 of DM-USPIO compared with D-USPIO treatment (P , 0.05), and it tended to be lower at dose 3 (P , 0.1). In conclusion, we suggest that DM-USPIO is superior to D-USPIO for the study of atherosclerotic lesions in rabbits.