We studied two kinds of iron oxide: DM-USPIO and D-USPIO (supplied by Meito Sangyo, Kiyosu, Aichi, Japan). Superparamagnetic iron oxide (SPIO) is a widely-used, safe, liver-specific contrast medium (Resovist ® ; Bayer Health Care Japan, Osaka, Japan); 27 carboxydextran covers the iron core of the iron oxide particles. The particle size of the D-USPIO used in this study is different from that of SPIO but its composition is similar. We prepared DM-USPIO by adding alkali-treated mannan to D-USPIO ( Figure 1) were the same for D-and DM-USPIO (28 nm, 15 mg/mL, 0.028 erg ⋅ gauss -2 ⋅ g -1 , respectively).