The NMR relaxivity of proton by dextran-magnetite (DM) complex was examined at temperatures from 20 to 80 degrees C. The decrease in T1 relaxivity with increasing temperature is due to the thermal activation of motion of water molecules in and/or surrounding DM particle. The decrease in magnetization of magnetite core is the secondary effect. The temperature dependence of T1 relaxivity was found to depend on molecular weight of dextran. The motion of dextran chains binding to core may affect the thermal activation of "heavy water" interacted with dextran. The Arrhenius plots of T1 relaxivity showed different slopes at 20-40 degrees C and 50-80 degrees C, while, no change in slope was observed for Fe(NO3)3, CuSO4 and Gd-DTPA solutions.
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