PREPARATION AND NEGATIVE MRI SPIN-SPIN RELAXATION ENHANCEMENT OF SUPERPARAMAGNETIC IRON OXIDES 
YU Kai-chao1,2, ZHANG Yan1, YANG Yun-huang2, LU Guang2, LIU Ma i-li1,2, YE Chao-hui1,2
Chinese Journal of Magnetic Resonance . 2002, (2): 143 -148 .