Effect Of SPIO Particle Sizes On MR Imaging Properties And A Pilot Imaging Application Of The Ultra-small SPIO In Rat

Objective:?1?To investigate effect of particle size of SPIO nanoparticles on T1?T2 relaxation function.?2?The ultra-small particle size SPIO?Ultra-small SPIO,USPIO?was selected to explore its characteristics used as magnetic resonance T1-T2 double contrast agent in vivo in rats.Methods:SPIO nanoparticles were prepared by using co-precipitation chemical method with FeCl3·6H2O,FeCl2·4H2O,ammonia,dextran,citric acid,sodium hydroxide as the main raw materials.SPIO with 3 different particle sizes were obtained by adjusting the ratio of dextran and iron in the reactants.The X ray diffraction pattern,the particle size distribution and Zeta surface potential of SPIO were measured,and the T1 and T2relaxation efficiency at different magnetic field intensity?0.5,1.5 and 3.0 T?was studied in detail.Finally,clinical 3.0T MRI imager was used to study the contrast-enhanced imaging features of USPIO under different MRI sequences in rats.Results:SPIOs with 3 particle sizes?A:14.14±4.94nm,B:28.30±7.65nm and C:93.81±33.01nm?were successfully prepared,and the X-ray diffraction spectra were compared with the standard Fe₃O₄ powder diffraction data to determine those samples are Fe₃O₄.The relaxation properties of T1 and T2 of SPIOs at different magnetic field intensities were measured.SPIO with different particle sizes showed higher relaxation efficiency,and changed regularly with particle size.SPIO nanoparticles with small particle sizes have a lower r₂/r₁ ratio and are potential T1-T2double contrast enhancers.In addition,with the decrease of magnetic field,SPIO showed the trend of r₁ increasing and r₂ decreasing.Under low magnetic field,it had a lower r₂/r₁ ratio?sample A,0.5T=2.14,3.0T=9.25?,which was conducive to T1 sequence imaging.According to the results of rats in vivo imaging,USPIO on T2 weighted imaging sequence can significantly reduce the liver T2 imaging signal,at the same time,the T1weighted sequence?gradient echo sequence,short TE?,can significantly improve cardiovascular and liver T1 signal,and has longer imaging time window than small molecular contrast medium.Conclusion:Particle size is one of the important parameters affect SPIO relaxation efficiency.USPIO having lower r₂/r₁,are potential T1-T2double enhance contrast medium.It can be used as dual enhancement imaging of the viscera when the imaging equipment is available.In addition,SPIO has the advantages of biocompatibility and easy surface modification,and can be used for molecular imaging research later.