Preparation And Study Of MRI Agent Based On Iron Oxide Nanoparticles

At present,magnetic resonance imaging(MRI)is a common method of medical detection and imaging,which has the safety of no radiation damage.However,it has been clinically found that the relaxation times of some different tissues or tumor tissues overlap each other,resulting in difficulty in diagnosis.Therefore,people began to study contrast agents for enhancing signal contrast and image resolution.The local relaxation characteristics of tissues can be changed by injecting contrast media to improve the contrast of imaging,so as to improve the accuracy of diagnosis.The contrast agent itself does not produce a signal,and by changing the relaxation efficiency of water protons in the local tissue in the body,it contrasts with the surrounding tissue to achieve the purpose of contrast.Contrast agents can be divided into T1 contrast agents and T2 contrast agents in principle.At present,the common contrast agents are gadolinium,manganese and iron series.In this paper,magnetic iron oxide nanoparticles used as T2 contrast agent were studied.Firstly,Fe3O4 nanoplates were synthesized by hydrothermal method,characterized by XRD,SEM and VSM.The effects of reaction temperature on the magnetic properties and morphology of Fe3O4 were studied.We found that the morphology and magnetic properties of Fe3O4 nanoparticles synthesized at 180 ℃ were the best.Next,we synthesized Ag@Fe3O4 composite nanoparticles by solvothermal method,which exhibited superparamagnetism at room temperature and had great application value.Afterwards,we studied the influence of doping transition metal ions such as Mn2+,Ni2+,Co2+ and Zn2+ on the magnetic properties of Fe3O4 nanoparticles,and analyzed the reason of this phenomenon in combination with theory.Finally,NiZn/CoZn ferrite composite magnetic nanoparticles with ferromagnetism were synthesized by combining soft phase NiZn ferrite with hard phase CoZn ferrite.However,Fe3O4 nanoparticles face problems such as agglomeration and oxidation.Appropriate surface modification can overcome these obstacles and improve physical and chemical properties.Different polymers such as polyethylene glycol(PEG),polyvinylpyrrolidone(PVP)and dextran(Dextran)modified Fe3O4 nanoparticles were synthesized by simple chemical co-precipitation method.The effects of PEG molecular weight,PEG addition,PVP addition and Dextran molecular weight on the morphology,crystallinity,size and magnetic properties of Fe3O4 nanoparticles were investigated.We found that the modified PEG2000 had the best modification effect,and when 3 mmol Fe3O4 nanoparticles were synthesized,the optimum addition amount of PEG or PVP was 0.5 g.We also found that the Dextran20000 modification effect is better than the Dextran40000.Finally,we characterized the relaxation rates r2 of PEG-PVP-Fe3O4 and Dextran-Fe3O4 are 201.72 mmol-1s-1 and 128.64 mmol-1s-1,respectively,which indicates that they have the potential to become T2 contrast agents.