Preparation And Application Of T₁-T₂ Dual Modal MRI Contrast Agent Based On Magnetic Nanoparticles

Magnetic resonance imaging(MRI)has shown great advantages in the early diagnosis and treatment of tissue necrosis,tumors and other diseases.In order to solve the problem of tumor localization more accurately,MRI contrast agents were introduced.Magnetic nanomaterials have been widely used as MRI contrast agents due to their good biosafety,excellent magnetic properties and readiness of surface modifiability.The limited sensitivity and accuracy of current single-modal MRI contrast agents,which limited the application of magnetic nanoparticles in MRI.To improve the sensitivity and spatiotemporal resolution of MRI,a potential strategy is to develop dual-modal MRI contrast agents.The relaxation rate of the contrast agent is an important parameter to measure the imaging effect of the contrast agent.Therefore,the magnetic properties of magnetic nanomaterials can be improved by changing the factors affecting the relaxation rate,such as element doping,size distribution,and morphology.Improving the longitudinal(r₁)and transverse(r₂)relaxation rates,and then developing a T₁-T₂ dual-mode imaging contrast agent with excellent performance is the main content of this thesis.In this thesis,three kinds of magnetic nanomaterials were synthesized:Mn Fe₂O₄,Fe Pt@Fe₃O₄,Fe Pd@Mn O.The effects that element doping,size distribution,and morphology on r₁ and r₂ were studied.The dual-mode imaging potential of three magnetic nanomaterials was investigated and the application of Fe Pt@Fe3O4 in glioma imaging was explored.This thesis mainly includes the following parts:First,Mn Fe₂O₄ was synthesized by organic high-temperature pyrolysis method.The effect of Mn²⁺doping on the relaxation rate was analyzed.The introduction of Mn²⁺strengthened the interaction between Mn Fe₂O₄ and water protons and improved r₁to a certain extent.The high saturation magnetization endowed Mn Fe₂O₄ with a high r₂.After injection of Mn Fe₂O₄,it was observed that the T₁ image of the subcutaneous tumor area of the mouse was brightened and the T₂ image was obviously darkened.It is verified that the Mn Fe₂O₄ synthesized by this method has good MRI effect.Second,Fe Pt@Fe₃O₄ core-shell nanomaterials with different sizes were synthesized by one-pot method.The effects of different core-shell size on r₁ and r₂ in Fe Pt@Fe₃O₄ were studied.The saturation magnetization of Fe Pt@Fe₃O₄ is controlled by the interface coupling effect,and then r₁ and r₂ are controlled.The T₁-T₂ dual-mode imaging contrast agent Fe Pt@Fe₃O₄ with good performance was obtained by adjusting the core and shell sizes.After injection of Fe Pt@Fe₃O₄,the T₁ image became obviously brighter and the T₂ image became obviously darker in the area of subcutaneous tumor and glioma.It proves that the Fe Pt@Fe₃O₄ can be used as a kind of good T₁-T₂ dual-modal MRI contrast agent.Third,flower-like Fe Pd@Mn O was synthesized by one-pot method.The relaxation properties of Fe Pd@Mn O as MRI contrast agent were analyzed.The unique flower-like structure endowed Fe Pd@Mn O with large surface area which enhanced water proton exchange efficiency with Mn²⁺,and made Fe Pd@Mn O excellent T₁imaging.The exchange coupling effect caused by the ferromagnetic-antiferromagnetic structure of Fe Pd@Mn O is the main reason for the transverse relaxation.It is show that Fe Pd@Mn O has the potential as an MRI contrast agent.The synthesis method involved in this thesis is simple.The synthesized three MRI contrast agents:Mn Fe₂O₄,Fe Pt@Fe₃O₄,Fe Pd@Mn O,have good magnetic imaging effect and biosafety,and have broad application prospects in tumor localization,medical research and other fields.In this thesis,by exploring the influencing factors of the relaxation rate of the contrast agent,the magnetic properties of the magnetic nanomaterials were regulated,and the relaxation rate of the contrast agent was enhanced to different degrees,and the MRI effect of the contrast agent was improved.It has important research significance for the preparation of T₁-T₂ dual-modal imaging contrast agents with better performance in the future.